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Quaternary geomorphic surfaces on the northern Perris Block, Riverside County, California: Interrelationship of soils, vegetation, climate and tectonics

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Quaternary geomorphic surfaces on the northern Perris Block, Riverside County, California: Interrelationship of soils, vegetation, climate and tectonics

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Content QUATERNARY GEOMORPHIC SURFACES ON THE NORTHERN PERRIS BLOCK, RIVERSIDE COUNTY, CALIFORNIA: INTERRELATIONSHIP OF SOILS, VEGETATION, CLIMATE AND TECTONICS by BARBARA ELIZABETH HANER A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (Geological,Sciences) April 1982 UMI Number: DP28560 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI DP28560 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 U N IV E R S IT Y O F S O U T H E R N C A L IF O R N IA T H E G R A D U A TE S C H O O L U N IV E R S IT Y PA RK LOS A N G E LE S . C A L IF O R N IA 9 0 0 0 7 This dissertation, written by ......BARBARA, ELIZABETH..MNER....... under the direction of h.QX... Dissertation C om mittee, and approved by a ll its members, has been presented to and accepted by Th e Graduate School, in partial fulfillm en t of requirements of the degree of D O C T O R O F P H I L O S O P H Y / Dean D a te... DISSERTATION COMMITTEE Chairman 7 _r. ^ I gX q a - ' pocket" ACKNOWLEDGMENTS I wish to express my sincere thanks to Dr. Donn Gors- line, chairman of my dissertation committee, for his con tinued interest, assistance and many suggestions during all phases of this study. Members of my dissertation committee, Dr. Floyd Sabins, Dr. Robert G. Douglas, Dr. Bernard Pipkin and Dr. James Pomerening are also thanked for their gui dance and support. Dr. James Pomerening, California State Polytechnic University, Pomona generously gave of his time for advice on soils in both the field and laboratory. His discussions on soil morphology were most helpful in estab lishing the Quarternary soil chronosequence for the area studied. I also appreciate being able to use the soil laboratories at Cal Poly during the summer of 1981. The pedogenic carbonate horizons were dated by Dr. T.L. Ku and his research group at the University of South ern California who were willing to experiment with clay soil sequences from a mesic environment. Results from this data provide an important base to establish the geomorphic history of the area. The patience and help of Mr. Dick Tilforth and Mrs. Bonnie Busenberg of Rancho Santa Ana Botanic Garden, Clare mont in identifying plant specimens was much appreciated. Discussions with members of the San Bernardino Flood Control District and the Santa Ana River Water Board __________________________________________________________________ii Authority have enabled me to obtain data to document recent changes of the Santa Ana River. Dr. James French, U.S. Geological Survey, Mr. Hal Weber, California Division of Mines and Geology, and Dr. John Foster, Rasmussen and Associates were all willing to supply helpful discussion of the recent structural development of the Transverse Ranges in southern California. To my husband Dr. David A. Haner, I wish to express my deep appreciation for his constant support whether digging holes in the field, holding tapes, and especially during the final stages of thesis completion. 111 TABLE OF CONTENTS Page ACKNOWLEDGMENTS................................... ii LIST OF FIGURES. ............................... vii LIST OF TABLES.......................... viii ABSTRACT............................................ ix I. INTRODUCTION....................................... 1 General Statement................................. 1 Objectives of Study........ 4 Area of Investigation............................. 5 Previous Investigation........................... 11 II. COLLECTION AND ANALYSIS OF DATA................. 14 Field Techniques.................................. 14 Laboratory Techniques............. 19 Statistical Methods.................. 20 Nomenclature....................................... 20 III. GEOLOGIC SETTING.................................. 22 General Statement................................ 22 San Bernardino Mountains.............. 23 San Gabriel Mountains..'................. 25 Perris Block....................................... 27 San Timoteo Badlands............ 30 San Andreas Fault................................. 31 San Jacinto Fault................................. 33 Chino-Elsinore Fault Zone........................ 34 IV. CHARACTERISTICS OF MEDITERRANEAN REGIONS....... 37 Climate..................... 37 Temperature............. 37 Wind Patterns................................... 38 Rainfall......................................... 41 Hydrology........................... 44 Origin of the Native Vegetation.......... 55 Holocene Plant Communities....................... 56 Coastal Sage Scrub.............. 57 Valley Grassland................................ 5 9 Foothill Woodland........... 60 Riparian Woodland............................... 61 Vegetation, Fire and Flood....... 62 ________________________iv Page V. GEOMORPHIC AND SEDIMENTARY FACTORS.............. 65 Granite Weathering................................ 65 Bedrock Weathering............................. 6 6 Physical Weathering............................. 67 Biological Weathering.......................... 6 9 Soil Formation on Upland Areasw . ................ 6 9 Fallbrook Series................................ 71 Vista Series........................... 72 Cieneba Series.................................. 75 Granite Sediment........................... ...... 76 Drainage Basin Morphometry....................... 86 Morphometric Parameters........................ 88 Drainage Density. . ............................. 92 Bifurcation Ratio............................... 102 Mean Stream Lengths........................... . 105 Floodplain Morphology............ ................ 110 Channel Form.................................... 110 Bars ................................. ..... 115 Sand Flats................... ............... ..... 119 Sedimentary Characteristics..................... 120 Floodplain Sediments........................... 121 Environmental Factors............................ 127 Vegetation Patterns............................... 130 Active Floodplain and Sand Flats.............. 131 Terrace T10..................................... 133 Terrace T9....................................... 135 Tributary Streams............................... 136 Discussion........................................ 136 Eolian Deposits................................... 140 Morphologic Features.......... ................... 142 Longitudinal Dunes................... .......... 142 Sand Plain....................................... 143 Blowout Depressions and Parabolic Dunes...... 143 Coppice Dunes............................. . 144 Dune Soils............................... ...... 145 Dune Field History............................. 148 Alluvial Fan Deposits............................. 149 Erosion Surfaces................................. 151 Box Springs Canyon Surface (Tl)............... 153 Jurupa Surface (T2)............................ 154 Canal Surface (T3).............................. 156 Limonite Surface (T4).......................... 158 Riverside Grand Terrace (T5) ................. 162 Pedley Terrace Surface (T6)................... 165 Lytle Creek Surface (T7)....................... 166 Mira Loma Surface (T8)......................... 167 Soil Development on Erosion Surfaces........... 16 8 v Page Recent Soils and Associated Sediment......... 16 9 Relict Soils..................................... 175 Fossil Soils...................... 176 Van Buren Road....... 177 60th Street Terrace...... . 180 Hamner Bridge Soil Profile.................. 180 Age Dating and Discussion........................ 187 VI. TECTONIC ACTIVITY................................. 193 Introduction......................... 193 Internal Faulting (Mockingbird Canyon Fault)........................ 193 Boundary Faulting (San Jacinto and Elsinore Faults).................... 195 VII. SUMMARY AND CONCLUSIONS.......................... 200 REFERENCES ..................................... 215 APPENDIX I. Stratigraphy, Climate, Vegeta tion................ 228 APPENDIX II. Drainage Morphology............... 24 0 APPENDIX III. Soil Descriptions................ 248 vi LIST OF FIGURES Figure Page 1. Regional geology of southern California.......... 6 2. Quadrange index map................................. 9 3. Area and fault location map (backpocket) 4. Santa Ana River Flood and precipitation records ........................................ 47 5. Comparison of yearly discharge patterns before extensive flood control (circa 1900) and the present 4 9 6. Location of sediment samples and drainage basins...................... 77 7. Comparison of textural parameters for granite grus and Mockingbird Canyon. . . 7 9 8. Comparison of textural parameters for granite grus and Pigeon Pass............................... 81 9. Sediment sorting and population distribution of Santa Ana River and tributaries.................. 84 10. Pigeon Pass drainage network...................... 93 11. Sycamore Canyon drainage network.............. .. 95 12. Mockingbird Canyondrainage network.......... 97 13. Graphic presentation of bifurcation ratio........ 103 14. Graphic presentation of mean stream length...... 107 15. Diagram of floodplain channels and correlation with ripple form.................................... 112 16. Diagramatic sketch of bar and floodplain mor- . phology............................................. 116 17. Analysis of sediment samples from the San Gabriel Mountains......................... 122 18. Santa Ana River depositional environments.. 125 19. Terrace Surface location map (backpocket) 20. Vertical description of Wisconsin dune succes sion and underlying Riverside Surface........... 146 21. Soil and topographic relationships, Surfaces T1-T6................................................ 173 22. Cross-section of fossil soils exposed at Van Buren and Jurupa Road junction, Pedley. ...... 178 23. Vertical profile of fossil soils, Hamner Bridge. 182 vii LIST OF TABLES Table Page 1. Terrace Chronosequence. . .......................... 152 2. Comparison of Soils................................. 190 3. Correlation of Geomorphic, Climatic and Tec tonic Events in the Riverside-Corona Area....... 201 Appendix I - Stratigraphy, Climate, Vegetation 4. West Coast Stratigraphic Chart................... 229 5. Glacial Chronology........ .................... . .. 230 6. Location of Meterologic Stations................. 231 7. Comparison of Temperature, Precipitation for Riverside, San Bernardino, Corona............... 232 8. Comparison of Regional Mean Temperature . 233 9. Comparison of Regional Mean Precipitation...... 234 10. Comparison of Longterm Climatic Regional Averages of Precipitation and Temperature...... 235 11. Comparison of Discharge Regimes pre-1900 and Present Day........................... 236 12. Vegetation.......................................... 237 13. Granite Weathering Table............ 239 Appendix II - Drainage Morphology 14. Main Drainage...................................... 241 15. Comparison of All North-Facing Drainage Basins........... 242 16. Comparison of All South-Facing Drainage Basins.............................................. 243 17. Comparison With Other Southern California Watersheds.............................. 244 18. Pigeon Pass......................................... 245 19. Sycamore/Tequesqui to............................... 246 20. Mockingbird........................................ 247 Appendix III - Soil Pedon Descriptions ABSTRACT Ten geomorphic surfaces reflecting periods of tectonic uplift, structural stability and climate change near River side and Corona, southern California are preserved as 1) bedrock and alluvial strath terraces; 2) alluvial fans and 3) fill terraces. These surfaces descend to the Santa Ana floodplain from the Pleistocene Paloma Surface (a relict river and alluvial fan system 240 m. above present river level). Mid Pleistocene uplift caused fan fragmentation, rapid downcutting, and formation of two bedrock strath sur faces. Paleosols indicate periodic sedimentation interrupted major soil forming periods on the Riverside Grand Surface formed during the Illinoian glacial and arid Sangamon interglacial stages. The youngest paleosol caliche hori zon is 97,000 ±5,000 years B.P. (234U dating). Regional westward tilting caused channel incision and abandonment of this surface. Wisconsin climatic cooling initiated major watershed erosional cycles and accompanying removal of deeply wea thered hi11slope debris. Aggradation on the lowered flood- plain ceased when vegetation growth responded to more humid conditions, but further erosion occurred late in the plu vial cycle. During the ensuing interglacial, sediment on aggrading floodplains was redistributed into one dunefield. ix Later dune form modifications resulted from surface aban donment and reduced sediment supply. Extreme aridity during the Xerothermic (8,000-5,000 years B.P.) caused floodplain aggradation. Gurrent erosion of the Santa Ana River floodplain, including the 1862 flood, is correlated with watershed deforestation, changing agricultural practices, and urbanization. Increased flood control and lowered water tables have caused floodplain de gradation and vegetation changes. Mediterranean summer drought intensifies water loss and the broad marginal sand flats adjacent to the braided Santa Ana River channel are reworked into shifting sand sheets. Syntectonic erosion and climatic perturbations alter nating with periods of stability have preserved a stepped topography which contrasts with the highly dissected fron tal margin of the Transverse Range. Bound by active trans form faults which have caused tectonic compression and up lift in southern California, the Perris Block has responded as a stable granitic buttress zone accomodating recent orogenic activity by tilting and minor uplift. x 1 CHAPTER 1 INTRODUCTION GENERAL STATEMENT Geomorphic analysis of processes and changes which have operated within a defined geographic area requires a systematic approach integrating three basic morphometric techniques. First, the landforms must be mapped, measured and their spatial distribution and form analyzed. Under standing the processes which are currently fashioning these land surfaces at the present time constitutes the second stage. Finally an analysis of sedimentary deposits and evaluation of processes and chronologic sequence of events occurring in the past completes the study which must integrate all known variables. Present-day processes are not necessarily the pro cesses which have created the landforms preserved today. Palimpsest reconstruction of past events in southern Calif ornia must also consider the role of tectonics and synde- positional modification of sediment and landforms. Major climatic changes have occurred in the last 11,000 years influencing sediment supply, vegetational changes and de nudation of valley slopes. Contemporary base level changes and tectonic tilting can also cause superimposition of drainage patterns and steepening of valley gradients adjacent to uplift. 2 Distinct slope gradient changes on homogeneous bedrock represent multicyclic periods of landscape development. Fluvial terraces represent levels of former valley floor and the correlation of height, and internal composition contribute to the geologic and climatic evolution of an area. This periodicity may involve tectonic, climatic and drainage pattern changes. During periods of landscape stability soils develop on these surfaces later to be buried, eroded or left as residuals during periods of in- stability. A soil profile is a result of dynamic processes which combine at different rates to produce diagnostic features characterized by rapid, slow and irreversible processes. Buried and relict paleosols can be used to interpret age, development-time and processes involved in erosional land surfaces. Drainage basin morphology reflects the interaction be tween independent changes such as climate, bedrock type and tectonic uplift; and dependent variables of the adja cent source region such as relief, aspect, topography, vegetation and susceptibility of surface material to ero sion. Streams adjust towards longitudinal equilibrium pro files as hydrologic variables interact so that stream power is sufficient to transport the sediment load. De gradation occurs when runoff and stream power is in excess 3 of that needed to transport sediment load and aggradation reflects insufficient stream power to transport the load. This may reflect climatic, vegetational and weathering changes within the regional watershed. Equilibrium periods are characterized by the formation of floodplains, stream terraces and lateral erosion into the adjacent hill slopes. Tectonic disruptions may involve uplift and lateral dis location adjacent to faults and also regional preferential tilting. The effects of tilting may be more evident along streams parallel to this trend than those oriented perpen dicular to this direction. Stream power may increase as a result of climate and corresponding plant community changes. These reflect changing temperature, precipitation and rainfall intensity. Vegetation changes may also increase soil erodibility as groundcover density provides protection to hillslopes. This can result in alluviation or degradation of streams as material is removed from the hillslopes depending upon the load that a stream is carrying. The initiation of change following a period of landscape stability can pro duce accelerated downcutting and preservation of surfaces as fill terraces. Man's impact on the environment must also be consid ered as can occur by deforestation on hillslopes, farming methods, urbanization and increased surface runoff as streets are developed and areas of natural soil seepage are removed. OBJECTIVES OF STUDY The study was initiated to establish the age and spa tial distribution of the geomorphic surfaces preserved in the Riverside-Corona area. Interrelationships of climate, vegetation, parent material, time and tectonics were eval uated as processes which have fashioned the surfaces in the past. Their continuing role as agents promoting de gradation or aggradation at the present time was also con sidered as well as recent changes in agriculture and ur banization. This area is of interest because the margins of the Perris Block are bound by two major transform faults, the San Jacinto and Lake Elsinore faults. Strike-slip motion within these fault zones is contained within narrow zones of overlapping enechelon faults which may create pull-apart basins or high standing positive regions. In contrast the Perris Block is composed of relatively homogeneous, mas sive coarse igneous granite, tonolite and granodiorite and has remained a stable area responding to regional pressures by slow uplift and minor westward tilting. This contrasts with the rapid vertical tectonics, deformation and ero sional history of the adjacent central Transverse Range. The Riverside-Corona region is on the northern margin of the Perris Block and provides an area to study responses to tectonic events along the margin of a stable block. Soil development, terrace profiles and migration of the Santa Ana River could be utilized to develop a geomorphic history of the study area since the Pasadenan Orogeny. AREA OF INVESTIGATION The Perris Block was first defined by English (1926) as the massif between the San Jacinto and Elsinore-Chino fault zones, bounded to the north by the "San Gabriel" (Cucamonga) fault. English did not define the southern and eastern boundaries, but subsequent work by Woodford et al. (1971) used an approximate boundary determined by a complex group of faults southeast of Murrieta (Fig. 1). The block is part of the northernmost extension of the crystalline igneous and metamor-phic rocks of Cretaceous and earlier ages which form the predominantly northwest trending Peninsular Range Geomorphic Province of southern California. Most of the block is a moderately high area between 1,100' (336 m) and 2,500' (762 m) on which six erosion surfaces, four of them almost level surfaces, have developed during the Plio-Pleistocene (Woodford et al. , 1971). This study examines the most northern area of the block which forms an abrupt northward facing escarpment and descends to the Riverside Grand Terrace. This terrace FIGURE 1. Regional geology of southern California. Base map and fault patterns largely after Rogers, 1965. Letters represent the following cities: C, Corona; LA, Los Angeles; NB, Newport Beach; R, Riverside; SA, Santa. Ana; SB, San Bernardino. f : • V . * ; SAN v G /i B R IJE L; j:* ;•; j ; ; • ' ^ G ^ : ‘ ; VA^iO^v'.-'A'-: V ‘ S o ^ V - * * . ^ • * ■ : ^i : - ; - . ' . ^ / ;•;.#;• ~y; . : • ; s a n . b e r n a r d i no. • • . v . : ; . • . : : • ; • . • ; . ; ••^.•T^K ' »*.'/:^~t ' •'• • • . • . ' ' . ' • MOUNTAIN3 -. ■ • :’:- O f ‘‘v ‘ T W * 8 . * * - • * . - • • . • • w."; /;\\Yw:iV*vV::: : : > . * J r - - V r - : . • • • ' \ fault \ \ \ ^ SAN FERNANDO V A L L E Y \ \ \ ’* X^S B UPPER SANTA ANA n • ^ * g*briEl ^ALLEy V A L L E Y • - \ 7> r^y - • • • «Vv • . • : • . - : . * ♦> ALLUVIUM OF RECENT v / OS. A s 1 0 I mile* AND PLEISTOCENE SEDIMENTARY ROCKS OF TERTIARY AND CRETACEOUS CRYSTALLINE AND METAMORPHIC ROCKS - KNOWN FAULT IN F E R R E D F A U L T C ONCEALEO FA U L T 8 is part of the Santa Ana Basin. Today the Santa Ana River is entrenched in a shallow, east-west trending granite bed rock gorge as it crosses this area. Locally this gorge is known as the Riverside Narrows, a term which effectively describes the sudden change of the broad floodplain of the Santa Ana River to a confined zone within the gorge. The research area is located approximately 6 0 miles (96 km) east of Los Angeles in western Riverside and San Bernardino Counties, California, between latitudes 33 de grees and 51 minutes and 34 degrees and 03 minutes north and longitudes 117 degrees and 15 minutes and 117 degrees and 30 minutes west. Sections of the U.S. Geological Sur vey 15 minute topographic series covering the study area are indicated on Figure 2. The area covers approximately 180 square miles (468 sq km). The northern boundary is marked by the isolated granitic hills forming Stover Mountain and the Jurupa Hills. The Jurupa Hills rise to over 1800 feet (558 m) and on their northern flank rise abruptly from recent alluvial fan material derived from the San Gabriel Mountains. These hills are the most nor therly extension of the Southern California Batholith and have a complex magmatic and contact metamorphic history. Their present isolation may represent the original topo logy of the batholith as it intruded into the surrounding country rock. vey ,9 FIGURE 2. Index map indicating U.S. Geological Sur- 7.5 Minute Series Quadrangles used in study. 10 QUADRANGLES SAN BERNARDINO SOUTH FO NT AN A GUASTI CORONA NORTH RIVERSIDE WEST RIVERSIDE E A S T S T E E L E PEAK LAKE M ATHEW S CORONA S O U TH S A N T A ANA RIVER LOS ANGELES RESEARCH AREA PACIFIC OCEAN NASA OVERFLY SAN DIEGO 11 The western margin of the study area is marked by Arlington Mountain and the La Sierra Hills. Arlington Mountain is over 1880 feet (583 m) high and is part of the Perris Block. The La Sierra Hills are separated from Arlington Mountain by the narrow Arlington Gap (Fig. 1). The southern boundary consists of the arcuate River side escarpment which descends steeply from the planar topographic expression of the Perris surface on the nor thern margin of the Perris Block. This granitic escarpment ranges in height from 1400 (434 m) to 1600 feet (488 m). except along the steep fault bounded Box Springs Mountains which rise to 2400 feet (732 m). The maximum east-west dimension of the area is 16 miles (26 km) and north-south dimensions vary between 10 miles (16 km) near Riverside and 14 miles (23 km) near Corona. Much of the area is urbanized. Riverside, the largest city, has a population of over 16 9,000, and has undergone a 21.1% population increase since the 1970 census. Popu lation within the Inland Empire Conurbation Region composed of Riverside-San Bernardino-Ontario has also tripled since 1970 at the expense of land previously used for dairying, citrus orchards, vineyards, and truck farming (U.S. News and World Report, 1981, a and b). PREVIOUS INVESTIGATION Geologic interest in this region was first initiated 12 by two, factors still important today, water and transporta tion. Although emphasis on the potential rail routes de scribed by Blake (1856) and the irrigation problems men tioned by Schuyler (1896-1897) have changed, these early reports provide data on the superficial deposits in the San Bernardino-Riverside area before intensive farming and urbanization. The hydrology, water storage capacity, and subsurface topography of the Santa Ana River and associated valley basins have been described in publications of the U.S. Geological Survey Water Supply Bulletins and the California Water Resources Control Board (Mendenhall, 1905; Eckis, 1934; Troxell et al., 1951; Dutcher and Garret, 1963; and French, 1972). Recent technical data is published by the Santa Ana Watermaster to monitor changes in river drainage flow while a law case on water usage is pending between Orange County and San Bernardino County (1976, 1979, 1981). Eckis (1934) also defined the Riverside Grand Terrace and previously had described alluvial fans in the Cucamonga area where he suggested that movement on the San Jacinto fault had preserved part of the Rialto Bench (1928). Re cent geomorphic studies of Quarternary deposits have been made of the San Bernardino Valley (Clarke, 1978, 1980) and the Santa Ana Canyon west of Corona (White, 1976). Seismic activity and well defined topographic expres 13 sion of recent fault movement along the San Jacinto and Chino/Elsinore fault zones have been well documented (Sharp, 1967, 1972, 1975? Weber, 1976). The acceptance of the plate tectonic hypothesis for the evolution of western North America (Atwater, 1970) has resulted in a renewed interest in deformation, uplift, structural style and stability at the junction of two major geomorphic provinces in southern California; the east-west trending Transverse Ranges and the northwest trending Peninsular Ranges. This junction has resulted in offset along the San Andreas fault (Crowell, 1962; Woodburne, 1975) and complex fault patterns and strain relationships in the Transverse Ranges (Dibblee, 1975; Baird et al. 1974). Rapid aseismic activity is re flected throughout southern California by uplift, basin development and rapid infill (Foster, 1980; Rodgers, 1979; Yeats, 1978 and 1981) . Continued suburban growth in this critical region continues to generate the need for detailed geologic monitoring and research in this area. 1.4 CHAPTER 2 COLLECTION AND ANALYSIS OF DATA FIELD TECHNIQUES The study area was surveyed using standard 1:24,000 United States Geological Survey topographic sheets (Fig. 2). Quaternary surficial deposits and associated landforms were delineated and erosion surfaces on granitic bedrock were also marked (Fig. 3, backpocket). The position of the Riverside Escarpment was denoted as that place where surface gradient increased from 5% to 15% and usually co incided with increased stream gradient, knick points, change in valley morphology, or drainage capture. Between interfluves the edge of this escarpment may also be de signated by residual watershed remnants and tors. Granitic weathering forms were observed and indications of the effects of recent fires were noted. Field checking and correlation utilized soil maps of western Riverside and San Bernardino Counties (Soil Survey Staff, 1971, 1981). These soil maps are the basis of all soil interpretation in this study. Color, overlapping 9 by 18 inch (23 by 46 cm) photo graphic sheets taken during NASA Mission 239 in 1973 at a scale of 1:33,000 were used in the central portion of the field area between latitude 33° 55' and latitude 34°.04' 15 and longitude 117° 22* 30" and longitude 117° 30* (Fig. 2). This particular flight path yielded excellent coverage of the Riverside Escarpment and was used to extend fault lines and lineaments. These were later field checked. Stream and valley drainage network reflects topograph ic, lithologic, pedologic, and vegetational controls. Drainage density is defined as the "length of all streams per unit drainage area" (Horton, 1932). The portion of the first order streams can be estimated by: 1. Strict interpretation of the drainage network with blue lines on topographic maps (not appli cable in areas of intermittant drainage). 2. Contour crenulation 3. Air photo interpretation 4. Field inspection Some areas were field checked but usually this proved to be of limited success due to access problems without using four-wheel drive vehicles. Bauer. (1980), estab lished that first order streams could be recognized by the contour crenulation method accurately in southern California by using the criteria that: a. Contour crenulations must not form an angle of more than 120 degrees. b. At least two consecutive contour crenulations must be deflected into the general slope in order to substantiate a certain depth of incision into the valley slope. Three canyons, Mockingbird, Pigeon Pass, and Sycamore/ 16 Temesquito, were examined and compared using drainage mor phology, sedimentology, and soils. Mockingbird Canyon was always chosen as a comparison to the two later drain age basins because it presently does not drain into the Santa Ana River but terminates on the Riverside Grand Ter race Surface. Several types of stream terraces are found within the study area, and the terminology used to describe these fea tures is that of Leopold and Miller (1957). A fill terrace is formed by valley aggradation and subsequent channel in cision into the fill terrace deposits. These are left as remnants of higher levels of valley aggradation but pre servation of these deposits may not always be in the form of classical paired terrace because of shifting stream drainage channels and erosion. If this aggradation is associated with a long period of landscape stability soil profiles can develop and these can be used to establish relative ages of the terraces and the affects of both climatic and tectonic events which may have been major factors in their development. Information regarding the location, magnitude and frequency of these events may also be inferred from this information. Periods of accelerated downcutting into these fill deposits may also be tentatively correlated with periods of climatic change. Downcutting implies an increase in in stream power which can be achieved either by increased rainfall or a decrease in sediment load (Bull, 1979). Vegetational changes reflecting temperature and rainfall variables or land use modifications, also affect the inter action. Temperature and rainfall periodicity and intensity, interact with other variables in the drainage basin sub system. Climatic changes affect vegetation associations and distributions which may increase the potential for soil erosion, and input of sediment into the drainage basin. This change is particularly important at the Pleis- tocene-Holocene climatic change and also the Xerothermic Period associated with an intensification of arid condi tions which occurred 8,000 years ago (Van Devender, 1977). Strath Terraces are formed by the erosional widening of the valley floor into bedrock and are preserved by a change in base level as a result of increased stream down- cutting. Alluvial material may be deposited on strath surfaces but there may be a considerable period of time between their formation and this depositional event. Strath terraces may also be confused with exposure of hori zontal joint patterns on slopes underlain by granite which locally form bedrock surfaces and act as a local .base level control. The exposure of these surfaces may also reflect removal of a more extensive alluvial fill and local terrain controls such as slope aspect, microclimates, and vegeta- 18 tion. The ages of some surfaces have been assigned by the occurrence of paleosols and their relative position in vertical river cliff and gully sides. Erosion surface age has also been interpreted from their relative position in a sequence of descending erosional levels. The lower the surface and the closer to present base levels, the younger it is in a formational chronosequence. This statement must be modified as the present base level is higher than the lowest in the area as backfilling and depositional fill has occurred since the Wisconsin maximum sea level lowering. Continual regional tectonics have also modified baselevel considerations. Relative age may also be assigned util izing degree of soil development, pebble weathering rates found in some terrace exposures, and sediment accumulation rates. This is called a chronosequence. Soil horizons were delineated and sampled according to standard United States Department of Agriculture, Soil Conservation Service procedures (Soil Survey Staff, 1951). Horizon nomenclature, consistency, color, structure, cu- tans, effervescence and pH were determined in the field. A collection of fluvial samples was also made from three transects along the Santa Ana River and from streams draining into the river. These were compared with samples of weathered granite grus which was also analyzed as it 19 represents the source rock for deriving sediment in the area. LABORATORY TECHNIQUES All sand fractions were analyzed using the settling tube coarse fraction analysis procedure at the University of Southern California. This data was processed through a programable calculator,to obtain textural moment measure parameters. Soil samples were air dried and crushed to pass through a 2 mm sieve. Any material retained on this sieve was weighed, calculated, and reported as percent gravel. The m a t e r i a l p a s s i n g th r o u g h t h e s i e v e w as r e t a i n e d f o r f u r t h e r p a r t i c l e - s i z e d e t e r m i n a t i o n u s i n g s t a n d a r d s o i l t e c h n i q u e s . Pedogenic carbonate material was prepared as outlined in Ku et al. (1979) and analyzed to determine the poten tial age of the carbonatic horizons. These carbonates are associated with clayey and loamy soils and may be con taminated by other soil forming factors, i.e., air borne dust. Therefore unlike desert soil caliche layers or petrocalcic horizons, this can only be regarded as a rela tive dating tool, but one which is still useful in an area where no wood fragments have been .preserved. Carbonate dates are probably too young for the soil horizons because 20 weathering probably has occurred since their formation. STATISTICAL METHODS A computer program was developed for linear fits of drainage morphology data. Drainage basin data were cast in logarithmic numbers to obtain a least squares linear fit with respect to stream order as defined by Horton (1945). From this analysis, bifurcation ratio and stream length ratios were determined. Standard deviations were calculated for the two parameter mathematical model based on the variance of the linear fit using propagation errors as described by Young (1963) . The least square fit lines are plotted with field data and one standard deviation con fidence limits are indicated for comparison of data scat ter. NOMENCLATURE European Neogene Epochs, North American mammalian stages, and west coast (Californian) marine stages as re cognized by Berggren and Van Couvering (1974) are used for stratigraphic terminology (Appendix I, Table 4). Re cent glacial stratigraphic time scales from the Sierra Nevada are used for relative dating of Quaternary events (Appendix I, Table 5). Weathering parameters, soil properties, and Potassium- Argon (K-Ar) dating have been used to delineate two major post-Sherwin Pleistocene glaciations, the Tahoe and Tioga (Burke and Birkeland, 1979). This two-fold division was first established by Blackwelder (1931) but Sharp (1972), later subdivided the Wisconsin into Tioga-Tenaya-Tahoe-Mono Basin/Casa Diablo glacial deposits. Relative dating tech niques and problems associated with local glacial changes involving aspect, catchment area and relief when corre lating from valley to valley can distinguish first order glaciations but not minor fluctuations at the stadial level (Porter, 1971). This has resulted in the return to the simpler classification for the Wisconsin in California. Holocene events have been inferred from a variety of sources including sea level changes, archeology, shifting aboriginal tribes and primary changes in their food pro curement, and botanical evidence for a major period of intense aridity, the Xerothermic, between 8,000 and 5,000 years ago (Davis, 1978; Van Devender, 1977). 22 CHAPTER 3 GEOLOGIC SETTING GENERAL STATEMENT The physiographic history of the upper Santa Ana River and of the surrounding area is closely related to its structural history. The landforms and Quaternary geo- morphology are chiefly adjustments to changes in elevation related to mountain building which occurred in middle Pleistocene time and modified by deposition and erosion in late Pleistocene and Holocene. Within and adjacent to this area are five major structural rigid blocks which form the boundaries of the Upper Santa Ana Valley (Fig. 1). These blocks are bounded by major faults on which recurring movement has occurred since at least the Pliocene. This culminated in the mid-Pleistocene Pasadenan Orogeny. Ero sion from these blocks has significantly influenced the depositional history of the entire region causing major shifts in drainage pattern and contrasting Quaternary landforms. The northern boundary is formed by the San Gabriel and San Bernardino Mountains, which together comprise the eastern and central portions of the Transverse Range struc tural and geomorphic province (Fig. 1). These mountains are separated by the San Andreas fault which also forms 23 the southern boundary of the San Bernardino Mountains. In tense uplift by as much as 5,000 feet (1550 m) occurred during the Pasadenan Orogeny which has supplied large amounts of detritus to infill the structural depression be tween this area and the southern boundary of the region. In contrast, only one block on the southern boundary, the Santa Ana Mountains, has undergone active uplift and tilting. Immediately adjacent to the Transverse Ranges, the depressed margins of the San Jacinto and Perris Block have been buried 1400 feet (434 m) and 1200 feet (372 m) respectively by recent alluvium along a hinge line flexure extending east from the Jurupa Mountains to Redlands (Dutcher and Garrett, 1963). SAN BERNARDINO MOUNTAINS This mountain range, bounded by the northwest-trending faults adjacent to the Mojave Desert and the San Andreas fault on the south, rises abruptly on the northeast side of the San Bernardino Valley. At least 5,000 feet (1550 m) of uplift occurred during the Pasadenan Orogeny. The straight south-west front is the dissected scarp of the San Andreas fault. From Cajon Summit to the Santa Ana Gorge the mountain crest rises gradually from 5,000 feet (1550 m) to 7,500 feet (2325 m). East of this the skyline is dominated by several high peaks, the highest, Mt. San 24- Gorgonio 11,502 feet (3566 m) , was scoured by alpine gla ciers during the late Wisconsin (Sharp et al., 1959). Complex sets of lateral strike slip, normal, and thrust faults separate the area from the Mojave Desert to the north and the Salton Trough . to the south. Internal faulting along the two main branches of the San Andreas fault, the north branch being the Mill Creek-Mission Creek fault, and the south branch, the Banning fault through San Gorgonio Pass, results in juxtaposition of two distinctive rock suites. The north block is composed of gneiss and metasedimentary roof pendants of Paleozoic quarzite and marble, folded possibly during the Permian, and intruded by quartz monozonite of the Mojave granite batholith. The southern area is a gneiss plutonic complex with mylonites and Pelona Schist, although the latter is only found in the isolated, low hills of the San Bernardino Valley (Dibblee, 1975) . The northern block was reduced to an area of low re lief by late Cenozoic time. Near Barton Flats, in the cen tral San Bernardino Mountains, "a series of terrestial sands and gravels" (Vaughn, 1922), is overlain by basalts dated at 6.2 my by Woodburne (1975). These beds have been correlated by Dibblee (1975) and Foster (1980) with the Crowder Formation in the Cajon Valley. These beds have been dated as Blancan/Hemphilian (Foster, 1980). A syn- 25 orogenic alluvial fan/fluvial sequence reflects the first renewal of tectonic uplift within the San Gabriels. This sequence could have drained either west into the Pacific, where the shoreline was along the approximate line of the Puente Hills (Fig. 1) or east into a proto Salton Trough which had begun to form as the Gulf of California devel oped, 5 to 6 million years ago (Larsen, 1972). This tec tonic movement in the late Pliocene, culminated in wide spread uplift and thrust faulting in the Pleistocene. In tensive erosion created the many deep canyons with exten sive alluvial fans. Continued uplift into the Recent has left many of these fans with abandoned, deeply weathered fan head surfaces adjacent to the frontal scarp. Two par ticularly large fans have been deposited in Cajon Pass and at the mouth of the Santa Ana Gorge near Mentone. SAN GABRIEL MOUNTAINS The San Gabriels, forming the central Transverse Range, are separated from the San Bernardino Mountains at Cajon Summit by the San Andreas fault. This fault forms the northern boundary of this region with the Mojave Desert, and the southern boundary is formed by the Cuca monga fault. The east-west trending Cucamonga fault is part of the frontal fault system of the Transverse Range and connects with the Sierra Madre, Raymond Hill, and 26 Santa Monica fault which all mark the southern boundary of this province. The range is higher and more rugged west of the San Jacinto fault zone (Fig. 3). Within the complex en echelon zone between the San Andreas and the San Jacinto faults, the San Gabriels are depressed and average 3,700 feet (1147 m) lower than the height of the main range to the west. The igneous metamorphic basement complex is composed of folded gneiss, schists and metasediments ranging in age from Pre-Cambrian (1.7-1.45 billion years) to Mesozoic (65 M years). They are intruded by diorites ranging from Permo-Triassic age (Mount Lowe Granodiorite) to Cretaceous and Miocene (Morton, 1975). The distinctive Pelona Schist, a green schist facies rock, is exposed on the northern and eastern margin of the mountains and beneath the Vincent Thrust. Continental fluvial and alluvial fan sandstones and conglomerates outcrop on the northern flank of the moun tains. Recent detailed work by John Foster (1980) , shows that recent synorogenic history reflects that of the San Bernardinos, but sections indicate that approximately 14 miles (22.5 km) of right lateral offset has occurred on the San Andreas since the Plio-Pleistocene and the area has undergone major vertical tectonics during this period. It was initiated by broad upwarping of a late Cretaceous- 27 early Tertiary eroded surface into the "San Gabriel Arch." Late Miocene, Pliocene and Pleistocene deposits have all been tilted and deformed. The present drainage into the San Bernardino Valley along Cajon Creek may be relatively recent (100,000 years, Foster, pers. comm.). Uplift of the San Gabriels also shed an enormous volume of sediment into the Santa Ana Valley and caused the southward migration of the Santa Ana River to its present course (French, 1972). Along the flanks of the mountains are prominent old, deeply weathered alluvial fan head conglomerates (Eckis, 1928). PERRIS BLOCK- This province is bound on the east by the San Jacinto fault, on the west by the Chino/Elsinore faults and on the north by the Cucamonga fault (English, 1926) (Figure 1). The most northerly positive topographic expression of this region are the Jurupa Hills. This range is composed of Mesozoic plutonic rocks intruded into metasediments of Triassic age (MacKevett, 1951). These metamorphoric sedi ments and roof pendants of gneiss, marble, quartzite and schist are found throughout the range. The sequence of igneous intrusion in increasingly younger age is 1) Mount Wilson Granodiorite, 2) Bonsall Tonalite, and 3) San Marcos Gabbro. Ur-Pb dates on zircons from Crestmore and Mount 28 Rubidoux have yielded dates of 109 My and 120 My which are consistent with other dates from the northwestern margin of the Peninsular Range Granite batholith near Corona (Armstrong and Suppe, 1973; Everndern and Kistler, 1970). The maximum elevation of the Jurupa Hills is 2,225 feet (685 m) with an average concordant summit range of 1600-1700 feet (496-527 m) . Crestmore and Slover Mountain are isolated inselbergs of the Jurupa Hills. Existence of roof pendants, flow structures at contact margins, and isolation from the main mass of the Peninsular Range sug gest that some of the topography in the Jurupas may repre sent the original topography as the granite intruded and cooled against the country rock. The structural trend of the Jurupas is N70W, but al though . the northward facing frontal slope is steep, ex ceeding 35 degrees, the many embayments do not suggest a frontal fault process parallel to the Cucamonga fault. The depth of fill between the Jurupas and the San Gabriels ex ceeds 4,000 feet (1230 m) (Dutcher and Garrett, 1963). Sands from the Cucamonga and Lytle Creek Fans spread around the hills, but do not cover an old alluvial plain extending from the south side of the Jurupas to the Santa Ana River. Large climbing dunes ascend the north side of the Jurupas, but this material was derived from extensive Wisconsin dune fields to the east. 29 South of the Santa Ana River, the La Sierra Hills are also composed of Bonsall Tonalite and granodiorite. They contain no contact metamorphic rocks. They are separated from the main Perris Block by the Arlington Gap. This nar row gap is approximately a mile wide (1.61 km) but does not appear to be structurally controlled and in the past has been a water gap for the Santa Ana River. The prominent Perris Block escarpment is composed of granodiorite except for an area of metasediments between McAlister Road and Mockingbird Canyon. K-Ar dates show that the axial portion of the range was implaced between 95-115 My ago and becomes younger towards the east. This also follows a trend of uplift on the west and deepest erosion on the east. Topographically, the northern part of the Perris Block is a gently south and east sloping series of erosion sur faces except in the Lake Mathews area, which slopes west. There are four erosion surfaces preserved beneath which are found buried channels (Woodford et al., 1971). The oldest channels infilled by Lake Mathews' sediments contain mam malian fauna of Lower Pliocene (Clarendonian) age. These buried channels are bevelled by the Perris surface which is overlain by the Santa Rosa basaltic sequence (Mann, 1955). The base of this sequence has been dated as 8.310.5 My old by K-Ar dating (Hawkins, 1970). Drainage was towards the 30 east arid concentrated into ancestral San Jacinto and Mur rieta River systems. This was followed by major valley deepening (3 My ago) and then a period of backfilling to create the Magee and Gavillan-Lakeview surfaces (Woodford et al., 1971). The Paloma Surfaces (the youngest) formed during the mid-Pleistocene and is presently 800 feet (244 m) above the Santa Ana River floodplain. Morton (pers. comm.) has found clasts of Palona Schist derived from the San Gabriel Mountains in alluvial fan sediment on the Paloma Surface. SAN TIMOTEO BADLANDS East of the San Jacinto Fault and adjacent to the San Bernardino Valley, Lower Pliocene Mount Eden lacustrine sediments are uncomformably overlain by fluvial sands, gravels and silts of the San Timoteo beds and form clas sical badland topography. These gray, yellow or brown gravel, sand and silt beds are derived from weathered granitic rocks. Fossils of Irvingtonian age have been found in these beds (English, 1953). This formation is found east of the San Jacinto fault except for one location at the mouth of Reche Canyon and one small locality adjacent to the Cucamonga Fault where intensely folded, gray gravelly sand forms a narrow es carpment and ridge. English (1953) demonstrated that the 31 Reche Canyon locality could be matched with a locality 12 miles (19 km) to the south. Fanglomerates are also dis placed from their source area by a similar amount. The Reche Canyon locality demonstrates that the San Jacinto fault has been extremely active in the late Pleistocene and the 10 miles (16 km) of lateral displacement proposed by Bartholomew (1972) for the San Jacinto fault in the Imperial Valley could also have taken place along its northern trace at approximately the same time and rate. The San Timoteo beds were warped into a broad anticline with an east-west axial trend. SAN ANDREAS FAULT The right-lateral motion, potential hazards and dis placement on the San Andreas fault has probably been the subject of more papers and controversy than any other geo logic feature in California. Locally, the fault forms the scarp boundary of the San Bernardino Mountains. The San Andreas has been likened to a conveyor belt shuffling an assemblage of Pacific lithospheric plates northwards with reference to the North American plate. Estimates of movement within the late Tertiary, Plio- Pleistocene, range from 50 miles (80 km) (Barrows, 1979) to 10 miles (20 km) (Foster, 1980). The east-west trend of the Transverse Ranges across the 'normal' northwest 32 orientation of the San Andreas structural trend has been interpreted as the cause for rapid subsidence and formation of small elongate basins during the late Tertiary in both the offshore Continental Borderland and the Los Angeles, Ventura and the Ridge Basin areas. These subsidence rates have been estimated to be in the range of 1300-1500 m/My to accomodate the fill of these basins which ranges from Miocene to Pliocene (Yeats, 1978, 1980). River exploitation of the fault zone has produced two contrasting forms. Cajon Creek, exploiting the mylonite crushed zone between the Pelona Schist and the San Bernar dino block within the fault zone, has created a broad linear valley ranging between 0.5 (0.8 km) and 3 miles , (5 km) wide. River capture by Cajon Creek has also col lected drainage basins which previously drained east into the Mojave River. This capture took place approximately 60,000 years ago (Foster, 1980). This stream is out of proportion to the valley it occupies and is a classic mis fit stream. Prior to the major Pasadenan uplift, the Santa Ana River may have drained southwest into a proto-San Bernar dino Valley or into the San Timoteo trough. A major tri butary of the Santa Ana River exploits the Mill Creek or north branch of the San Andreas but the Santa Ana River maintained its southwest course creating an impressive 33 superimposed deep gorge as it crosses both branches of the San Andreas. The river is offset right laterally approxi mately two miles (3.6 km) between these two faults. SAN JACINTO FAULT ' „ The San Jacinto fault zone is comprised of a series of en echelon fault strands which form a straight and con tinuous zone of right lateral slip in southern California from the Anza-Borrego Desert to the Devil’s Punchbowl near Wrightwood (Sharp, 1967, 1975). These overlapping fault strands are about 6 to 14 miles (10-23 km) long. Strain is taken up along either of these branches and may be taken up more on one than the other. Sharp (1975) proposes that the area between the bounding faults can be warped up to create blocks or down to form linear basins such as the San Jacinto Valley. In the San Bernardino Valley the paired faults are the Glen Helen and Claremont faults and in the San Jacinto Valley, the Claremont and Casa Loma fault. Aligned and linear gullies, deflected stream courses, faceted ridges and slump scars indicate that the active break of the Claremont fault is immediately to the east of Reche Canyon. The upper end of Reche Canyon has been also an area of fault activity as indicated by the intensely dissected alluvial fan in Reche Canyon. Beneath the alluvial fill of the San Bernardino Valley the faults 34 act as ground water barriers, the most important being the Bunker Hill Dyke (Dutcher and Garrett, 1963). This dyke causes groundwater lost by percolation in the loose gravels and alluvial fill of the upper San Bernardino Valley to rise so that there is always perennial flow of water on the Santa Ana River between Riverside and Prado Dam. Sharp (1967), proposed cumulative right lateral move ment along the San Jacinto fault of approximately 15 miles (24 km) since the Pliocene, although other workers (Eng lish, 1953; Bartholomew, 1979) have proposed displacement of 11 miles (18 km) and 18 miles (2 9 km) of post-Pliocene movement for different segments of the fault zone. Fre quent earthquakes of magnitude four and greater attest to the continued activity of this fault zone (Elders et al., 1973). CHINO-ELSINORE FAULT ZONE This fault zone, along with the Whittier fault bounds three major structural blocks, a) the Santa Ana Mountains bounded by the Elsinore and Whittier faults, b) the Puente- Chino Hills block bounded on the southwest by the Elsinore- Whittier faults and by the Chino fault on the northeast, and c) the Corona-Chino Valley block on the northeast side of the Chino fault (Figure 1 and 3, backpocket). Vertical movement on the Elsinore fault and associated 35 minor en-echelon faults has created a deep, narrow fault graben. The principal faults dip steeply southwestward. Geomorphically youthful features along the San Jacinto fault suggest activity in the Holocene (Weber, 1976). In itiation of the predominently vertical movement probably began in late Pliocene and early Pleistocene (Gray, 1961). Uplift of 2500 to 300 feet (770 to 922 m) has been sug gested (Weber, 1976) to account for wind gaps and ancestral drainage of the San Jacinto River. Right lateral motion of 6 to 6.5 miles (9-11 km) has also been proposed by Weber (1976). Uplift is most impressive on the southwest side and the alluvial debris from the Santa Ana Mountains has created a large fan at Corona. Growth of this fan has forced Temescal Wash to entrench on the northeast side of the Trough. Entrenchment has removed fault evidence, but the stream may be excavating crushed fault zone rock. The Chino fault branches away from the Elsinore fault south of Corona and extends north along the eastern margin of the Puente Hills. Holocene movement has occurred (Gray, 1961). No fault trace can be seen crossing the Santa Ana River, but analysis and comparison of the 1902 .Corona Quad rangle with the present day, suggest gradient decrease along the proposed trace of the fault (Weber, 1976). An unnamed fault was mapped by Gaede (1969) and re cognized in subsurface topographic analysis by French . . 36 (1972), as bounding the eastern edge of the area continuing north from Temescal Wash (Figure 3). Linear gullies and uplift of old alluvium suggests Wisconsin and Holocene movement on this minor branch fault. The junction of the Whittier-Elsinore-Chino Faults form a giant .wedge that tapers southeastward. Evidence for right lateral movement on the Whittier fault and re verse thrust motion on the Chino Fault causes both verti cal movement on the northeast side and eastward lateral movement on the north side. Such movement may have caused rotation and complex folding in the down warped block and was postulated by Gaede (1969) as accounting for sub- .. surface structures in the small Prado-Corona oil field. Recent work on the river terraces on the north bank of the Horseshoe Bend in Santa Ana Canyon, west of this triple junction, indicates 400 feet (123 m) of uplift has occurred between 22,000 years B.P. and 68,000 B.P. (White, 1980). 37 CHAPTER .4 CHARACTERISTICS OF MEDITERRANEAN REGIONS CLIMATE The area's climate is typical of all Mediterranean- type climatic regimes. Long, hot, dry summers with mean monthly temperatures in the mid-seventies (°F) are fol lowed by mild wet winters. More than 70 percent of the annual precipitation falls in the rainy season of November through April. Rainfall is variable with less than 5 inches (12.7 cm) during dry years and as much as 25 inches (6 3.5 cm) in wet years. Vegetation growth is largely limited to the spring when temperatures rise and the soil moisture content is high. Prolonged droughts can dras tically reduce vegetation density. T em p e r a tu r e The Riverside area is within the subtropics being at a latitude of 34 degrees north. A comparison of three stations, Corona, Riverside and San Bernardino, and five regional stations (Appendix I, Tables 6, 7, 8) indicate mean annual temperature range from 61.5 to 63.4°F reflect-, ing increasing distance from ocean cooling breezes and more interior locations. The coldest month, January, has an average temperature of 51.5°F while the average tempera ture of the warmest month, August, is 75°F. The previous 38 month, July, has an average of 74.9°F indicating the in tense build-up of temperature in this Inland Valley where summer daytime temperatures frequently reach 105°F. Even comparing temperatures for 1975, a drought year, and for 1980, a wet year (Table 8) indicate that there is little yearly difference in temperature. Wind Patterns Mountains surround the inland San Bernardino/Riverside area. The valley floor elevation ranges from 570 to 900 feet (177 to 279 m) in the Riverside/Corona area. In con trast, the San Gabriels and San Bernardino Mountains rise to over 10,000 feet (3048 m) and 11,000 feet (3353 m). The average height of the Perris Block is 2,000 feet (610 m). Cajon Summit is 4,000 feet (1219 m) and provides a low pass into the Mojave Desert. The Banning-Beaumont Gap at ap proximately 2,600 feet (806 m) provides airflow to the Sal- ton Trough. Through the Puente Hills, whose average elevation is 1,300 feet (400 m) three wind gaps exist. The lower, more southerly gap is Santa Ana Canyon and connects with the Orange County coastal plain. The other outlets are in the north at the end of the Puente Hills. The Pomona-Walnut Valley, a former valley occupied by the ancestral Santa Ana River is several hundred feet lower than the foothill gap 3 9 over low, rolling hills near San Dimas. These gaps con nect with the Los Angeles Basin (Figure 1). The two moun tain passes allow desert air to flow into the region under certain conditions. The wind gaps in the Puente Hills provide access for cool coastal breezes which are particu larly important during the summer months. The Pacific Ocean controls the weather and prevailing west to east air mass movement across western America.. During the winter, the offshore subtropical Pacific high pressure cell migrates south and its oceanic swirl moves south-west. Removal of this high pressure zone allows migratory low pressure cells known as cool, moist Pacific air masses generated along the British Columbian coast to move southward either along the coast or inland usually across Oregon and Northern California. Periodically they extend south to southern California during the Winter. Occasionally Tropical Pacific type air masses generated between Hawaii and southern California, invade the region. In most winters not more than one or two major storms are identified as being this type but eight were recorded in 1941 and a similar number in 1969. This warm, moist mari time Tropical Air mass can also bring warm periods to southern California in winter if only a weak stationary seasonal hiigh pressure develops over the Colorado Plateau because of unseasonal warm temperatures over that region. 40 The northward migration of the subtropical high pres sure belt in summer toward the California coast 'blocks off1 the movement of Polar Pacific air masses which pass further north. Westerly winds descend near the coast and adiabatic compression causes increasing high pressure, higher temperatures and low humidity. The extreme con tinental heating over the California and Arizona deserts may draw in the tropical air from the Gulf of Mexico and Gulf of California which can cause summer thunder showers during the late summer. This effect is more pronounced in the Salton Trough and San Jacinto Mountains but does account for some occasional slight summer rainfall at Beaumont and other mountain stations. Surface winds reflect these air mass movements and greatest variation occurs in the winter as frontal masses move across the area. During the summer westerly and southwesterly winds predominate varying between 3.0 and 8.9 mph (4.8 and 15.8 kph). A northeasterly wind locally known as the "Santa Ana Wind" can become very important. A "Santa Ana" condition in the early Fall results from ex treme continental heating and cooler ocean conditions. As the wind travels southward over the mountain slopes it is warmed by compression. Relative humidity may fall to less than five percent and valley temperatures rise abruptly. This condition of low humidity, high temperature, variable 41 wind speeds often in excess of 30 mph (48 km) and tinder- dry vegetation after the summer drought results in in- . creased fire hazard. Santa Ana conditions can occur at other seasons and in winter can draw in cold Polar air. Rainfall Rain occurs on only 10 per cent of the days in an average year. January, February and March have the greatest number of rainy days. Rainfall varies over the upper Santa Ana Valley and increases to the north as height and mountain proximity forces air masses to rise and cool. Rainfall also decreases eastward as distance from the ocean increases. These two trends are shown by comparing Riverside and Corona, at approximately the same elevation, and San Bernardino adjacent to the mountains (Appendix I, Table 7). The average yearly rainfall for Riverside is 11.96 inches (30.38 cm) while Corona, closer to the ocean, has a rain fall of 13.54 inches (34.39 cm). San Bernardino, although 18 miles (29 km) further inland is approximately 200 feet (62 m) higher and 44 percent wetter with an average annual rainfall of 17.5 inches (44.45 cm). Similar trends are reflected by other local weather stations (Appendix I, Table 9). The wettest year since records began in Riverside 42 (1881) was 1884 when 26.34 inches (67 cm) of rain fell during a calendar year. Other wet years have been 1941 with 22.00 (56 cm) inches, 1945 with 20.99 (53 cm) inches, 1938 with 19.33 inches (49 cm) and 1969 with 21.25 inches (54 cm). The heavy rainfall of 1941 is particularly signi ficant because it occurred in the middle of a wet cycle which broke a major drought period from 1917-1932 (Thomas, 1962). The wettest period of this century was then fol lowed by a drought period (1945-51) during which occurred the driest year since records have been maintained, 1947, with only 3.67 inches (9.32 cm) of rain. These same trends are reflected by comparing other valley stations (Appendix I, Table 10) . During dry years such as 1975, there is normally no rain from late April to late October and the rain is con centrated in the three month period February-April. In wet years, such as 1980, rain may extend into late May but annual variations in rainfall reflect spatial distribution and elevation in the valley. Rainfall graphs drawn for Los Angeles (Lynch, 1931; Thomas, 1962) show an alternation of wet and dry periods generally of 20 to 13 years duration. Dry periods occurred between 1870-1879, 1894-1904, 1917-1932 and 1945-1951. Diaries of early missionaries also indicate dry periods occurred between 1793-1809, 1822-1832 and 1843-1859 (Tho 43 mas, 1962). Short-term climatic fluctuations as described for the last 200 years can lead to valley erosion and de position (Barsch and Royse, 1972). Evidence from glacial deposits (Sharp et al. , 1959)', geobotanical evidence (Axelrod, 1958) and many landslides 14 dated by C as active 18,000 years B.P. (Stout, 1969) indicate that the late Pleistocene climate was probably twice as wet as today. The southward shift of the off shore Pacific high pressure zone would have allowed for the intensification and increase of Polar air masses moving south along the coast from British Columbia during the winter (Lamb and Woodroffe, 1979) . The change in hemispheric thermal patterns as ice barriers developed in the mid-continent would further intensify the storm pat terns on the west coast and increase rainfall. The major change at the Pleistocene/Holocene boundary to one of drier and possibly warmer conditions would cause a marked vegetation change and runoff potential. Increas ing aridity would restrict pine forest to higher eleva-. . tions and replacement by chaparral and at lower elevations Coastal Sage Scrub. Aridity throughout the desert south west increased by about 50% starting approximately 8,000 years ago (Davis,. 1978; Van Devender, 1977). as winter rainfall decreased accompanied by a mean annual tempera ture increase of approximately 3°C. This climatic warming 44 known as the Xerothermic continued until 5000 B.C. Cooling is indicated until 600 B.C. Folklore indicates climate was warmer than the present (Lynch, 1931). This was fol lowed by a marked deterioration in climate which continued until the 1850's. This period is known as the "Little Ice Age" and caused alpine glacier advances throughout the northern hemisphere. Since 1850, the climate has been warmer, but marked by fluctuating rainfall (Lynch, 1931). Hydrology In fluvial systems, changes in discharge and the ability of streams to aggrade and erode their courses are closely dependent on the climate of the catchment area and the amount of sediment supplied from the hillslopes. The Davisian School (Davis, 1909) considers that an ap- . proximate equilibrium exists between stream and hillslope morphologies, while other workers emphasize that stream networks, floodplains, hillslopes and fluvial beds are adjusting over a period of years in response to changes in interdependent varibales (Leopold et al., 1964; Schumm, 1975). These variables include climate, base level changes, tectonic uplift, natural vegetation changes which reduce ground cover, increase hillside erosion po tential and human activities including farming, deforesta tion, irrigation, floodwater control and urbanization. 45 Conditions which activate these variables vary in span and magnitude affecting regional and local conditions at dif fering ratios. All of these factors have operated in the Riverside-San Bernardino area. No river discharge measurements exist for the Santa Ana drainage basin prior to extensive agriculture. Mea surements in the late 1800's when population was lower, flood control had not developed and percolation effects had not been drastically altered by street runoff, more closely reflect the relation of stream flow to climate (Appendix I, Table 11). Irrigation canals bringing water from the local mountains and diversion of the natural river flow began in the 1860's. The citrus industry and truck farming both demanded extensive irrigation and pumping systems which added a significant amount of water to the Santa Ana River during the summer. Measurements of monthly discharge made periodically during the summers of 1888 through 1892 at Riverside Narrows (Lippincott, 1902) can be compared with data col lected for the Rivermaster Reports during 1975 and 1976. In 1888, a year of average rainfall, discharge was lowest in August and was approximately one-third that of present day flow which is maintained in the summer by irrigation, effluent and flood control releases (Appendix I, Table 11). Trends of increasing discharge in the following years re 46 fleet a period of increasing rainfall which broke an eight- year drought from 1876 to 1884. The unusually high runoff in 1892 may reflect the antecedent effects of this wet period which had caused a major flood in 1891 and the addi tion of irrigation water (Figure 4). The effects of man can easily be seen in modern data where discharge remains high and almost constant, compared with early data, throughout the summers. The effects also of a tropical summer storm produced "instant" storm floods increasing the monthly average by five times and resulting in a storm flow of 2,868 cfs. on September 11, 1976. Complete yearly records exist for the five-year period 1896 to 1901 taken near Warm Springs, two miles above the mouth of the Santa Ana Gorge east of Redlands. The seasonal variation of stream discharge is related to seasonal rainfall patterns but additional peaks are offset by the addition of water in the late spring, April and May, from snow melt (Figure 5). This is particularly noticeable during 1899-1900 which was an exceptionally dry season. The double peak also reflects rainfall maxima and snowmelt in 1896-1897. The amplitude of the hydro graph is less than that of rainfall reflecting the addition of infiltration during the rainy season and returning base flow during the dry season. Precipitation during the sea sons 1886-1887 and 1900-1901 were about normal, but des- 47 FIGURE 4. Santa Ana River flood records and tation records for. San Bernardino., Rainfall data corded from the city of San Bernardino. precipi- is re- RAINFALL AND FLOOD RECORD SAN BERNARDINO V A L L E Y SANTA ANA RIVER ----30 20 1629 200,0 0 0 c o ° 130,0 00 c CD o > O JCZ w 100,000 Q 50,0 0 0 49 FIGURE 5. Comparison of yearly discharge patterns before extensive flood control (circa 1900) and the present. 1899-1900 1974-75 Season 1896-97 1979 -8 0 Qmax / Qmin Total Rainfall (in) 16.74 8.64 13.49 30.93 S 101 N I D [ J I F | M | AIM | J |j |a S 0 N D J F IM A IM J C n O 5-1 pite the intervening years of 1888-1889, reflect the in fluence of irrigation runoff. Discharge is usually greatest in February but although the five-year mean in dicates minimum discharge is August, on a yearly basis this may fluctuate between August and September. Under natural conditions the Santa Ana River probably flowed most of the year between the mouth of the Gorge and Riverside although in extremely dry years the stream bed was probably dry in the late summer and early fall. Flow probably was helped by many natural springs or cienagas along the foothills and early writers record artesian flow in various parts of the San Bernardino Valley. Lytle Creek was a permanent stream and Indian settlements and the Spanish ranchos were established around these natural springs* These cienagas are now inactive and stream flow is intermittant. Mendenhall (1905) recorded water table low ering in wells from 5 to 49 feet (1.5 to 14.9 m) between 1900-1904 and between 1904 and 1936 some wells have dropped another 200 feet (61 m) (Dutcher and Garrett, 1963) and this trend continues. The Riverside Narrows ia a unique area long the Santa Ana River as it is one of perennial flow. Between San Bernardino and Colton subsurface flow encounters a geo logic feature known locally as the "Bunker Hill Dyke." 52 This subsurface geologic structure is a zone of impermeable clay gouge along the San Jacinto fault which impounds sub surface flow and causes groundwater to rise on the up stream side. Springs also occur along the west bank of Lytle Creek along the edge of the Rialto Bench. Ground water flow is also restricted in the Riverside Narrows by the granite walls of the Narrows. The depth to bedrock at the northern end of the Narrows does not exceed 100 feet (31 m) (Dutcher and Garret, 1963). The Jurupa Ranch, the original Spanish Land Grant in the area, probably used this section of the Santa Ana as its constant water supply. The velocity of flowing water is dependent in part on discharge and increases proportionally to discharge for any given channel. Slope, depth, width, roughness and channel morphology adjust to transport the load derived from the drainage basin. Competence, the ability to move large sediment particles increases from 32 to 64 times by doubling velocity and the capacity to carry sediment load is increased by an order of 8 to 16 times by doubing velo city (Strahler, 1971). Although there is a tendency towards equilibrium in fluvial landform construction it is not necessarily the mean hydrologic condition that determines the morphology of the fluvial landforms. Instead, the periodic, high in tensity, short duration events such as a bank full flood 53 discharge controls the equilibrium mode. The period of time that separates different modes of operation within a landscape system is known as a threshold (Bull, 1979) and can produce complex interactions within a total system as other variables respond to changes. The historic record of extreme flods, drought and rainfall is summarized in Figure 4. Floods of great mag nitude have occurred in 1969, 1939, 1916, 1891, 1884, 1887 and 1862. The most extreme flood to occur during the period of reliable measurement is 1938 (Troxell, 1942). Devastation from this flood resulted in the total re-evalu ation of flood control along the Santa Ana River and inten sive building of flood protection schemes in the following decade. The high water mark of 1938 flood stands at 820.2 feet (270 m) at Agua, Mansa to the east of the Riverside Narrows (Sidler, 1968). This flood destroyed Hamner Bridge and caused severe damage in the area. But this flood was exceeded by a flood over three times the magni tude of the 1938 flood on January 22, 1862. Intensive de forestation of the San Bernardino and San Gabriel foothills had occurred after sawmills were built in 1845. Gold was also discivered in Holcomb Valley near the crest of the San Bernardino Mountains in 1859. Estimates indicate 1400 people had moved into Holcomb Valley by 1861 causing 54 extensive deforestation of a critical watershed area on a tributary of the Santa Ana River. "But in January, 1862 long continual, warm rains followed an exceptionally heavy snow fall in the mountains, and the fast melting snow swelled the waters of the Santa Ana and its tributaries into a flood that came upon the settlement unexpectedly. The waters from the vast drainage area found themselves forced into a narrow channel, and just above Agua Mansa the river filled the entire valley from the bluff, reaching almost to the little church. (Beattie, 1938). The adobe church has long since gone but positive identification of the location of marble steps entering this church to which the water rose, both in 1937 and again in 1967, established that flood level rose 5 feet above the 1938 level. Computations by the U.S. Geological Survey established the discharge as 317,000 cfs.with a river slope of 0.004 ft per foot (Sidler, 1968). The original work in 1937 also recognized that "the Santa Ana River opposite Colton has silted up five or six feet within the past forty years" (i.e., since 1897). These events of great magnitude establish the floodplain of the Santa Ana within the Riverside Narrows as being the total width of the narrows. Preservation of bedforms in a fluvial system are also dependent on the effects/non-effects of reworking of sedi ment and the establishment of protective vegetation. 55 ORIGIN OF THE NATIVE VEGETATION California occupies 4 percent of the landmass of the continental United States yet it possesses over 5,000 native plant species. Approximately one third of this flora is endemic to California. The flora reflects a mixture of plants adapted to temperate northern climates and a xeric southern Mediterranean climate. The growing season occurs between January and early May. The charac teristic schlerophyll, broad leaf evergreen vegetation is adapted to summer drought, periodic fires and limited winter rain. Geobotanical evidence reviewed by Raven and Axelrod (1977) shows that the present vegetation reflects the in fluence of three geofloras during the Tertiary: neotropical Tertiary geoflora; Arcto-Tertiary geoflora and the Madro- Tertiary geoflora. The Madro-Tertiary geoflora developed and migrated north from the Sierra Occidental of Mexico as a response to increased drought after the Eocene. Dominated by thorn forest and schereophyllous vegetation it replaced the neo tropical broad leaf tropical rainfall and subtropical Savanna geoflora. It was characterized by live oaks, pinyon, pines, Arctostaphylos (manzanita), Berberis, Ceanothus and buckthorn (Rhamnus sp.). These are the an cestors of today's chaparral community. Some species de 56 veloped which have since been restricted to the California islands e.g., Lynothamus (Catalina Ironwood), reflecting the beginnings of more extreme Mediterranean climate in land, offshore cold currents and greater topographic di versity from the beginning of the Pliocene. Increased precipitation and decreased temperature during the Quaternary resulted in the descent of forests to lower levels during the cool-moist glacials and south ward migration of redwood forests. The warm-dry inter glacials created special ecologic relict islands as plants could not adjust to rapid climatic and tectonic changes. The rapid warning trend at the Pleistocene/Holocene boundary and the intense, dry Xerothermic between 8,000 and 5,000 B.C..enabled desert taxa to reach the coast re sulting in numerous disjunct species presently found in the Santa Monica Mountains (Tim Thomas, pers. comm.) and Santa Ana Mountains (Howell, 1929) which are normally associated with the creosote bush and Mojave Desert plant communities. This intense dry period is also associated with the extinction of many large grazing animals, mass migration of hunters, changing socio-economic tribal cus toms, and evaporation of pluvial Pleistocene lakes in the Basin and Range Province., (Davis, 1978) . HOLOCENE PLANT COMMUNITIES A plant community is used by Munz and Keck (1959) to 57 determine "each regional element of the vegetation that is characterized by the presence of certain dominant species." They consider a community to be floristically determined and may be discontinuous with parts of the community forming islands within another or dovetailing with other communities especially in areas of low relief where aspect becomes important. This does not occur in the area*studied but within the community it was found that some species do respond to aspect and are important in understanding the morphology, weathering phenomena, and soil characteristics of some slopes. Two distinct natural plant communities occur, in the area. Coastal Sage Scrub and Riparian'Woodland, and a third, Valley Grassland, is described from isolated remnants and written records of early settlers which imply that it was once extensive. A fourth community, the Southern Oak Woodland, was also very extensive but is now almost non existent. The destruction of these latter two communities may have been important in increasing erosion during the 1860's and 1870's in this area of California as European weeds were introduced, agriculture and citrus faming be came important, and irrigation and pumping lowered the natural water table. 1. Coastal Sage Scrub This vegetation type is an association found on dry, 58 rocky and gravelly slopes and may be referred to as "soft chaparral." It is found in the Southern Coast ranges of California mostly below 3000 feet (930 m) and its greatest development is between 500 feet (155 m) and 1500 feet (445 m)*. It is widespread throughout the area on the Riverside Terrace, slopes, inselbergs and disturbed areas. This area is subject to numerous fires and many species are adapted to fire by stump sprouting and prolific seeding (Appendix I, Table 12). Coastal Sage Scrub is a mixture of both evergreen and dry-season deciduous broadleaf, grey-green shrub form vegetation and is the equivalent of the garrique of the Mediterranean area. The plants vary from small shrubs 1 to 4 feet (0.3 to 1.3 m) tall to taller woodier shrubs. The association forms a more open community than chaparral with an average plant density of 2 to 4 feet (.6 to 1.3 m) on lower slopes and 4 to 6 feet (1.3 to 2 m) on higher areas. During the spring and especially after fires many pioneering annuals bloom which die by May leaving areas of bare soil. The introduced European grasses also die by the middle of summer and are subject to grass fires which leaves many areas with a bare, coarse gravelly grus surface which is subject to sheetwash erosion and removal by early rains in November. The indicator-species are sagebrush (Artemisia 59 californica) , white sage (Salvia apiana) , black sage (S_. mellifera), purple sage (S. leucophylla) and wild buckwheat (Eriogonum fasciculatum). Other aromatic herbs and woody plants are found in the community. 2. Valley Grassland This community no longer exists in a natural state in the area becuase the native perennial blue-green bunch grasses of California, needle grass (Stipa sp.), blue grass (Poa sp.) and three awn (Aristida sp.), were quickly destroyed by livestock and competition from European in troduced grasses and annual weeds. These grasslands were periodically burnt by the sedentary hunting and gathering Indians, the Gabrielleno, but no agriculture was practiced until the Spanish missionaries founded San Gabriel Mission in 1771. Juan Bautista de Anza camped on March 16, 1776 under cottonwoods along the Santa Ana River near the River side Narrows. (This is .now the site of the Jurupa railway bridge at Pedley.) The following day he built a bridge out of dead trees to cross the Santa Ana River. On this second overland trip through California he was accompanied by Father Pedro Faut, a naturalist, diarist and priest. These translated diaries (Boultan, 1930) record that the San Bernardino Valley was; "most beautiful green and flower strewn prairies and snow covered mountains with pines, oaks and other trees which grow in cold climates." 60 A mission settlement was established near Bunker Hill but was destroyed in the 1812 earthquake. A larger settle ment was established near old San Bernardino and the oldest irrigation ditch was constructed in the valley around 1820 (Mendenhall, 1905). The first cattle ranch, the Jurupa Ranch, covering 14 leagues was ceded to Juan Bandini in 1838. A much larger Spanish land grant of 37,000 acres to Don Antonio Maria Lugo, in 1841, covered the entire San Bernardino Valley and firmly established cattle ranching in the San Bernar dino area (Caballeria, 1902) . This created a major vege tation change introducing annual grasses such as wild oats (Avena sp.), wild barley (Hordeum sp.) and brome grass (Bromus sp.) from Europe and establishing our parched brown summer landscape in a period of 80 years. These plants are invaders which rapidly expand into disturbed and fire damaged areas. They can withstand droughts by producing abundant seeds but under stress of prolonged drought conditions they do not survive and there were cattle ranch failures during the droughts in the 1850's and 1870's. 3. Foothill Woodland This community is associated with the foothills of the San Bernardino mountains but the rare California 61 Canyon live oak (Quercus chrysolepsis) and western Sycamore (Planatus racemosa) in the Jurupa area suggest it did exist in the Jurupa Mountains and La Sierra Hills. These trees were removed as the demand for lumber increased as the area's population grew. These trees all require ade quate water within 30-40 feet (9-12 m) of the surface and many died as the water table began to decline as water was siphoned off into the first early gravity irrigation ditches (1870 and 1878 Riverside Canal; 1881, the Highlands Ditch) and later pumped water was supplied to the Gage Canal in 1888 (Mendenhall, 1905). Artesian water flowed until the 1880's but the introduction of deep pumps has dramatically lowered the ground-water levels to 200 to 300 feet below the land surface (Dutcher and Garrett, 1963). 4. Riparian Woodland This plant community is found along the banks of small streams and the Santa Ana River. It is well developed on the Santa Ana River between the Rubidoux and Prado Dam as in this section rising ground water across underground fault barriers results in perennial flow although this might be drastically reduced in dry years. Beattie (1938) quotes areas in the cienagas (local marshes and river bottoms) where; 62 "growth of trees was so dense that in places it could not be penetrated. Black alders, two to three feet through, willows in abundance, and sycamores four feet in diameter, over which wild grapes climbed to the tops." Beattie, 1938. Today Black Alders and sycamores do not exist, falling prey to the early lumbering industry and drastically de clining water tables. Instead the sand bars and area immediately adjacent to the river are dominated by the Giant Reed, Arundo donax, introduced from Asia in the 1880's, Bidens laevis, (Bur marigold) Schismus barbatus, Melilotus alba (sweetclover) and cattails (Typha latifolia). Young seedlings of willow (Salix lasiolepsi, S. lasiandra and £5. hindsiana) develop within one.year of being exposed on bars and small islands, but reach maximum heights of 10 to 14 feet (3 to 4 m) on low raised terraces within the floodplain. These willow provide shade for seedlings of cottonwood, Populus fremontii, which make up the dominant upper story cover species on higher terraces. VEGETATION, FIRE AND FLOOD Coastal Sage Scrub and Chaparral plant communities are naturally subject to fire because they are resinous and become extremely dry during the summer drought. Fire is also beneficial to these communities which reach an overgrown senile stage after about 20 years which inhibits new growth. Fires under natural conditions are the result 63 of summer lightning but most recent fires are started by arsonists. Plant growth recovers after about five years but as rainfall in southern California is cyclic, superabundant rainfall, unimpeded by soil-protective vege tation can result in abnormal erosion, disastrous floods and deposition of coarse debris on floodplains and alluvial fans. Doehing (1968) and Ursic (1970) found that fire- flood sequence results in accelerated erosion and signi ficantly increased water flow and sediment from watersheds during the winter. These effects might continue for up to five years as even burnt roots initially hold soil but as they decay and new growth is not strong enough to hold steep slopes, steep slopes can collapse and increase stream erosion. Rainfall in southern California can also occur in disastrous short periods of time, for example, Lytle Creek Ranger Station on January 25, 196 9 received 21.61 inches (55 cm) of rain in 24 hours (U.S. Weather Bureau, 1969). This combination of intense, heavy rainfall after major fall fires resulted in floods on Cucamonga e.nd Day Canyon alluvial fans (Singer and Pierce, 1971). Even during the dry season debris movement on a burnt: chaparral area exceeds that on an unburnt area during the wet season, and during the wet season debris movement is 10 to 16 times greater on the burnt areas (Krammes, 1965). 64 The most disastrous flood in the history of the upper Santa Ana occurred in 1862. This coincided with heavy rains, removal of timber from the San Bernardino Mountains and population increases in the San Bernardino area. Not only are fires disasterous but agricultural studies show that a change in the plant community can also initiate soil erosion (Langbein and Schumn, 1958). These studies show there is a ten-fold increase of sediment yield for row crops compared with pastureland when precipi tation is held constant. If scrub type vegetation is equated with row crops and pastureland with grassland and forest (Leopold et al., 1964) , the shift from pluvial to interpluvial and corresponding shift from grassland and forest pluvial conditions to scrubland interpluvial condi tions could lead to dissection at the beginning of this climatic change. The alluvial surface previously protected by the grassland and chaparral woodland would be subject to erosion. Sealevel would still be at a low level while this initial vegetation change was occurring which could also encourage dissection of stable surfaces. The deeply weathered material formed under wet, warm conditions being eroded would also be subject .to increased hazard reflecting the more intense erosion- in a dry-warm xeric climate. CHAPTER 5 65 GEQMQRPHIC AND SEDIMENTARY FACTORS GRANITE WEATHERING The transition from fresh bedrock to weathered bedrock involves both chemical, physical and biologic processes. Granitic rock forms under high pressures (1000 to 1400 bars) and high temperatures (600 to 800°C). Rock emplaced and formed under these circumstances is at a state of dis equilibrium when later uplifted by faulting and exposed by erosion. Granitic outcrops may be found in four forms in the Riverside area; prominent skyline residual tors along the edge of the Riverside escarpment; inselbergs; prominent bedrock steps associated with gently sloping benches; and isolated mid-slope boulders and rock outcrops. Inselbergs are hills rising sharply from the gentle sloping Riverside Grand Terrace. In other parts of the world they are limited to periodically moist, savanna climates. Their formation appears to depend on the marked contrast of seasons; in the dry period, very intensive mechanical weathering occurs, often in the form of rock spalling and possibly due to periodic fires, common during the dry season; in the rainy period, the powerful effect of surface run-off occurs creating sheet flow and removal 66 of spalled material (Hettner, 1929). A savanna landscape is characteristically associated with summer rain and winter drought resulting in open grassland and scattered thorny trees. A Mediterranean climate can produce similar vegetation patterns and also intense seasonal changes. The cooler, moist winters may also intensify deep chemical weathering as mositure is not drawn off by rapid evapora tion. Removal of overburden also encourages horizontal sheet structure (Jahns, 1943). Exposed granite dries rapidly after rain and weathers more slowly than granite covered by overburden. Bedrock Weathering Field observations using the semiquantitative seven weathering classes of Clayton and Arnold (1972, Appendix I, Table 13) were used to give reasonable field estimates of rock strength and weathering factors. Throughout the region most outcrops could be classified in classes 3 through 6. Most commonly rock outcrops were either cate gory 3 and 4, weakly weathered rock and moderately wea thered rock. Class 6, well weathered rock was only seen north of the river where extensive land excavation by bulldozers exposed weathered crumbly grus extending to more than 50 feet (16 m) below the surface. The weathered surface rocks were massive blocks, approximately 10 feet 67 by 6 feet (3 m by 2 m), "floating" on this intensely wea thered grus. This rock had undergone chemical weathering at depth and indicate weathering forms normally associated with more tropical climates (Ruxton and Berry, 1957). Physical Weathering Physical weathering as a singular process distinct from chemical weathering requires recognition of a) physi cal breakdown of the rock and b) lack of secondary mineral formation and grain alteration. Throughout the region biotite was stained by iron oxide and feldspars were opaque when examined marcoscopically. Physical weathering weakens all rocks in classes 2 to 5. In a Mediterranean region this is achieved by hydra- tion-dehydration processes but this process is probably restricted to the top 6 to 10 feet (1.8 to 3 m) except along joint faces. Chemical weathering resulting from hydration and breakdown of the feldspars and biotite by disilication and alumination of these primary minerals (Jackson, 1965). Well weathered rock can be broken by hand into sand-sized particles (grus) and roots can penetrate between the grains. Hydrolysis involves some expansion of the mineral grains. These minute fractures are exploited by physical weathering expansion which increases the rate of chemical 68 weathering. Increased physical and chemical weathering decrease rock hardness and strength. Evidence of spalling through out the region ranged from thin sheets 1 to 3 inches (2.5 to 7.6 cm) thick. Joints are subangular to rounded and filled with grus. An unusual surface pattern on granite boulders where fire has periodically swept through every two to three years are polygonal cracks varying between 5 to 12 inches (12 to 30 cm) in diamter. These cracks extend vertically 1 to 2 inches (2.5 to 5 cm) below the surface and then beneath the crack is a dish-shaped con cave upward plane connecting these cracks. They have only previously been described in the Chiracahuas, Arizona (Leonard, 1929). These structures are most frequently seen on surfaces with a southerly and westerly exposure. Surface granular disintegration of exposed boulders was also observed but his process was not evident when soil was dug away from the boulders. This fire-induced process is probably enhanced by previous chemical and physical weathering (Blackwelder, 1927; Clayton et al., 1979). Fires are frequent in this area during the late summer and autumn under Santa Ana Wind conditions. Most of the area is burnt over every 6 years and many boulders are fire blackened. Fires appear to increase granular disintegra tion but evidence may be rapidly removed by rainwater run 6-9 off and erosion. Biological Weathering Many granitic boulders have patches of the encrusting lichen Lecanora novomexicana on both exposed and unexposed surfaces. This lichen dies back under extreme drought conditions but when growth begins after rain can physically force apart grains and small fractures. It produces hydro chloric acid and chemically disintegrates rock. It was also found growing around the rims of small depressions on flat surfaces which resembled small, dry tidepools. These depressions had been filled with rain water and maximum lichen growth occurred around the pool's high-water mark. The depression floor frequently had a fine silt cover in which seedlings attempted to grow. All of these granite outcrops had a more diverse flora than the surrounding slopes. Granite grus is rich in potassium and the grus filled joints provide natural planters where roots are more protected from summer heat once the plant is established. The roots penetrate between grains, fractures and joint planes and add their expansion force to increase bedrock fracturing and further moisture penetration. SOIL FORMATION ON UPLAND AREAS Immediately adjacent to many skyline tors are soils 70 with an eroded A horizon so that the B horizon may be ex posed at the surface. These soils are characteristic of the Fallbrook series (Appendix III A) but do not have the A horizon associated with this series. These soils with a truncated profile may form a ring approximately 100 yards (91 m) wide around many tors. Truncation may have been initiated by more intense runoff immediately adjacent to the rock outcrops, but is now compounded by vehicular dis turbance (Ruxtan, 1958). Disturbed areas are compacted which reduces the infiltration capacity of soil, and in creases the soil bulk density. This results in increased runoff and erosion during rainstorms (Iverson et al., 1981). Vegetation cover is also reduced or destroyed further increasing the destruction of the surface soils as organic litter is unavailable to form an A horizon, increase pore capacity as roots develop, or protect the soil from further erosion. Frequently, south- and west- facing slopes have been stripped more than north-facing slopes, again suggesting that the lack of vegetation and lower moisture content increases erosion. Three soil series are commonly found associated with the granitic terrain: Fallbrook, Vista and Cieneba (U.S. Department of Agriculture, 1971). These soils are Xeralfs, Ochrepts, and Orthents (Appendix III A, F, E). Their re spective locations suggest that of the five factors affecting soil formation proposed by Jenny (1941), topo graphy appears to be the greatest influence on soil mor phology on the slopes of the Riverside Escarpment. Ero sion rates on the steeper slopes are sufficiently high that other factors, climate, biota and parent material do not allow full expression of pedogenic development with time. Fallbrook Series The Fallbrook Series are well drained soils associated with granodiorite and tonalite. They have developed on the gently rolling uplands into which streams are presently eroding. Slopes range between 2 to 40 percent in these areas. In a typical profile, the surface layer is a brown, sandy loam about 14 inches (35 cm) thick. The subsoil (B Horizon) is a reddish brown sandy clay loam. At depths varying between 24 and 30 inches .(30 and 76 cm) is wea thered granodioite (Appendix II, A & K). Birkeland and Shroba (1974) used the hue of C and B horizons to indicate intensity of oxidation (and hence age) in dating Quaternary Californian soils. The hue progres sion is from 2.5Y to 5Y to 10YR to 7.5Y with time. This hue changes in a progression from yellow to red and re lates to the progressive increase in free Fe20^ content in the soil. 72 The dominant hue of the B horizon in these soils is 5YR and the hue of the C horizon is 7.5YR (Appendix III, A) .. This soil has a well developed argillic B horizon. These soils are found in areas where soil erosion and sheetwash is not so active as on steeper slopes associated with the Cieneba and Vista soils. Immediately adjacent to many tors the A horizon truncation or absence reflects more intense runoff in these areas. These soils overlie deeply weathered bedrock of wea thering classes 5 or 6. However, as recognized in Idaho (Clayton et al., 1979) , the B-C boundaries are more dis tinct than on more weakly weathered rock. Clarity and distinction of soil morphologic boundaries and textures indicates that soil pedogenic processes have progressed over a long period of time. The position of these soils on the rolling upland interfluves which are remnants of older erosion surfaces indicates that in these areas erosion is relatively slow. Vista Soils These soils are associated with both Cienaba and Fall brook soils and occur in two locations; either a) as a soil occupying a broad interfluve, or b) as a soil in midslope locations marked by a major break in slope similar to the stepped topography described by Wahrhaftig in the Sierra 7.3 Nevada (1965). . Vista soils have a cambic subsoil horizon and are less strongly developed than the Fallbrook soils, but more strongly developed than the Cienaba soils. A broad valley, isolated from all other valleys, and now forming a major wind gap in the eastern Jurupas, is covered with soils of the Vista series (Soil Survey Staff, 1971). This plateau is at 400 feet (340 m) and has been interpreted by Morton (pers. comm.) as an erosional feature developed when large fans from the San Gabriels extended across the Jurupa Mountains and into the Perris Block during the mid-Pleistocene. In the Riverside Escarpment two stepped erosion sur faces occur above the Riverside Grand Terrace (T1 and T2). These steps are not extensive. Granite outcrops occur on the front of these steps and vertical and horizontal jointing is prominent. The surface behind these prominent frontal outcrops are almost horizontal or very gently sloping. The Vista soils are found on these surfaces. Erosion is not active on these gentle slopes and a thicker soil profile develops (Appendix III, F) . The granite grus, where exposed in stream cuts, is deeply weathered on these surfaces, but no fresh outcrops provided analysis of joint patterns. Exposed granite weathers slowly compared with buried outcrops and Wahrhaftig (1965) proposed that ex posure of the granite at the front of these steps would act 74 as a local base level and streams develop a trellis pattern to accomodate the exposure of these surfaces. Over a long period of time these develop extensive coalescing surfaces and the stepped topography may be the result of normal ero sion of granite rock on a tilted fault block combined with strath surface development. The development of these surfaces is enhanced by de creased runoff on these gentle surfaces which increases soil moisture and hence soil formation. The lowest sur faces occur between 1100 and 1200 feet (340-365 m) and a higher surface occurs at 1400 feet (425 m). They are more prominent on south-facing slopes where more rapid runoff may enhance formation of the initial stepped front. These steps are not well developed in Pigeon Pass which is the most active erosional valley and is closest to the San Jacinto fault zone. They are prominent along the west facing slope of Mockingbird Canyon and in the valleys be tween Mockingbird and Sycamore Canyon. These surfaces are presently undergoing dissection suggesting that they de veloped during a short period of landscape stability. This process may be intensified by soil and vegetation dis turbance as fires, off-road vehicles and new housing de velopments associated with increased runoff extend into these hilly areas. 75; Cieneba Series These excessively well drained Entisols are found on upland slopes where slopes range from 5 to 50 percent. In a typical profile the surface layer is brown, sandy loam about 14 inches (35.56 cm) thick. Underlying this is light yellowish-brown gravelly coarse sand. At depths varying between 18 and 22 inches (55.88 cm) is weathered grano- dionite (Appendix III, E). The dominent hue of the oxi dized C horizon is lOYRv. These soils are found on steep slopes which are fre quently burnt and subject to erosion. Erosion rates are sufficiently high that climate, biota and parent material are not allowed maximal expression for pedogonic develop ment. Birkland (1974) indicated that the time required for steady state (maximal development) of A horizons ranges from 10 to 1,000 years, (Entisols), for cambic horizons 100 to 10,000 years (Inceptisols) and for argillic hori zons (Alfisols) the range is between 1,000 and one hundred thousand years. Under Mediterranean climate conditions this process may be accelerated, but on slopes which are subject to erosion, except on the broad upper interfluves, soils may never achieve this steady state condition be cause of periodic removal of surface material. 76 GRANITE SEDIMENT The weathered granite grus is the provinance (ulti mate source) material for the coarse sediment found in the streams draining the Riverside area (Figure 6). Settling tube analysis of grus removed from the .weathered surface of the tors and also collected at the base of the tors re vealed that there is a distinct break in the particle size population at the -1 to 0 phi size interval (very coarse sand). Standard grain size characteristics obtained from the moment measures of phi mean grain size (m$), phi stan dard deviation (SD, sorting) and phi skewness (SK$), were used to identify textural changes in grain populations as erosion, transportation, and deposition occurred (Figures 7 and 8) . A series of samples were collected along the Mocking bird Canyon and Pigeon Pass drainage, and from the old alluvium into which the modern stream is eroding (Figures 7 and 8). These were compared with the analysis of the granite grus. McLaren (1981), proposed that transportation of material from the source would result in a total grain size population that was finer and better sorted than the original parent material. In these examples the transportation has produced a finer and better sorted deposit. The parent coarse sand decreases downstream as a result of erosion during trans- 77 FIGURE 6. Location map of sediment samples and drainage basins. * V. - s M l V ernon R oad □ RM 6 -8 X F lo o d P lain - S a n ta A n a R iv e r w m AWD □ RB A D une S a n d O A c tiv e C h a n n e l - P e r r is B lo ck A c tiv e C h a n n e l- S a n G a b r ie l M ts . • G r a n ite G ru s □ O ld A llu v iu m G 14 _ PJIPG^V 32 IML37-38 l S V D t X J 3 9 ^ V """" X T P 4 3 -4 5 Jurupa R ailw a y B rid g e S46-47, Pe 23-27 > 6 2 7 -2 8 P e d ,e y PeT29-3l Road H am ner B rid g e ,M35 M22gp M2I \M20 sM1 6 GI5 117° 30' 7 9. FIGURE 7. Comparison of textural parameters for granite grus and Mockingbird Canyon sediments. LAG m- Coarser SD- Poorer Sk- Positive s5 4 0 - \- X o 2 0 - UJ £ -2 0 2 MOCKINGBIRD DRAINAGE A C T IV E C H A N N E L 4 0 20 G R AN ITE GRUS G 15 ma0.30 SD*I.89 Skaff.09 K=l.45 2 - MI8 ma0.50 SDa 1.92 Sk=O.I4 Ka 1 .5 1 tU, -2 0 2 4 0 20 EROSION ■0 M 17 ma0.03 SDa2.05 Sk=0.3l p. Kal.33 -2 0 TRANSPORTATION 4 0 TRANSPORT m- Finer SD- Better Sk- Negative 20- o M 3 6 mal.07 SDal.79 Sk=0.96 K=3.00 -2 0 2 4 OLD A L L U V IU M No. Facing Slopes M 19 ma0.95 SDa 1.72 SkaT.2l K=3.I9 n i M 16 m a 1.66 SDal.58 Ska 1.17 Ka5.08 to -2 0 2 a WEATHERING M 2 0 msl.25 SDal.63 SkaT.I5 K=3.9I - 2 0 2 4 MODIFICATIONS M 21 mal.l2 SDa 1.68 S k«l24 K=3.59 -2 0 2 4 - 2 0 2 4 So. Facing Slopes GRAIN SIZE IN PHI UNITS WEATHERING m - Finer SD- Better Sk-Strongly Negative co o 81 FIGURE 8. Comparison of textural parameters for granite grus and Pigeon Pass. PIGEON PASS DRAINAGE A C TIV E CHANNEL 4Ch X 2 0 - O Id 5 4 0 -i 20- GRANITE GRUS.aP‘ o-J 4 0 - , m= 0 .3 0 SD«J_.89 Sk= 0 .0 9 K= 1.45 20- oJ 6 O- 1 TRANSPORTATION 4 0 - TRANSPORT m - Finer S D- Better 20- Sk- Negative o -i P 32 m= 0.28 SD= 1.91 Sk= 0.53 K= 1.76 -2 0 2 4 P WEATHERING a ■p ms 1.71 SDs 1.57 Sk=T.59 K=5.44 -2 0 2 4 a P 13 m= 1.43 SD= 1.30 Sk=^.09 K= 7.35 OLD ALLUVIUM P 9 m=O.I7 SD = 2 .24 Sk=O.OI K -I.I6 m -2 0 2 4 ■fl PIO m=0.47 SD= 2 .4 4 Sk= 0 .2 0 K= 1.44 -2 0 2 4 -2 0 2 WEATHERING m - Finer S D - Poorer GRAIN SIZE IN PHI UNITS 00 t s j 83 portation but the initial size gap imprinted onto the sediment in the -1 to 0 phi size remains throughout the length of the stream. Samples from the old alluvium also have this same characteristic, but have a lower percentage of coarse sand. Median diameter is finer than present day sediment, but sorting varies little from present day stream deposits. The finer grain size could reflect a) weathering in situ, b) derivation from a sediment which had undergone more deep weathering before erosion and transportation occurred or c) a different paleohydrologic regime for these older alluvial deposits. This case illustrates that sediment characteristices imposed upon sediments become definitive limits for modi fication of that sediment. These sediments are all nega tively skewed indicating that both the old alluvium and modern stream deposits were all deposited and have under gone no further selective deposition except in the case of the older alluvium. Here weathering has occurred but this is a modification which is not imposed by further transpor tation (Figure 7). This process can also be illustrated by plotting stan dard deviation and sorting parameters (Figure 9). The older alluvium collected from many Riverside,localities has a distinct population which can be distinguished by its finer texture and better sorting than ^granite grus. Ma- 84 FIGURE 9. Sediment sorting and population distribu tion of Santa Ana River and tributaries. The following letters represent the localities and environments shown on Figure 6: J, Jurupa Railway Bridge; L, Lytle Creek; M, Mockingbird Canyon; ML, Mira Loma Wash; P, Pigeon Pass; Pe, Pedley Road; RB, Rialto;Bench; RM, Riverside Mesa; S, Schleisman Road (Day Canyon Wash); V, Mt. Vernon Road; W, Wisconsin dune field (Sand Hills); B, stream bank; C, channel; D, dune field; G, granite grus; T, terrace. ♦100-1 ♦2. 00- ♦ 1 . 0 0 - H CO CO Ul z 0.0- * Ul X w -i. o o h -2.00— -3 .0 0 — 1 V 3 iv4 PeT3l X pe28A X J T 4 2 w P.T27AP ^T29 M L 3 7 ^ B W X J T 4 4 J T 4 0 X X P e T 2 6 | X J T 4 3 M L 38 © S 4 7 □ RB "GI5« O M I8 M 36 0 O M I7 O P 3 2 J T 4 5 M I6 _U £ E « M 3 5 B a0 M2I M 20 M I9 J 3 9 . X P e 2 4 v x V5 X \ X J 4 0 Pe23 >fc@ LC G V 2 © P I I P I3 © X P «25 X S an ta A na R. F lo o d P lain A Dune S an d 0 C hannel - P e rrle Block O Channel - S a n G a b rie l M te e G ra n ite G ru e □ O ld A llu v iu m • P 9 0 - 0 RM 7 J 3 R M 8 □ PIO PI2 O P 3 3 .20 : -40 .60 : Very Well So jwell So Mod Well: t So : .80 Mod So T~ 1.0 1 . 2 1.4 Poorly 1.6 1.8 2.0 T 2.2 2.4 So V. Poorly So STANDARD DEVIATION co L n 86. terial transported from the granitic terrain underlying the Perris Block is a linear population representing better sorting as grain interaction reduces the overall particle size producing a better sorted deposit. The population is still strongly bimodal as illustrated in Figure 9. DRAINAGE BASIN MORPHOMETRY Morphology of drainage basins reflect climate, vege tation, soil characteristics, topography, permeability of bedrock and adjustments to gradient charge. The three, drainage basins studied, Pigeon Pass, Sycamore/Tequesquito Arroyo, and Mockingbird Canyon, lie with increasing dis tance from the San Jacinto fault zone (Figure 8). The first two drainage-basins are tributaries to the Santa Ana River and have maintained their courses to the Santa Ana by recent entrenchment of up to 100 feet (31 m) along Teques- quito Arroyo (Figure 6). By contrast, the drainage from Mockingbird Canyon terminates on the Riverside Grant Ter race and today a large earth dam catches water from this drainage basin. Previously, a small intermittent stream drained west through the Arlington Gap into Temescal Wash. (Data from drainage basin analysis is presented in Appendix II, ) Three factors, climate, natural vegetation (coastal sage scrub), and granitic bedrock, are similar for these 87 basins. Each basin is also markedly asymetric with the north-facing slope being steeper than the south. This, is associated with significantly reduced overland runoff in a Mediterranean climate where a large amount of ran can fall in a short period of intense rain. A thicker soil sequence on north-facing slopes and also there is a vegetation dif ference. Dry south-facing slopes are predominently cov ered with extreme drought adapted Artemisia California, Encelia farinosa and Salvia apiania (white sage) and have thins soils. North-facing slopes which retain soil mois ture for a larger period are characterized by Salvia. . . mellifera (black sage), (Encelia californica, Nicotiana glauca besides Artemisia californica. Valley asymetry has been recognized in California by Emery (1947) and Melton (1952) and analyzed using slope length and orientation parameters. They found that the north-facing slopes are often steeper and shorter than slopes with a southerly exposure. These north-facing slopes often develop thicker soil profiles and accumulate more colluvium than the drier, south-facing slope. In each drainage basin studied two north- and two south-facing basins were also analyzed to determine if valley asymetry, recognizable in the field could also be studied using statistical drainage basin morphometry parameters and tech niques . 88 Morphometric Parameters Horton (1945) , proposed certain laws of drainage com position which assume an orderly development of the geo metrical qualities of insequent drainage systems. These drainage basins were analyzed for conformity of these watersheds to the laws of drainage composition. The streams were ordered after Strahler's adaptation (1952) of the Horton (1945) scheme of classification. In this adap tation, small finger-tip tributaries are designated as order I. Two first-order streams unite to form a second- order segment, and a third-order segment is only created at the junction of two second-order streams, and so on. The master segment is always a segment of the highest order. A basin is designated as the same order as the master-stream segment. In addition to his pioneering work on stream ordering Horton (1945) showed that there is a close relationship between the numbers and the length of streams of each order when compared with the order value. The first law of drainage composition (the law of stream orders) was stated by Horton (1945, p. 291) to be: "The number of streams of different orders in a given drainage basin tend closely to approxi mate an inverse geometric series in Which the first term is unity and the ratio is the bifurcation ratio." The second law (the law of stream lengths) given by Horton 8 9 (ibid) was: "The average lengths of streams of each of the differing orders in a drainage basin tend closely to approximate a direct geometric series in which the first term is the average length of streams of the first order." The bifurcation ratio is the ratio of branching in a drainage network; ratio of number of streams of order u to the number of streams of the next higher order. Mathe matically Horton's law is stated as: Nu = (s - u) Where Nu is the number of streams of order u, is the bifurcation ratio, s is the highest order within a drain age network, and u is the order of basin or stream seg ment denoting the level of magnitude in the drainage net work hierarchy. Mathematically this is written as: Su = LiR (u”1) J L i where Ln is the mean length of stream channel segments of order u, RT is the stream length ratio, ratio of mean J L i length of streams of order u to mean length of streams of the next higher order. Horton found that these morpho- metric characteristics have a regular relationship with order, such that when graphed on semi-logarithmic paper the points lie on a straight line. Horton (1932) recognized that the density of the stream network is a sensitive parameter which may provide 90 the link between the form of a basin and processes acting along the stream course. Horton defined stream density as the length of streams per unit of drainage area. It is generally expressed D = £L/Area, in terms of miles per channel per square mile. Stream frequency (Fs) was also proposed by Horton (1945) as a measure of the number of stream segments per unit area and is therefore dependent upon stream order whereas drainage density is independent of order and con siders the whole basin. Stream frequency indicates the intensity of drainage dissection and vegetation controls. Drainage density is a function of runoff intensity, ero sion potential, relief, pedologic, lithologic and vegeta- tional controls. This data was compared with similar measurements in the Verdugo Hills (Smith, 1950) and the San Gabriel mountains (Bauer, 1980; Maxwell, 1960) of southern California which have experienced similar tec tonic events, are underlain by granitic and metamorphic rock complexes and all experience the same Mediterranean climatic controls (Appendix II; Table 17). Water and sediment yeilds are strongly influenced by the length of water courses per unit area and drainage density is the response of the total drainage basins to these factors. The computer program designed to fit the data to linear fits used the method of least squares (Young, 1962). 91 The resulting parameters of this analysis are functionally related to the bifurcation ratio and stream length ratio. Calculated at the same time, the variance of the sample for the linear fit was calculated for each linear fit (op. cit., p. 122). The variances of the linear parameters were also computed (op. cit., p. 122). The variances for the two parameters of the Horton theories were then com puted using the standard techniques used in propagation of errors (op. cit., p. 99). This data is presented for all drainage basins utilized in this study in both graphical and tabular form. In addition to the indices of drainage-network compo sition based upon stream orders other important geomorphic considerations are relief, drainage pattern, and the stage of geomorphic development. Relief is analyzed by a relief ratio, defined as: "The ratio between the total relief of a basin (elevation difference of lowest and highest points of a basin) and the largest dimension of the basin parallel to the principal drainage line" (Schumm, 1956). This re lief ratio allows comparison of the relative relief of any basins regardless of differences in the scale of topo graphy. Drainage patterns are usually expressed in quali tative terms and the categories used in this study are those of DoornKamp and King (1971). Throughout this study south-facing slopes are labelled 92 A and B and north-facing slopes are called C and D. In all cases A and C are closest to the headwaters of the drainage (Figures 10, 11, 12). Data from these small drainage may also reflect changes in stream length as river capture, headwater extension and retreat of the basin divide maintaining steep gradient at the valley head have occurred. Drainage Density Drainage density is derived from two variables, namely basin area and total stream length. Water and sediment yield are influenced by the length of water courses per unit area. It is also the characteristic which reflects the amount and rate of input/output from the drainage system. Attempts have been made to relate drainage den sity to climatic inputs. It has been proposed that drain age density increases as mean annual precipitation in crease ^Williams and Fowler, 1969) , rainfall intensity in creases (Chorley, 1957) , and runoff intensity increases. These factors also reflect infiltration capacity, soil strength, vegetation and percent bare area of soil. In a regional scheme it is considered that drainage density re flects precipitation intensity but local variations are accounted for by the latter variations including land use. On the world scale it has been found that the highest 93 FIGURE 10. Pigeon Pass drainage network. PIGEON PASS DRAINAGE BASIN 1 --------*— M ountain Front Minor B a tin M a rg in s I mile I kilometer BLUE MOUNTAIN ' V-W* y 'B O X S P R IN G S M O U N TA IN S 95 Sycamore/Tequesquito drainage network. FIGURE 11 SYCAMORE/TEQUESQUITO DRAINAGE BASIN Mountain Front Miinor B a tin M arglnt 97 FIGURE 12. Mockingbird Canyon drainage network. MOCKINGBIRD CANYON DRAINAGE BASIN Mountoin Front Minor B atin Morgin* VO 00 99 drainage densities are accounted for in semi-arid areas of Australia and the western U.S.A. The overall range of drainage densities for areas with a Mediterranean climate is between 6 and 25 (Gregory and Gardiner, 1975). The range of data from this study is between 15.01 and 16.48 for the three main drainage basins (Appendix III, Table 14), but ranges between 14.13 and 27.27 for fourth order tributary basins (Tables 15 and 16). This is comparable with other data from southern California where Smith (1950) found a range of 15.20 to 34.50 and a mean of 17.5 for the Verdugo Hills. In the San Gabriels Bauer (1980) found a range of 11.32 to 24.62 and a mean of 17.43 (Table 17). Detailed analysis of the three basins (Tables 18, 19, 20) reveals that in each basin the south-facing slope has a greater drainage density than the north-facing slope. The exception to this is drainage basin A9, Sycamore Can yon, but this particular stream's drainage has been re cently captured by piracy (Figure 11) and reflects a lower drainage density related to an earlier drainage system south across the Perris Surface. Except for this one case the drainage of the minor tributaries is also steeper than the main drainage as these are the sites of active head ward erosion. Pigeon Pass drainage basin also has the highest overall drainage density. This is the smallest 100 basin and also the basin closest to the San Jacinto fault. Headward erosion has captured one stream which previously drained south across the Paloma Surface. When considering the mean values and the range of values for north- and south-facing slopes the north-facing slopes have a lower mean value and a narrow range of values than south-facing slopes (Tables 15 and 16). The main drainage basins have a typical dendritic drainage pattern but a difference can be recognized between north and south-facing slopes especially in Mockingbird Canyon (Figure 12). The south-facing slope has a parallel drainage pattern compared with the north side. This may reflect the preferential erosion of a dominant joint pat tern in the granitic terrain. Drainage density is also a measure of the ability of a soil and vegetation cover's water holding capacity. A shallow soil typically results in more rapid runoff than soils with a thicker profile. Soils on south-facing slopes are significantly thinner than on north-facing slopes (Tables 15 and 16) and the alluvial fill generated on the north-facing slopes is also greater. North-facing fill along Mockingbird Canyon varies from 14 feet (5 m) at the valley head to 120 feet (37 m) near the canyon mouth but is only 80 to 100 feet (25-31 m) at the mouth of the Canyon on the south side. Second and third order 101 streams are more deeply entrenched in this alluvial fill on the north-facing slopes. If the soil is not thinner on the south-facing slopes as is the case in Pigeon Pass it differs drastically from the north-facing slope by the presence of a silica duripan. These silcretes form resistant horizons beneath the allu vial fan surface and streams are entrenched within deep narrow valleys on the upper fan surface. The relationship between drainage density and height values expressed as the relief ratio is of interest. In Pigeon Pass, the relief ratio is higher than in all other basins and this basin also has the highest density ratios (Appendix'll, Table 18). Significantly, although the north-facing slopes are steeper, they do not have the highest drainage density suggesting again the importance of vegetation and soils. The south-facing slope of Sycamore Canyon, has the lowest drainage density of all basins analyzed (A9, Table 19), even though this drainage extends into the Box Springs Mountains which rise to over 2,600 feet (806 m). This drainage originally drained south onto the Paloma Surface and has been captured by headward erosion of streams draining into the Santa Ana River. This area is also one which is frequently burnt. Two wild fires occurred in this area during the field season from September 1980 to 102 June 1981. Fortunately 1981 was an extremely dry year and except in one area, no appreciable erosion was noted. Recent extensive building may be reactivating some first- order stream courses increasing drainage runoff and de creasing areas where ground water can percolate into the soils. Bifurcation Ratio Strahler (1964) recognized that in drainage basins where structure does not exercise a dominant role in drainage development the bifurcation ratio is between 3.0 and 5.0. The bifurcation ratio relates the number of streams of order n to the number of streams of the next highest order. Only in the main drainage of Mockingbird Canyon does the bifurcation approach 5 (4.37) and may re flect the presence of the Mockingbird Canyon Fault in part of this drainage basin. This does not appear to in fluence the minor drainage basins. In graphic form (Fig ure 13), the north-facing slopes more cloesly approach slope and log plot of the main drainage when plotted on semi-logarithmic paper. Again this correlates with relief and the greater total number of streams of the north-facing slopes of this basin. This also applies to the north- facing slopes in Sycamore and Pigeon Pass. When consid ering the overall basin characteristics of the 4th order 103 Graphic presentation of bifurcation ratio. FIGURE 13 LAW OF STREAM NUMBERS 104 SOUTH FACE — O C NORTH FACE SYCAMORE/ TEQUESQUITO PIGEON PASS IOQ _ X log N = 3.51-.579 U log N = 2 . 9 8 - .5 0 9 U tO IQ _ MAIN DRAINAGE MOCKINGBIRD IOQ. _ BASINS = 3 . 7 4 - . 6 4 0 U - log N IQ- ORDER 105 basins (Table 15 and 16), the range is narrower for south- facing slopes, 2.49 to 2.78, but the overall mean is also less for these basins when compared with north-facing slopes (2.52 compared with 3.10, Table 13). Considering just the main drainage basins (Figure 13, Table 14), the bifurcation gradient is similar for both Pigeon Pass and Sycamore Canyon. Sycamore Canyon has an extremely good fit of data with all data points lying within three percent of the linear best fit regression line. Fit is more variable within the Pigeon Pass drain age and the large number of first-order streams suggests headward increase of drainage without corresponding growth and balance in the higher orders. Mockingbird Canyon drainage has an extremely good fit of the data points ex cept at the fifth order. This may indicate that these drainage basins were in grade to an earlier phase of basin erosion and the basin has not adjusted to recent drainage changes because these occurred after Mockingbird was no longer part of the active Santa Ana drainage scheme. Mean Stream Length Stream length data reveals the characteristic size of the various components of the drainage network. They form the unit cell and the building block for the drainage basin. The mean length of channel segments of each of the 106 successive orders of a basin is greater than that of the next lower order but less than that of the next higher order. Horton stated that "each of the successive orders of a basin approximate a direct geometric sequence" (Horton, 1945) and if the law of stream lengths is valid a plot of the logarithm of stream lengths as a function of order should yield a set of points lying essentially along a straight line (Figure 14). Linear regression lines have been obtained for all of the stream orders (Figure 14). The main drainage suggests good data correlation but an inspection of the data (Appen dix II, Table 14) reveals discrepancies seen on Figure 14. Fifth-order stream length drainage of both Pigeon Pass and Sycamore Canyons is extremely short for these basins pro ducing a large variance (16 per cent) for this data set. This may reflect reactivation of the drainage as headward erosion of first-order streams occurs. Mockingbirds' fourth-order drainage is also out of phase with the rest of the drainage suggesting that it was at this stage that the basin ceased to adjust to regional drainage changes. Divergence of the overall error lines is largest at the 5th and 6th orders (Figure 14) and suggests that despite differences in overall size of these basins, the same pro cesses are occurring in the heads of these streams. Varia tions for each drainage basin occur as the lower drainage 107 FIGURE 14. Graphic presentation of mean stream length. 108 LAW OF MEAN STREAM LENGTHS SOUTH FACE NORTH FACE SYCAMORE/ TEQUESQUITO • PIGEON PASS X o 2: LU _J 2 < LU cr CO 2: < LU 2 MAIN DRAINAGE MOCKINGBIRD BASINS ORDER 10 9 adjusts to regional changes in base level. Small drainage basins indicate a wide scatter of stream length ratios. South-facing ratios are generally smaller than north-facing slope ratios. Half of the small basins have smaller fourth-order streams equally divided between north and south-facing slopes and from the limited data available for this study does not appear to apply preferentially to those closer to the drainage divide or further from the source region. Stream length will be strongly influenced by stream capture and instability caused by tectonic uplift. Varia tions shown by this data when compared with the similari ties of drainage density and bifurcation ratio may indicate that in areas of structural instability, stream length variation may be significant. Granite terrain is relatively common throughout the southwest as major intrusions occurred during the Jurassic- Cretaceous in regions which now vary both in climate and vegetation. Granite is an impermeable bedrock developing coarse granitic soils. Channel development is geared to maximum rather than minimum runoff and new drainage lines are persistent. Deep weathering is associated with granite landforms and may account for the rapid adjustment of streams to tectonic and climatic change. Slope orienta tion appears to be important in this study as it controls lio vegetation, soil moisture retention, and bedrock exposure. Aspects of this study could be used to compare other areas within the Peninsular Ranges and outside of this area in the Sierras, and Idaho Batholiths. Drainage analysis also indicates that the valleys cloest to a fault zone are constantly adjusting to attain equilibrium while those further away exhibit a natural time lag response to uplift. FLOODPLAIN MORPHOLOGY The floodplain responds to the dynamics of a complete system of processes that constitute a stream system and the adjustments such a system makes to variable flows and loads derived from its drainage bains. The floodplain plays a necessary role in maintaining the balance that a stream system makes to variables in water, solubles, solid load particles and vegetation. Wolman and Leopold (1957) suggest that the active floodplain is that area subject to inundation by the annual flood. The Mediterranean climate of the Los Angeles Basin is also one subject to ten to eleven year pluvial cycles superimposed on a broader thirty to thirty-five year cycle (Figure 4). Therefore definition should be extended to cover areas flooded over a ten year period. Channel Form The distinctive features of sandy braided channels in- Ill eluding a wide, shallow bed choked with sand bars, emergent bars, rapidly colonized by annual forbes, shifting channels and distinct lack of well-developed bends characterize the Santa Ana River between the Riverside Narrows and Hamner Bridge. Discussion with water board authorities (French, pers. comm.) indicates the thalweg moves spasmodically under flood conditions but much more slowly during low flow stages from May until November. During this stage bed forms become emergent and are extensively modified, dissected and reworked by shallow water dune bed forms. The river in this study is defined as the area between the 3' Terrace (T10) and includes large areas of sand ac cumulation termed sand flats (Cant and Walker, 1978) that may be exposed for several years. Main channels surveyed in the summer and late fall commonly have a depth between 18 inches (46 cm) and 24 inches (61 cm) and rarely exceed 36 inches (91 cm) . Shal-r low reaches measuring 6-10 inches (15-25 cm) deep are com mon along the margins of the main channel and in channels dissecting emergent bars. Main channel width ranges from 170 feet (52 m) to 200 feet (61 m) but at most localities there are minor channels and islands which increase the total width to between 300 feet (91 m) and 370 feet (112 m) (Figure 15). The channel sinuoisty for the river is 1.1 (Leopold and ii'2 FIGURE 15. Diagram of floodplain channels and cor relation with ripple form. SAND FLAT ACTIVE CHANNEL RECENT EMERGENT BARS AND SHALLOW POOLS So Po Ar Ar RECENT EMERGENT MINOR BARS 8 SHALLOWS CHANNEL ISLAND a EMERGENT BARS TERRACE (TIO) Bedforms < x > Ripples T —r Dry Areas Large Dunes X= 1-2 m 3 0 ft. Planar Beds o m Small Dunes Xs .6-1.0 Vertical Exaggerated 113 114 Wolman, 1957) and the width/depth ratio averages between 115 and 140. The bed of the deeper channels are covered by rhomboid dunes varying in wavelength between 30 inches (76 cm) and 59 inches (150 cm). The crests of these dunes were in water depths varying between 8 inches (20 cm) and 20 inches (51 cm). The lee side scour pit averaged 8 inches (20 cm) in depth from the top of the arcuate dune face. These dunes were formed on long, low linguoid bars varying be tween 100, feet (30 m) and 62 feet (19 m) in length (Allen and Collinson, 1974) (Figure 15). Shallow channels ranging in depth between 3 to 6 inches (8 cm and 15 cm) had either planar, beds, or trans verse asymetric ripples with ripple lengths of 2.6 to 8 inches (7 cm to 20 cm) and heights of 2 to 3 inches (5 to 8 cm). These channels are subject to rapid changes in flow as water level decreases throughout the summer. These shallow channels and also the minor channels, may be rapidly elevated and abandoned. For a short period ripples and dunes can be seen on their surface but as drying and dessication continues, vegetation and wind modifies these surfaces. Channel erosion can be equally as impressive. In the mid 1970's during floodplain excavation near Riverside, an aluminum beer can was found 18 feet (5.5m) below the sur ii5 face (D. Trent, pers. comm.). This can was probably buried during the 1969 floods which occurred following two months of heavy rain totally 30.17 inches (76.6 cm) in 1969 (R.S.A.B.G. data). Intense rain over a short period of time results in rapid flow changes and abrupt changes in discharge (Figure 5). During this period the river is underloaded with suspended sediment and is able to erode deep channels. Subsequent rapid decrease in flow results in lower capacity and competence to carry material and deposition occurs. Bars The linguoid bars, that are submerged, are covered by dunes and ripples and this occurrence supports the proposal that they are large-scale bedforms generated during flood stage (Miall, 1977; Collinson, 1970). Bars are found where there is flow expansion as at Pedly Road (Figure 16) where a very minor tributary periodically 'dumps' sediment into the river, and also upstream above man-made obstacles such as bridges and flumes. This association of flow widening and bar formation was noted by Cant and Walter (1977). Single emergent bars range in length from 105 feet (32 m) to 310 feet (93 m), and from 13 to 36 feed wide (4 to 11 m). Small depressions on their surface become 116 FIGURE 16. Diagramatic sketch of bars and flood- plain morphology. 117 SANTA ANA RIVER FLOODPLAIN ENVIRONMENTS OLD DUNE AREA - — VALLEY SIDE SAND FLAT 0 CLOSE GROV AREA OPEN GROVE A C - MC - I " T - Active Channel Minor Channel Islands 8 Emergent Bars T erraces 118 the growth point for algal mats and those which emerge early in the summer may have a complex floristic sequence (see Plant Community section). Bar length which exceeds 225 feet (69 m) such as at Pedley Road represent composite coalesced forms. The older more central bars are stabilized by Arundo donax . anc^ Salix ssp. and form a vegetated nucleus for the expan sion of these islands. The bars range in height from . 4 to 18 inches (10 to 46 cm). During the falling stage following the high water level of 1980, the bars at Pedley Road coalesced in the minor channel which in 1980 was 70 feet wide (21 m). By fall 1981 this channel had been aban doned. The position of the deep channel against the margin of the T10 surface (Figure 16) was just discernible and was still barren of vegetation in November 1981. Just prior to emergence, the bars at Pedley Road were dissected around their margins by shallow channels 3 to 5 inches (8 to 13 cm) deep. This minor regular topography and depressions between dunes which had not been infilled provided moist areas where green algae and grasses rapidly became established. Areas which emerged late in the summer remained bare of vegetation due to high temperatures and were subject to wind deflation. 119 SAND -FLATS These form in areas of low fluvial energy and are analogous to the point bar deposits of meandering rivers. They range in width from 30 to 300 feet (9 to 91 m), and in length from 165 to 2290 feet (50 to 700 m). They are flooded approximately every two years (e.g., 1980) but emerge rapidly. Evidence of a minor channel may be found adjacent to the lower floodplain terraces and may act as a local conduit for flood terrace runoff and excess water from the main channel. Where more than one sand flat is separated from another by these minor channels they are termed sand flat complexes (Cant and Walker, 1977). Minor topographic features on these flats are bars of various heights, ripples and shallow depressions. They are rapidly invaded by annual forbes and later Salix spp., Populus fremontii and Arundo donax. As the water table de creases and the sediment dries out, these areas are sub ject to wind deflation, and sand sheet formation and low vegetation dunes develop. A sand flat developed during summer 1981 at Pedley Road as a result of channel abandonment and bar coalescence as a response to waning flow. Bars developed in the mouth of the channel which later became emergent blocking this channel. This sand flat is also increasing by lateral growth around the vegetative islands which formally separ 120 ated this area from the main channel. Smaller sand flats may also develop by minor channel erosion of larger sand flats. The sand flat at Pedley Road has been established by backfilling and coalescing of bars in a former erosional channel. At Hamner Bridge, a sand flat has also been created by man who is attempting to control major cliff erosion by diverting the Santa Ana into a new channel. East of Jurupa Railway Bridge these sand flat areas are mapped as River Wash on soil maps (Soil Survey, 1971) and correspond to those areas where there is rarely year- round flow and vegetation is sparse. West of this bridge they are mapped as soils of the Dello Series, which are Typic Psammaquents. Year-round flow provides sufficient moisture to establish dense growth of Arundo donax, Salix sp., Populus sp., and annual forbes (Appendix I, Table 12) which add sufficient humus to allow development of an A soil horizon. These soils are saturated with water part of the time, but the sand fraction is well sorted and re worked by wind. This environment would be created by the shifting sand flats as already described along the Santa Ana River. SEDIMENTARY CHARACTERISTICS Sediments found on the Santa Ana floodplain are de rived from two distinct geologic provinces, the San Gabriel 12 i igneous/metamorphic complex and the granitic terrain form ing the Perris Block. The sediment from this latter ter rain is poorly sorted; coarse sand with a distinctive grain size bimodal distribution characterized by a lack of sedi ment in the very coarse sand fraction (-1 to 0 phi unit size) (Figure 7). Tributary streams from the San Gabriels are longer than those from the Perris block and both channel and bank sediments are finer and better sorted (Figure 17). Bank deposits are slightly finer than modern stream deposits. Clay mineralogy (McMurty and Fan, 1975) shows that montmor- illanite and kaolinite derived from the weathering of grus in the tributary watersheds draining this section of the Santa Ana basin increase at the expense of chorite and amphibores. These minerals are present only in small amounts and are masked by the large addition of montmoril- lonite and kaolinite. This material probably formed largely from weathering of feldspar and non-micaceous fer- romagnesium minerals found in the metamorphic and igneous rocks in the drainage basin of tributary streams, Floodplain Sediments Floodplain sediments were collected from three tran sects of the Santa Ana River at Mt. Vernon Ave., Jurupa Railway Bridge and Pedley Road (Figure 6). Samples were 122 FIGURE 17. Analysis of sediment samples from the San Gabriel Mountains. 123 DRAINAGE FROM SAN GABRIELS ACTIVE CHANNEL BANK DEPOSIT LYTLE CREEK LCG m = 1.34 SD»I.46 Sk=1.60 K*5.25 LCE m = 0.92 SD= 1.67 Sks T l6 L KS3’ 28 LCF m = 1.75 SD = 0.77 Sk= 0.94 K= 11.57 ■ =k -2 0 2 4 MIRA LOMA CHANNEL □ 20- r-| - ML 37 - m s 2.57 - SDs 0.61 _ Sk- 0.23 - “1 K*5.59 fC 1 n ML 38 m = 2.90 SD=_0.97 Sk= 0.56 K= 6.29 -2 0 2 4 DAY CANYON WASH S 4 6 m=2.l7 SDs 0.73 Sk= 0.16 CL K * 3 ' 2 2 S 47 ms 2.68 SD* 0.94 Sk=T.2l Ks 11.85 tn -2 0 2 4 GRAIN SIZE IN PHI UNITS 124 collected from the active channel, adjacent shallow chan nels, adjacent sand flats, three-foot terrace (T10) and eight-foot terrace (T9), Comparisons of sediment within the active channel and adjacent shallow channels shows both a progressive decrease of sediment grain size and better sorting downstream. In all cases the shallow channel is slightly coarser than the active channel (Figure 18). These sediments represent a lag deposit as channel depth decreases and the current is unable to carry all material as a bottom traction load. Sediment on the sand flats is finer than in the chan nels ranging in mean grain size from .174 mm to .275 mm. The material is moderately well-sorted to very well-sorted and represents many diverse micro-environments. Reworked sediment further from the river where sediment dries out rapidly and vegetation growth quickly dies is reworked by wind and forms rippled sand sheets and small dunes. Sam ples from these environments are illustrated by samples 3, 28, and 42 (Figure 18). Areas which have not undergone wind modification are slightly coarser and moderately well- sorted and represent finer overbank deposits. Frequently these areas are also covered with a more dense vegetation of annual forbes and young saplings of Salix ssp. and Populus fremontii which trap a more variable sand size range. 125 FIGURE 18. Santa Ana River floodplain depositional environments. WEIGHT % DEPOSITIONAL ENVIRONMENTS TERRACE (T 9 ) 6 0 4 0 20 0- 60- 4 0 - 20- 0 JT 4 4 m=3.03 SD=0.80 Sk=0.09 K=3.44 PeT 29. m=2.28 SD=0.74 L Sk=0.48 K=3.I8 0 2 4 TERRACE (T 10) SAND FLAT 8 DUNE FIELD J JT 4 3 m=2.88 SD=LI2 Sk=0.55 K=5.3I d PeT 3 4 m= 2.54 SD=0.49 Sk=0.97 K=7.44 2 4 60 4 0 - 20- 0- WD tt, m= 2.41 SD=0.70 Sk=0.66 K=3.79 Pe 28 m=2.52 SD=0.35 Sk=0.63 K=9.95 da. 2 4 V 4 m=l.86 SD=0.56 Sk=l.24 K=4.29 \L dcu Pe 2 7 m=2.47 SD=0.62 Sk=0.35 K=3.74 ri Pe 2 6 ACTIVE CHANNEL SHALLOW CHANNEL V 3 m=l.50 SD=0.56 Sk=l.66 K= 10.2 J 42 m=2.50 SD=0.52 Sk=0.89 K=7.02 tL a . m=2.34 SD=0.74 Sk=0.46 K= 3.7 6 2 4 0 2 4 GRAIN SIZE IN PHI UNITS R-C m=l.57 SD=0.9I Sk=2.02 K=I2.I V 2 m=l.28 SD=L42 Sk= 1.61 K=5.23 a -R J 39 m=2.03 SD=0.79 Sk=2.l8 K=I3.5 R-T J 4 0 m=l.9l SD=0.99 Sk=2.36 K=ll.5 h -T Pe 23 m=l .79 SD=0.87 Sk=2.34 K=I3.4 -2 0 R 2 4 Pe 2 4 m=2.02 SD=0.74 Sk=2.56 K=I6.9 R-fH -2 0 2 4 ML Vernon Bridge Jurupa Railway Bridge Pedley Road fo CPi 127 The three-foot and eight-foot terraces have been elim inated at Mt. Vernon Avenue by recent flood control channel modifications. Both of these terraces are also extremely narrow at Jurupa Railway Bridge which is located at the narrowest point of the Riverside Narrows. This area is subject to rapid channel modification during floods and the terrace deposits, although finer than the sediment in the active channel, reflect variable conditions. At Pedley Road, sediment from the three-foot terrace (T10) indicates that prior to intense vegetation growth, wind sorting was an important modifier of fluvially derived sediment (Figure 18) . Sediment was also collected from the Wisconsin dune sheets which developed on the Wisconsin Terrace T7. A typical grain size distribution (Sample D) has a mean grain size of .188 mm, but is only moderately well-sorted. These fluvially derived sediments are slightly weathered which may account... for. their grain size distribution. ENVIRONMENTAL FACTORS Within the study area sediment can be collected from primary source areas. This can be compared with sediment which has undergone transportation, erosion, deposition and mixing of several populations in a fluvial system. Old fluvial terraces have also undergone some slight cementa 128 tion and weathering. Tributaries to the Santa Ana River are all ephemeral streams so that their capacity and com petence for sediment movement is controlled by seasonal change. Within the floodplain, sediment deposited on the sand flats is also subject to wind erosion as the areas 'dry out1 during the long hot summer associated with Medi terranean climate and later Santa Ana wind conditions. Samples from all these environments are displayed on a diagram of moment standard eviation (sorting) plotted against moment skewness (Figure 9). Granite grus is bi- modal but sediment from this source becomes modified by transportation. The coarsest grains are deposited close to the source but with increasing distance the removal of this material results in a better sorted and more negative distribution. No weathered material from the San Gabriel Mountains was analyzed but sediment from this region lies within the granite grus transportation population. Older alluvium from the granite grus can also be isolated as a distinct population and may reflect chemical weathering in situ modifying sediment distribution. Permanent flow in the active channel of the Santa Ana River and the distinctive population from this group re flects the capacity of the river to transport bedload. These fluvial sediments are strongly modified by wind when exposed on the sand flats. The Wisconsin T7 deposits 129 can also be included in this group. Intermediate between these two extremes are a group of sediments collected from the higher terraces of the Santa Ana River at Jurupa Bridge where flood conditions may fluctuate rapidly. An abandoned bar at Pedley Road, and deposits from channel banks along tributaries originating from the San Gabriels characterize these conditions. These sediments may represent a population of fluvial sediments which are rapidly deposited as flood level subsides. Dis charge from the Santa Ana River and its tributaries can fall abruptly (Figure 5) leaving bed forms stranded. These will contrast from those in the active channel which can adjust to changes in discharge and reflect the steady state condition of the river. Rapid spring growth of vege tation would further protect these sediments compared with those on other areas of the sand flats which are exposed to wind deflation. The Rialto Bench is an anomaly. These sediments are Sangamon in age and may represent sand flat sediments which have been deeply weathered. Discharge rates on the Santa Ana River fluctuate from year to year and reflect the periodicity of the Mediter ranean climate and yearly rainfall variations (Figure 5). In an extremely wet year such as 1979-80, hydrograph varia tions indicate a period of intense scour, deposition and 130 stranding of bed forms as indicated by Jones (1977). Under these conditions major shifts in stream channels occur and surfaces are abandoned. Under more normal conditions, during the spring, small bedforms are superimposed on bar structures. These are emergent during the late Summer and Fall if the overall rainfall has been low as in 1981 causing dissection of the sand bars and the development of sand flats where the channel widens and small, minor tributaries enter the Santa Ana River. VEGETATION PATTERNS Erosional deposits left on floodplains and changes in stream courses can be a major factor in the various stages of plant succession towards a climax community. River terrace communities begin anew with the formation of each bar and island along the river bed, but it is their fate to be undercut and washed away. Daubenmire (1968) used the development of vegetation on varying terrace levels to differentiate various ages of terraces. The colonization and growth patterns of annuals and perennials could be used to differentiate both recent floodplains and older terrace sequences. Prominent plant communities can also be changed as man removes components of the original biota and introduces new plants which survive better in man-modi fied environments. Such species found along the Santa Ana 131 include Arundo donax (giant reed), introduced from Asia and first collected along the Los Angeles River in 1889, Meliotus alba (sweet clover), first collected in 1890, and Tamarix gallica. The original vegetation was described as alders, cottonwoods, willows, and sycamores up to four feet in diamter. During this study period no sycamores were found and many cottonwoods were either dead or dying. Vegetation growth patterns reveal a mosaic development along the floodplain which is summarized in Figure 18. Active Floodplain and Sandflats This first level is defined by Hefley (1937) as that area comprising the river bed and adjacent sand bars. The area of active river bed is small and fluctuates in size dramatically as a function of rainfall and runoff. In October 1980 the active flood channel at Pedley Road (Fig ure 8, location 3) was a double channel 198 feet (60 m) wide separated by a small island but a year later the channel was reduced to a single meander loop 171.8 feet (42.3 m) wide and the former channel was dry and contained Typha latifolia, Meliolutus alba, seedlings of Salix spp., Populus fremontii and Juncus spp. This former channel has infilled by deposition within the channel. Reduced flow resulted in emergence of the original channel point bars and planation at bedforms. The initial plant community 132 observed along the margins of the channel as former chan nels emerged was always composed of blue-green algae. Fol lowing the algae species of Juncus, Typha latifolia, other perennial and annual grasses appear during the pre- vernal period, to be followed by Salix ssp., Populus fremontii, Nasturtium officinale (watercress), Veronica- anagallis aquatica (speedwell) and Bidens laevis (Bur- marigold) during the vernal period. An important perennial grass with strong root binding properties which grows as water level subsides is Distichlis spicata var. stricata. This low floodplain is composed of coalescent bars deposited originally within the stream channel. Heavy floods can destroy all this vegetation but many seedlings survive winter floods by being flattened by the water rather than being washed away. Populus fremontii, Arundo donax, some Salix sp. and Distichlis spicata survive by sending up new shoots which form the base for sand deposi tion which begins the build-up to level II. 4 Many annual forbes also invade this area as water level recedes but they are subject to die back during the summer drought. This is especially true away from the river where water supply becomes critical. In this region thin, wind-sorted sand sheets develop which may also form small shadow dunes around young saplings of Salix. sp. and Populus fremontii. This area away from the main channel 133. and the shifting point bar deposits constitutes the over- bank deposits but under high water conditions all the vege tation from this zone can be washed away and a thin veneer of finer overbank material deposited. Terrace TIP This first terrace is an abandoned floodplain at 3 to 5 feet (0.91 m to 1.5 m) above the present floodplain and is subject to erosion as the Santa Ana River migrates laterally and reverses its course across the floodplain. A subdued topography on this surface represents distinct relicts of former channels. Where least disturbed near Hamner Bridge, a channel is found at the margin of this floodplain terrace which is a drainage channel maintained by overbank flow when this area is flooded under maximum flood conditions which occur once in approximately 30 years. The edge of this feature is often marked by dense stands of almost impenetrable Arundo donax. Within this terrace there are stands of different ages of vegetational growth adjacent to each other reflecting shifts of meander loops across the floodplain. Initial communities found on the wetter lower por tions are composed of Salix spp., Populus fremontii, Arundo donax and Baccharis viminea. In these areas, 134 Populus fremontii are rarely more than 4 feet tall (1.2 m) but willow such as Salix hindsianna are quite large pro viding protection and shade for the Populus. These trees also send up shoots from outlying roots which also pro vides anchorage for sediment while soil litter begins to build up to provide soil nutrients. Median age groves at Pedley Road (Location 3) are 40 to 60 feet (12 to 18 m) high and range in age between 4 0 to 65 years old (Andrews, 1972 and pers. comm.). These trees form closed dense groves beneath which grow scattered Salix (willow) , S3, lasiolepsis and S3, hindsiana, varying in age between 3 to 15 years. Sambucus mexicana (Elder berry) may also be found in these groves and on the margin Nicotiana blauca (Indian tobacco). Vitis girdiana (wild grape) is commonly found climbing all of these trees. On slightly higher ground, are distinct, more open groves of Populus fremontii. Increment bores indicate these trees growing in distinct, separate pockets, range in age from 75 to 180 years old (Andrews, pers. comm.). Many are declined or dead and infested with mistletoe. Salix ssp. are found only around their margins or in depressions which may periodically collect water. Soils beneath these groves are higher in humus than on the floodplain as they are higher and older than the soils on the present flood- plain and less disturbed by recent deposition. The soils 135 on this level are mapped in the Dello Series, which are Typic Psammaquents. Between the youngest Salix - Arundo - Populus stand adjacent to the river and the older groves as previously described there is an area of dune fields where the flood- plain widens west of Van Buren Avenue and continuing to Hamner Bridge. These dunes are 2 to 3 feet (0.6 to 0.92 m) high and occupy a similar location as the sand sheets on Level I except they are larger. Grasses, especially Bromus sp. and Distichlis spicata provide a light cover and in early spring Erodium cicu- .... tarium (filaree). Later this area is invaded by Salsola kali (Russian thistle). Sand movement is important in the fall when these weedy species die and the few Salix spp. in this area become important dune vegetation builders. Terrace T9 This terrace stands 6 to 9 feet above the floodplain. It is subject to disturbance including housing, light in dustry and west of Van Buren Avenue (Figure 4, back pocket) is used for crop and dairy farming. Unlike the lower level the vegetation is not riparian but more typical of dis turbed coastal sage scrub and associated weedy species. Depending upon the degree of disturbance a progressive sequence from grasses and weeds such as Bromus spp., 136 Distichlis spicata, Erodium cicutarium (filaree), Salsola kali (Russian thistle) and Marrubium vulgare (Horehound) are abundant where disturbance occurs. Artemisia californica (sage brush), Croton californicus, Eriogonum fasciculatum (wild buckwheat), Senecio douglasii (brittle bush), Sambucus mexicana (Elderberry) and Nicotiana glauca (Indian tobacco) appear later if the area is undistubed. Artemisia californica and Croton californicus can also be found on the dune areas where xeric conditions exist. This terrace is a true floodplain terrace west of the Riverside Narrows but cannot be differentiated from alluvial fan de posits along minor stream terraces onto the floodplain east of Riverside. Tributary Streams Along tributary streams the dominant vegetation is Salix spp., Sambucus mexicana, Nicotiana glauca and Baccharis vimnae (mule fat). As on the main floodplain no sycamores or alder were found and only one stand of Populus fremontii was found in Mockingbird Canyon. This emphasizes the xeric climatic conditions and that many streams are ephemeral. DISCUSSION Early descriptions of the Santa Ana River describe a lush, tree-lined water course carrying water throughout 13.7 much of the year. Removal of alder and sycamore for lumber and firewood and the creation of farmland has resulted in denudation and the development of a more restricted ripar ian vegetation. Water tables have been drastically lowered and natural runoff is manipulated both by dams, man-made channels, and rapid street runoff following storms. The present floodplain reflects man's attempts to control potential flood hazards by bulldozing new channels, in addition to the effects of yearly fluctuations in rain fall. 1980 was an exceptionally wet year resulting in a broadened floodplain and some cliff erosion, but 1981 re sulted in drastic reduction in flow. The exposed flood- plain was rapidly colonized and sand sheets formed in areas where the floodplain dried out rapidly. Increment bores of Populus fremontii and Salix spp. on Terrace T10, show that there are localized areas of vegetation growth which vary by as much as 100 years and reflect different vegetational zones. These zones all appear to be on the same level but may be related to both growth habits and recent floods along the Santa Ana River. Within Terrace T10 there are at least five vegetation zones: (1) Salix - Populus - Ty.pha community adjacent to the river bank and on small islands where Typha overtops all other species; (h) Salix - Populus - Arundo community, a dense river margin dominated by Salix and Arundo sap-.. 138 lings; (c) dune communities associated with annual grasses, and forbes, and Salix hindsii; (d) closed Populus groves with ages between 45 and 60 years; and open declining groves of Populus with ages between 100 and 120 years. Populus fremontii is the species with the longest life span yet it appears to require shade during the seed ling and sapling stage to reach full maturity. This is provided by Typha and later Salix spp. which have a rapid growth rate. The tenacious root systems of Arundo donax and Salix sp. provide bank stability capable of with standing all but the most severe floods. Eventually Populus fremontii exceeds Salix sp. in height which grad ually die because of lack of light. Salix also declines in vigor after about 18 years (Andrews, 1972). Dying Salix and shade tolerant plants develop into almost in- penetrable closed groves. Populus in these groves range between 40 to 65 years, although in adjacent open groves on the same terrace they range from 75 to 180 years. The dune area is located between the riverine groves and the more mature Populus groves. This is an area sub ject to washouts when floods spread into this terrace. It is also located in a similar location to the sheet sands on the floodplain and is an area where species of Salix and Arundo donax requiring much water cannot exist and Populus seedlings do not become established because they require 139 water during germination. Sand is shifted by strong Santa Ana Winds and plants are adapted to xeric conditions. Salix hindsiana, prolific in the dune areas is more drought tolerant than other willows, and its root sprouting habit provides stability for these dunes. On the Candian River, Hefly (1937) proposed that higher terrace levels build up as a result of water and wind action. Along the Santa Ana River this second ter race, T9, represents remnants of small alluvial cones de posited by streams during the Holocene. The 1862 flood was a major even in the history of the San Bernardino Valley. This flood scoured out a new chan nel for the Santa Ana River besides removing vegetation. This flood was followed by a drought cycle which caused the demise of many large cattle ranches. Already many alders and sycamores had been removed and these are all trees requiring large amounts of near surface water. No Populus fremontii pre-date this event and it is suggested that Terrace T10 developed at this time. Mature groves of Populus fremontii have been designated dense closed groves which are 40 to 65 years old and in the open grove 75 to 180 years old. Many of these older trees are declining. The average life span of a Populus fremontii has been esti mated at approximately 150 years. This suggests that the first terrace, T10, has been a stable feature for at least 140 the last 150 years. Many trees with bore increments of 120 years old suggest that episodic floods are of major importance in floodplain vegetation growth. The mosaic of growth patterns also reflects shifts in meander loops and subsequent invasion by plants. Open dune fields re flect the interplay of Mediterranean xeric climate and critical periods of vegetation establishment. They are not protected by the growth of Populus fremontii and the sand shifts under strong wind conditions. The present floodplain is 3 to 4 feet (0.9-1.24 m) below this older terrace suggesting degradation has oc- . . . curred in the last 15 to 20 years. This may be accounted for by increased floodplain management, decreasing water supplies, and urbanization. This floodplain is one of active erosion today and erosion of Terrace 10 occurred during the 1980 floods. EOLIAN DEPOSITS A small part of the study area is covered by an area known locally as the "Sand Hills." This major dune area lies north of the Santa Ana River and west of Lytle Creek. The total area of this dune field exceeds 6.9 square miles (18 square km) and extends about 2.5 miles (4 km) in an east-west direction and more than 3.1 miles (5 km) from north to south. These deposits have accumulated on the T7 141 terrace of the Santa Ana River (Figure 19, back pocket). Santa Ana Wind conditions develop as high pressure builds up in the Mojave Desert and central Nevada during the fall, winter and spring and air currents are funneled through Cajon and Banning Pass into the San Bernardino Valley. As these northerly and northeasterly winds flow into the valley they are heated by descent and compression. The La Loma Hills, a series of inselbergs slightly over 1400 feet (434 m), are sufficient in height and size to produce eddies in the lower air flow current. The sediment source for these dunal deposits are dis tal, alluvial fan deposits and active stream channel de posits of the extensive Lytle Creek and Santa Ana River. These stream channel sands are relatively coarse and mod erately sorted. As the sand flats emerge and channel width decreases, these sands are subject to wind defla tion as the water table deepens during the summer drought. This wind modified material is better sorted, finer grained and can be built into extensive dune fields (Figure 18). Sand Hills dune sediment is composed of coarse to very fine sand particles which form active sand sheets and small vegetation dunes, and large fixed dunes. Grain size ranges between 2 mm to less than 0.061 mm with a mean diameter of 0.188 mm. These dunes are moderately well 142 sorted to well sorted with a range between .480 mm and .700 mm depending upon whether they are from active sand sheets or moderately cemented old dune fields. These sorting parameters are similar to those from the sand flats and the three foot riverine terrace deposits which have been subject to wind modification. They are finer and better sorted than fluvial channel sediments (Figure 18). Hand lens examination indicates that they.are approxi mately the same composition as the Santa Ana River deposits being composed of quartz, feldspar, small rock fragments, mica, biotite and hornblende. MORPHOLOGIC FEATURES This area has been the subject of extensive research by Anthony Clarke (1980) and fieldwork verifies his con clusions. Three periods of dune development are recognized in the area and each period is associated with different morphologic form or modification of former major features. Longitudinal Dunes These dunes are the oldest and largest dunes in the Sand Hills complex and are best seen north of the San Bernardino Freeway. They trend north to south and are approximately 327 feet (100 m) wide, 39 feet (12 m) high and the largest is 1.2 miles (2 km) long. They are ap proximately 545 yards (500 m) apart. These dunes form an 143 area of gently rolling topography as they have been wea thered and modified by erosion. These consolidated dunes are thin bedded and recent sand erosion may etch out this lighly cemented laminar bedded dune sand. No evidence of cross bedding and large scale migration was found. South of the Freeway, the topography is more complex. Longitudinal dunes are smaller measuring 980 feet (300 m) long and rising to a height of 25 feet (8 m). These dunes are further from the sand source. Sand Plain On the western margin, a thin veneer of eolian ma terial overlies alluvium. Dune sediment is structureless and appears to represent an area of old sand sheets. In sufficient sediment was available for dune formation or complex eddies may have developed around the end of the Jurupa .Mountains. Blowout Depressions and Parabolic Dunes Blowout depressions occur to the south of the San Bernardino Freeway. Some are relict features and are stabilized by vegetation, others are filled with loose sand and may represent recent disturbance (possibly since 1860's). These blowouts are associated with small para bolic dunes although more complex, and are associated with formation by both northerly and westerly winds. These 144 dunes are stabilized today unless disturbed for building and off-road vehicles. This section of the dune field is more complex than the mega-longitudinal ridges to the north and represents an area of decreased sediment supply. The complex microtopography has made it a popular off-road vehicle area which further destroys the dune form. Coppice Dunes Small dunes ranging in size from three yards to sev eral tens of yards in length (3 meters to several 10's of meters) have formed around clumps of vegetation including Nicotiana glauca (Indian tobacco), Salvia apiana (white sage) and Artemisia California (sagebrush). They are most common south of the Union Pacific Railway where off-road vehicles, lee eddies from Colton Hill and La Loma Hills and westerly winds sweeping up the Santa Ana Valley inter fere with the dominant but still periodic northerly winds. Some dune forms are simple shadow dunes in the lee of the vegetation, others are more complex. Throughout this area are superimposed minor sand ripples. These small asymetric transverse sand ripples have an average wave length of 4 to 10 inches (10 to 25 cm) and an amplitude varying between 1 and 3 inches (2.5 to 7.5 cm). They may be superimposed on dune surfaces, and sheets and blowouts. 145 Dune Soils The fine grained quartz-rich sandy parent material does not allow the development of mature soil profiles. Natural edaphic conditions, high permeability and shifting sand results in only limited vegetation growth and contri bution of humus to the A horizon. Soils of the Delhi Series, Xeropsamments, develop on this granitic material that has been reworked by wind. The surface layer is typically a light brownish-gray (10YR 5/2). fine sand overlying dune bedded fine sandy unaltered or lightly cemented parent material (Appendix III, L; Figure 20). Along a recent stream cut a massive longitudinal dune overlies a buried Ocrept soil developed on Wisconsin gravels (Figure 20). No carbonates are associated with this soil but a wood sample was radiocarbon dated from the same homotaxial surface preserved to the east in Lytle Creek wash at 33,000 ±900 years B.P. (Elder et al., 1973). The preservation of this soil suggests a sufficient period of time elapsed before dune development for an Ocrept to develop on coarse fluvial material. Birkeland (1974) suggests that at least 5000 to 10,000 years would be required to develop such a soil on coarse fluvial sands and gravels (Appendix III, L). 146 FIGURE 20. Vertical description of Wisconsin dune succession and underlying Riverside Surface. 147 lll» . 0.0 v ° A 0.0a < \ [ '?o?& 1 -oo O <2’ o'o 7 7 7 " Al A BI B 2 C Gu&**besi 12.6 m (42 ft) Recent 5n Psamments Cross bedded Wisconsin dune sands Total thickness 7.02 m (23ft.) ft o. -i 0 m Fossil Soil KEY Massive fluvial cobbles 8 gravels grade into coarse sands Tabular planar bedded thin fining upward gravel units Layer of carbon coated cobbles LLLLl y y yy / / / / GRAIN SIZE ,gravel 8 cobbles sand silt 8 clay LITHOLOGY silty- sand sand conglomerate STRUCTURES dune cross bedding planar bedding BASAL CONTACT transitional abrupt erosional SAND HILLS SECTION COLTON, CA. 148' Dune Field History Clarke (1980) , divides the various dune forms into three series. The oldest, Series III, includes the large longitudinal dunes, fossil dune plains or sand sheets. These dunes overlie the Lytle Creek surface dated at 33,000 years ± 900 years B.P. and probably developed prior to the last Wisconsin glacial, Tioga stage in California. The initial onset of pluvial conditions would result in erosion and stripping of the San Gabriel, San Bernardino Mountain as streams removed detrius accumulated on the hillslopes during the drier interglacial conditions. Dune alignment can be attributed to strong, persistent winds of constant direction blowing through Cajon Pass at this time. Large quantities of detritus on the flood- plains of Lytle Creek and the Santa Ana River floodplain would be available for dune formation. The Santa Ana River checked their southerly movement. Entrenching of this Lytle Creek surface was caused by uplift along the San Jacinto fault. Stream piracy and reduction in sediment supply towards the end of the Pleistocene terminated this phase of mega dune buildup. Series II dune phase is characterized by dune blow outs. Recent research in Arizona indicates a warmer, dryer arid climate existed in the southwest known as the Xerothermic from 8000 to 5000 years B.P. (Van Devender, 149 1977). The older dune field was the source of sediment for the smaller parabolic dunes and blowouts would be fre quent as dessication continued without vegetation holding these dunes. This period ended when cooling associated with the Recess Peak Stage, around 3,000 years B.P. increased rain fall and dune field stabilization by vegetation. Droughts in the 1860's, increased human activity and present day off road vehicular use has resulted in the final Series III development of sand sheets, complex coppice dunes and blowouts. This three phase development reflects similar patterns described in the Sand Hills of Nebraska (Smith, 1965) and the Southwest (Melton, 1940). ALLUVIAL FAN DEPOSITS Recent alluvial fan outwash deposits have been built up by streams draining the San Gabriel Mountains. They extend south to the northern front of the Jurupa Mountains, a distance of 12 to 15 miles (10 to 24 km), and then ex tend around the western and eastern margin of this range. The toes of these coalescing fans form a gently inclined plain indicated on Figure 19 by the symbol QF on the land- form map. Along the western margin of the Jurupa Mountains a rolling ridge and swale topography associated with NE-SW aligned ridges indicated as QFI on Figure 19 indicates 1;5 0 recent reworking of these deposits. Storm runoff from the San Gabriels is now controlled by a series of major flood control channels and settling basins maintained by the various flood control agencies. Eckis (1928) records that flood water under extreme condi tions could reach the Santa Ana River, 20 miles (32 km) from the dissected fan apexes. In 1969, parts of Mira Loma were flooded by excess runoff along these swales after two Pacific storms had resulted in a record rainfall of 16.69 inches (42.4 cm) for the month of January (rain fall data Rancho Santa Ana Botanic Garden). Shallow trenches inspected in new housing developments indicates that this plain is composed of horizontal planar beds of alternating coarse sediment grading upwards into finer deposits. The beds vary in thickness between 1.5 and 4 inches (3.8 and 10 cm) and are similar in appearance to present day bank deposits along Lytle Creek and the abandoned surface adjacent to Lytle Creek which can be studied in gravel pits today. These deposits were laid down by overflow streams under high runoff conditions. Wind reworking of these deposits occurs during the summer drought. During the extreme arid conditions of the Xero- thermic Period this material became the source area for the large sand sheets which extend up into the valleys and bury an older fan surface on the northern margin of 151 the Jurupa Mountains today. These sand sheets are asso ciated with soils of the Delhi Series and can be observed along La Sierra Avenue, Fontana. These fan deposits overlap Ramona soils along Hamner Road and the western margin of the Jurupa Hills and appear to be continuous with the Pedley Surface. EROSION. SURFACES Ten erosion surfaces have been recognized in the area. Two are interpreted as bedrock erosion surfaces, two as alluvial surfaces, and six as fluvial floodplain terrace surfaces. These surfaces form a distinct chronosequence (Table 1). The two alluvial terraces are part of the re cent floodplain deposits of,the Santa Ana River but are included because they reflect changing hydrologic condi tions in the recent past. Local geographic names have been assigned to these surfaces (as recommended by Howard, 1959) for the purpose of correlation during this study. They are the Box Springs Canyon Surface (Tl), Jurupa Surface (T2), Canal Surface (T3), Limonite Avenue Surface (T4), Riverside Grand Terrace (T5, [Eckis, 1945]), Pedley Surface (T6), Lytle Creek Surface (T7), Mira Loma Terrace (T8), High Flood Plain Terrace (8-foot Terrace) (T9) and the Low Flood Plain Terrace (4-foot Terrace) (T10). The areal distribution of these surfaces are shown on Figure TABLE 1. Chronosequence of erosion surfaces and terraces of the northern Perris Block and Santa Ana River Basin between Riverside and Corona. Surface # Surface Name Surface Type Pedon Description # T1 Box Springs Canyon Surface Strath A,B,C T2 Jurupa Surface Strath D, E, F T3 Canal Surface Alluvial Fan G T4 Limonite Avenue Surface Alluvial Fan H T5 Riverside Grand Terrace Fill Terrace I T6 Pedley Surface Fill Terrace J,K 17 Lytle Creek Terrace Fill Terrace L,M IS Mira Loma Terrace Fill Terrace N T9 High Floodplain Terrace Floodplain 0 T10 Low FIoodplai n Floodplain The pedon descriptions are located in Appendix III. < _ n N J 153 19 ( b a c k p o c k e t). Box Springs Canyon Surface (Tl) This surface is developed on granite bedrock and is well preserved today at the head of Box Springs Canyon, Riverside. It forms a gently northward dipping surface below the crest of the Riverside Escarpment between 1300 and 1400 feet (400 and 434 m). In the area of Box Springs it is presently being dissected by small streams. Large areas form horizontal bare bedrock exposures indicating that it may have formed an extensive pediment surface which has since been stripped of its overburden. Ober- lander (1974) recognized that such surfaces are typical of areas that have undergone deep weathering and then re juvenation associated with climatic change and tectonism. This surface forms a major regional feature on the north- facing slopes of the Perris Block. It is associated with well developed soils of the Fallbrook Series (Appendix III, A). One locality was examined where a truncated B horizon Fallbrook soil was overlain by a well developed Typic Haploxeralf (Appendix III, B) indicating that there was a period of valley eluviation after this surface had de veloped. This surface does not extend to lower regional sur faces and represents a remnant erosional pediment. This 154 surface is also represented by extensive sloping surfaces in the La Loma Hills to the north of Arlington Gap. Many isolated flat-topped summits between 1350 feet (418 m) and 1400 feet (434 m) in the Jurupa Hills may also represent extensions of this former widespread terrace, a classic example being the flat-,topped summit of Mt. Rubidoux near Riverside. Along the western slope of La Sierra Canyon there is also an extensive remnant of this surface preserved as a shallow north-draining valley newly isolated from the main valley. Recent streams exploit this topographic low and create abrupt elbows of river capture and short stream lengths parallel to the main canyon trend. Observed from Arlington Mountain this surface looks like a small alpine alp. Jurupa Surface (T2) The Jurupa surface is distinguished by isolated rem nant surfaces between 1100-1200 feet (340-372 m) in the Jurupa Mountains and extensive bedrock surfaces along the eastern margin of the Riverside Escarpment. In the west-, ern section of the escaprment below Arlington Mountain this surface is represented by isolated coarse alluvial fan deposits which are perched above the Arlington Gap and lower surfaces. 1.55: In the Jurupa Hills, this surface is found in iso lated wind gaps and the surface is broken by numerous deep ravines. Morton (1978 and pers. comm.) has found clasts of Pelona Schist associated with well developed soils on this surface in two areas of the Jurpa Hills (sec. 4 T. 2 S., R. 5 W., and sec. 5, T. 2 S., R. 5 W.). Drainage across the Jurupa Hills was southwards. Fossil soils associated with this surface in the Sierra Avenue wind gap are ce mented and consist of massive B horizons overlying coarse rubbly C horizons (Appendix III, C). Pebbles in this hori zon when they can be removed from the cement matrix crumble easily in the hand and are extremely well weathered. East of Sierra Avenue this surface is preserved above Ormond Quarry and on the eastern side of this wind gap valley. Drainage was to the south and the present valley has formed along the west flank of this south-draining valley which is now preserved as an erosion surface. Soils on the sur rounding slopes are of the Vista and Cieneba series (Appendix III, C, E and F), but locally soils on this surface are well developed with argillic subsoil horizons which contain fragments of Pelona Schist. The color of the B horizon is reddish-brown (5 YR 4/4) when dry and this is characteristic of intensely weathered old soils. This area is dissected by narrow, deep gullies. Indications of recent headward erosion may reflect disturbance by off- 156 road vehicles, and increased runoff as urbanization extends into these hills. Below Arlington Mountain the T2 surface dips north wards and is associated with Cajalco fine sandy loam and Vista coarse sandy loam with 15 to 35 percent slopes. This area is preserved 200-300 feet (62-93 m) above the River side Grand Terrace Surface (T5) in this area. It is cur rently being dissected, but appears to have undergone at least two stages of dissection. The latest phase is the development of deep ravines characteristic of narrow fan- head trenches, but an earlier period developed a rolling topography on this alluvial fan surface. This surface is associated with many small valleys which once extended onto the fan surface. These are now all beheaded by recent fan- head entrenchment. These ravines terminate on the present Riverside Grand Terrace Surface (T5). Canal Surface (T3) This surface is persistent at higher elevations around the margin of the study area. On the south flank of the Jurupa Mountains it forms isolated bedrock platforms fre quently chosen for the location of water towers. On the margin of the Perris Block it can be found at the head of many alluvial fans and may either be associated with a pronounced increase in slope gradient (as in Pigeon 157 Pass) or a terrace and erosional escarpment as around the University of Riverside campus, Mockingbird and Sycamore Canyons. Frequently associated with these terrace deposits are Buren soils (Appendix III, G) which have a calcium car bonate horizon (B3 ) overlying a massive silica hardpan c a (Cls^, at depths varying between 36 and 52 inches (91 and 132 cm). Several hardpans occur at the head of Pigeon Pass representing a sequence of paleosols and fossil soils forming persistent ledges along the edge of the in cised fanhead trench. This surface is characterized by slopes varying between 2 to 15 percent. Dissection of this surface has occurred by streams which terminate either on the Riverside Grand Terrace such as Mockingbird Canyon or on the floodplain of the Santa Ana River (Sycamore/Tequesquito Arroyo; Pigeon Pass), and relief along the margin of the incised fanhead trench varies be tween 50 and 75 feet (15 to 23 m). Small areas of the Canal surface are also found at the heads of westward and southward draining basins in the La Sierra Hills. It is associated with deeply weathered rock surfaces although the Vista Soil presently forming on this surface is not well developed. The Canal surface represents a period when earlier drainage across the Jurupa Hills was being actively dis sected by streams draining through the Arlington Gap. 158 Steep alluvial short fans of this age do exist on the north side of the Jurupa Mountains suggested that until this time the hills may have been buried in debris allowing no de velopment of T1 and T2 except as summit remnants and in obvious wind gaps which align with Lytle Creek today. Fans on the north side of the Jurupa Hills are partly buried under climbing sand dunes. Their toes are covered by re cent alluvial fan marginal sheetwash deposits derived from the major fans along the southern San Gabriel mountain flank. Limonite Ave. Surface (T4) This is a remnant surface preserved as a dissected alluvial fan on Limonite Ave. between Pedley and Rubidoux on the north side of the Santa Ana River adjacent to the Riverside Narrows (Figure 19, backpocket). In the Riverside area it forms residual flat topped hills at heights ranging between 840-850 feet (256 to 260 m). The slope varies be tween 5 and 8 percent. In the central Riverside area it is preserved as re sidual flat topped hills at heights ranging between 840 and 850 feet. No residual granite boulders are found on these surfaces. Throughout the La Sierra Hills this surface forms gentle sloping alluvial fans which extend up many small drainage basins. In the Corona area this is termin 159, ated abruptly by an en enchelon fault scarp system trending WNW along Parkridge Boulevard and the edge of Temescal Wash (Figure 3, backpocket). This surface is well developed around the southern margin of the Jurupa Hills. It is preserved as a dry valley along Armstrong Road. The northward extension of the Pedley Hills at the end of this valley may have been a critical factor in the preservation of this surface as to the south a small escarpment marks the boundary of this surface and a large embayment of the Riverside surface extends into Rubidoux (Figure 19, backpocket). This sur face now merges gradually with the Riverside/Pedley (T5, T6) surfaces on the north side of the Pedley Hills. On the margins of the Perris Block the surface forms an alluvial fan surface with slopes varying from . 2 to 8 percent. From Grand Terrace to Van Buren Ave. this can be mapped by a small escarpment varying in height between 5 and 6 feet (1.5 to 1.8 m). Streams have been deeply in cised into this surface and analysis of the sediment indi cates it is finer grained and more poorly sorted than pre sent day stream and river samples. Fanhead incision has dissected this surface, but this dissection may have occurred in several stages as two levels of discontinuous gravel terraces are preserved on the margins of Tequesquito Arroyo near Sedgewick Ave. and Chicago Ave. These coarse 16 0 , gravels are well weathered and embedded in a sandy matrix. Downcutting and stream bank undercutting in the narrow arroyo which is less than one quarter of a mile wide (0.40 km) has caused these gravels to be eratically preserved. The present stream is a misfit stream and would not be capable of creating this arroyo which increases in depth to 130 feet (40 m) near Chicago Ave. Near Chicago Ave. small drainage patterns are also evident on this surface forming shallow, broad valleys less than 10 feet (3.1 m) deep. These may have been associated with an earlier phase of downcutting prior to the recent dissection along several main drainage basins. West of Arlington Avenue an elongate series of small granite inselbergs, orientated in an east-west direction have acted as barriers to the dispersal of alluvial fan material. The Limonite Avenue surface is well preserved behind these inselbergs forming a smooth, gently sloping surface increasing from 2 to 8 percent slope as it ap proaches the Canal Surface. Streams are only incised 10 to 15 feet (3.1 to 4.6 m) into this section of the surface compared with the deep incision further east. It must be remembered that these streams do not drain into the Santa Ana River, but terminate on the Riverside Grand Terrace. Mockingbird Canyon which marks the eastern boundary of this section was an important drainage system for a por 1 6 1 ' tion of the Perris Block. This canyon also fails to reach the Santa Ana River and incision into the Limonite surface does not exceed 75 feet (23 m). Incision and fanhead en trenchment across the Riverside and Limonite Surfaces can be used as both a time and tectonic marker as this area responds to greater distance from major faults and changes in the location of the Santa Ana River. To the north of the inselbergs previously mentioned this surface is underlain by a series of fluvial deposited gravels immediately south of Indiana Avenue. These gravels rise abruptly 10 feet (3.1 m) and represent former flood- plain terrace deposits above the Riverside Grand Terrace Surface. Continuing west along the Arlington Gap there are other isolated surfaces near Loma Linda University's La Sierra Campus and within the Arlington Gap near Home Gardens. These surfaces represent areas where the Limonite Surface is represented as a floodplain fluvial terrace surface. In the areas previously mentioned it formed part of an extensive, now dissected, alluvial fan sequence. The Limonite Surface is associated with soils of the Arlington, Buren, Monserate and Ramona soil series. These are well developed soils associated with alluvial fan ter race deposits. 16*2 Riverside Grand Terrace (T5) This surface was first named by Eckis (1934) , but had been recognized as a major feature by Lippincott (1902) and Mendenhall (1905). It forms a prominent terrace along the Santa Ana River and is particularly well developed along Mt. Vernon Road as it ascends onto this surface. The height of this terrace is never less than 60 feet (19 m) above the Santa Ana and at Mount Vernon Road exceeds 140 feet (43 m). This surface extends from Grand Terrace through Riverside to Corona on the south side of the River and can .also be traced from Slover Mountain, Rubidoux and parts of Pedley on the north side (Figure 19, backpocket). The gradient of this slope is 1 to 2 percent and ranges in height from 1000 feet (310 m) at Grand Terrace to 650 feet (198 m) at Corona. Topographic and subsurface data (French, 1972) indicate an earlier drainage course of the Santa Ana River utilized the Arlington Gap. The Limonite Surface on the north side of the present position of the Santa Ana River is 'in grade1 to a river flowing through the Arlington Gap and not the present location of the Santa Ana. The height of the Riverside Grand Terrace is 7.80 feet (238 m) at Arlington and forms a divide between two dry valleys, both approximately 1 1/2 miles (2.4 km) wide; one a southwestward extension of the Riverside Grand Terrace Surface south to Corona, with a gradient of 1 per 163 cent in contrast to the initial 2 1/2 percent of the second valley which extends northward to merge with the Pedley Surface (T6) (Figure 19, backpocket). Residual hills and low terraces with flat tops at 780 feet (238 m) indicate the divide along this valley's northern and eastern margin (Figure 19). Northeast of Corona dissection of the Limonite Surface by streams flowing south to the Riverside Grand Terrace near Corona has created a series of broad shallow drainage basins which are partly beheaded by the present-day Santa Ana River. Possible topographic continuation of these earlier drainage channels have been deepened by southflow- ing streams which drain into the Santa Ana River today (Figure 3 and 19). Residual granite knobs northwest of Pedley attest to the former extent of this surface to the north prior to erosion to the Pedley base level (T6). Northeast of Stover Mountain on the north bank of the Santa Ana, former extensions of the Riverside Grand Terrace are buried beneath eolian Wisconsin dune sands. Small remnants of this surface also form isolated terraces on the northern margin of the La Loma Hills and Mt. Rubidoux (Figure 19). Mockingbird Canyon is in grade to and terminates on the Riverside Grand Terrace Surface, but this surface is now by-passed and deeply dissected by present day drainage which is in grade to the present Santa Ana River. (Free way design engineers in the Riverside area have made effec tive use of this entrenched topography to create freeway accesses utilizing this topography to its maximum benefit). The Riverside Grand Terrace forms a strath terrace adjacent to the Riverside Gorge but near Grand Terrace and Corona it forms a fill terrace. Several localities have been found with fossil soils - preserved below the Riverside Grand Terrace and are exposed on terrace slip-off surfaces. Soils of the Arlington, Buckenau and Porterville soil series are associated with the surface and many are relict soils. Active erosion of the Terrace is occurring along .... Riverside Drive, Corona where the Santa Ana River, until diverted in May 1981, was undermining the cliff. Eighty feet (24 m) of cliff retreat occurred between 1969 and 1980 (Leighton, 1980). This has created a fresh 80 foot (25 m) cliff exposing a series of fossil soils. Several large embayments occur along the margin of the Terrace on the south side. These steep slopes are now grass covered and gullied, but attest to active cliff erosion and under mining associated with meanders and shifts in the Santa Ana River within its floodplain area in the past. 165 Pedley Terrace Surface (T6) The Pedley Surface forms a broad flat plain on the north bank of the Santa Ana River. It extends north to the Jurupa Hills where it merges with the Riverside Surface and west to Prado Dam, a distance of 10 miles (16.1 km). To the north it is overlain by alluvial fan wash from the San Gabriels (MacKevett, 1951) and is eroded by streams graded both to the Mira Loma Terrace (T8) and the present Santa Ana River Floodplain. The concave backslope extends without a break to the Limonite Avenue Surface (T4) on valley interfluves and to the Canal Surface (T3) along the lower slopes of the Pedley Hills. This backslope probably represents a combined Pedley/Riverside Grand Terrace sur face. On the south bank of the river it forms a broad shal low 1 1/2 mile (24 km) wide embayment (Figure 19) which ex tends south to Arlington. This extension of the Pedley Surface represents a change in the course of the Santa Ana River prior to the gorge downcutting phase and post dates formation of the extensive Riverside Grand Terrace surface. Granite bedrock has controlled the development of this surface. Within the Narrows near to the Jurupa Railway Bridge granite is found within 6 feet (1.8 m) of the sur face. The Pedley surface is developed at 740 feet (226 m) in this section. West of the bridge the granite surface is 166 buried and many well developed fossil soils have developed. These have been exposed by later river entrenchment and the formation of the Mira Loma Surface (T8). Dissection of the slope by recent headward erosion of streams from the level of the Mira Loma and Santa Ana River floodplain has prevented soil accretion as slope wash colluvium has been diverted leaving the interfluves as relict surfaces. Lytle Creek Surface (T7) This surface is best developed on the north bank of the Santa Ana River east of the Rialto Bench and between Stover Mountain and the present location of Lytle Creek. A small remnant of this surface also exists on the south side of the Santa Ana River west of La-Loma Hills. The surface is composed of coarse fluvial sediments and sheet- wash deposits characteristic of distal alluvial fan de posits. This surface is 15 feet (4.6 m) below the River-., side surface adjacent to the Santa Ana River and represents ancestral shifting channel deposits of the Lytle Creek fan complex. These fluvial terraces are west of the San Jacinto fault zone. Intermittent uplift may account for the marked elevation break between the Lytle Creek and River-.. side surfaces. Sediments exposed in gravel pits are well defined graded thin gravels, coarse sands and silts de 167 posited under waning flood conditions. These deposits are subject to wind deflation and provided the sediment source for the eolian dune deposits which overlie and partly bury the Lytle Creek Surface. Wood fragments collected from channel sand sediments on this surface (Elders et al., - 1973) have been dated as 33,000 ± 900 years B.P. This sur face represents a major period of erosion in the adjacent mountains and depositions on the valley floor. This is now preserved as a fill terrace. Formation of this surface correlates with the influx of coarse material during an interglacial. Little wea thering of this coarse, gravelly material occurred and the Typic Xeropsamments of the Tujunga Series have poorly developed A horizons overlying bedded alluvial fan coarse sand and gravel beds (Soil Survey Staff, 1980). Mira Loma Fill Terrace (T8) This fill terrace is found at the junction of tri butary streams in the Pedley area and can be extended along most tributaries draining from the north for distances of 2 to 4 miles (3.2 to 6.4 km). This terrace is not pre served in the Riverside Narrows but dry valleys terminate about 15 feet (4.6 m) above river level and appear as hanging valleys today. These valleys are strongly con- % trolled by rock type forming V-shaped valleys on granite, 16 8 but broad swales near Mira Loma. The Mira Loma Terraces represents the deepening of those swales which are asso ciated with the Lytle Creek Surface. Today along Etiwanda Creek this fill terrace is being actively eroded. The Mira Loma Terrace represents a period of active entrenchment and valley broadened now preserved as a se quence. of dry valleys which grade into and merge with the recent alluvial fan wash originating from the San Gabriels. The combined depth of incision into the Pedley Surface exceeds 25 feet (7.6 m). These surfaces postdate the shift of the Santa Ana River into its present channel as ances tral stream courses extending to Norco have been beheaded by the Santa Ana. These ancestral stream valleys are re presented by a shallow broad valley system near Norco. The Mira Loma Surface represents a period of further deepening after the valleys had been formed during the ero sion and deposition of the Lytle Creek Surface. Along Tequesquito Canyon there are isolated remnants of two paired terraces preserved which could be correlated with the Lytle Creek and Mira Loma surfaces. Lateral migration of the present stream channel has resulted in imperfect preservation today. SOIL -DEVELOPMENT ON EROSION- SURFACES ? Standard field procedures were used for preparing the 16 9 soil descriptions, but it has been recognized that some pedogenic characteristics are more important than others in denoting relative ages of various soils (Birkeland, 1974; Yaalon, 1971). The more useful features include the color of the B .and C horizons, the type of epipedons pre sent, the amount of clay and the thickness of the B2t soil horizon (where present), the-degree of development of the subsoil (Cambic etc.). the characteristic of the C horizon, the type and degree of alteration of calcrete and silicrete horizons, and the degree of weathering of any pebbles in the C horizon (Appendix, Table 13). Recent channel changes along the Santa Ana River has resulted in undermining the exposure of new cliff sections near Hamner Bridge in Norco of the soil and sediments be neath the Riverside Surface. Road cuts on Van Buren Avenue have also exposed a short section of .the Pedley Surface. Gravel pits have been investigated near Stover Mountain where the Lytle Creek Surface has been exposed. Recent downcutting along many stream channels allows examination of several older surfaces in the Riverside area. Recent Soils and Associated Sediments Soils of the modern floodplain and eroded channels cutting the Mira Loma Terrace are loamy fine sands of the Dello series immediately adjacent to the flood channel and 170 sand flats (T10). Orangeville coarse loamy mixed soils are found on the Mira Loma Surface (T8) and high flood- plain terrace (T9). The sand hills area is associated with fine, wind eroded Xeropsamments of the Delhi soil series. Both the Dello and Grangeville series soils (Appendix, descriptions 0 and P) are grayish brown soils with an A/C profile. They can be distinguished by the average depth to the C horizon, A1, 7-10 inches (18-25 cm) Dello, and A1 10-17 inches (25-43 cm) Grangeville. Dello soils found on the floodplains are still subject to flooding and only a light litter of organic material has been contributed by the sparse vegetation. Soil development is immature and the soils have an ochric epipedon. Grangeville soils are not being eroded by flood waters, and a thick mollic surface horizon has formed. Grangeville soils merge with Hilmar loamy sands (Appendix III, N) as the Mira Loma Terrace Surface is traced away from the Santa Ana River along eroded valleys. Drainage is poor in these swales, and the A/C depth profile of the Hilmar resembles the Grangeville to a depth of 32 inches (81 cm) below which a Cca with fine lime veins is found. This reflects drainage and would also indicate a period of recent aridity. The surface soil of the Lytle Creek surface where it is not buried by sand dunes is mapped as gravelly loamy 171 sand of the Tujunga Soil Series. The dark grayish-brown surface layer and the C horizon are associated with 15 to 30 percent, gravel by volume. This gravel is horizontally bedded and gravel units grade upwards to thin cyclically bedded gravel and sand units which are similar to deposits currently being deposited in modern stream channels today. These soils are permeable and although roots can penetrate easily they do not support a dense vegetative cover. These gravelly soils represent late Wisconsin deposits yet the cyclical nature, coarseness, and high quartz content of the parent material has resulted in poor soil development. The fine sands of each fining upward sequence (Figure 20) were subject to wind deflation and the wind-blown material was included in the adjacent dune field. These deposits were laid down during the critical climatic change occurring between a pluvial glacial period and a dry interglacial. At this time climatic change results in vegetation changes allowing slipping of surface detritus and rapid alluviation of fan surfaces. Intensification of the arid climate during the interglacial and the large supply of detritus resulted in the formation of a major inland dune field across part of the Riverside and Lytle Creek Surface which has been tentatively dated as 23,000 years B.P. (Clarke, 1979). Dune field soils are highly permeable, low in nutri 172 ents and subject to further wind erosion. The Delhi soils are pale-brown (10YR 6/3) and do have an ochric epipedon (Appendix III, R). These dune fields were extensively re worked and subject to blowouts during the Xerothermic be tween 8,000 and 5,000 years B.P. At this time they did not receive any further sediment as the streams were already eroding 15 to 20 feet (4.6 to 6.1 m) below the dune sur-. face. Cienaba rocky sandy loam (Appendix III, E), character istic of all upland surfaces above the Canal Surface, is subject to rapid runoff and high erosion rates on 15 to 50% slopes. A typical Cienaba profile has a brown, coarse sandy layer ochric epipedon, 10-14 inches (25 to 35 cm) thick, underlain by a yellow-brown coarse sandy C horizon and at a depth of 26-30 inches (66 to 76 cm) weathered granite parent material. From these upland areas to the footslope of the Pedley surface on the south side of Santa Ana, a chronosequence is preserved by surface soils all associated with formation from granite parent material (Figure 21). This sequence is Cienaba rocky sandy loam, Vista Coarse sandy loam, Fallbrook sandy loam, Madera fine sandy loam, Monserate sandy loam, Buchenau loam, and Por-. terville Clay (Appendix III, descriptions E, F, H, K). This reflects a decreasing slope, zones of sheet wash ero sion, and deposition on a flat floodplain. This process is 173. FIGURE 21. Soil and topographic relationships Surfaces T1-T6. ZONE of DEPOSITION Area of periodic sheetwash deposition. Soil development on fine grained material. Cementation of coarse material and formation of duripan, prior to deposition of another cycle of sheetwash debris. Ramona sandy loam on surface. ZONE of EROSION Cienaba gravelly, sandy loam ZONE of ACCUMULATION CYCLE CYCLES OF SOIL EROSION INITIATED HERE BY-PASS ZONE Area of constant soil removal. If surface eroded by gullies, non deposition. Relict soil. Monserate. Subject to sheetwash erosion under semi-arid conditions. Debris removed periodically. High slope angle. Not found in Pedley area today. Fallbrook sandy loam near junction Pedley-Canal Surfaces may indicate this zone. 174 1 7 5 not active today, because headward erosion of streams below this surface have diverted sediment to the Santa Ana River, whose gorge also interrupts this sequence between the Mon- serate sandy loam and Buchenau loam soil series. Relict Soils Surface soils in the chronosequence previously des cribed (Figure 21*) are recognized as relict soils when they are related directly to the granite surface and have a very well developed soil profile when compared with other sur face soils in the chronosequence. The Monserate soils occupy a mid-slope position in the chronosequence and have a massive duripan C horizon. The., thick, hard, slowly permeable duripan, once established, would act to create a locally perched water table and encourage development of the mature soils above. The area on the Pedley surface where this soil develops is bounded by deep erosion chan nels to the east and west, and the Canal Surface above is not now receiving any sheetwash from the upland slopes. Prior to eroding of the Pedley Surface, this section of the slope would have been one of major movement and trans portation of coarse sediment. The Monserate soil also is found at the head of allu vial fans in Pigeon Pass where it is associated with the Canal Surface (T3). This soil is exposed in the entrenched 176 alluvial fan head channel walls. The massive duripan forms a resistant, prominent ledge which has resulted in deep narrow trenches with little lateral erosion occurring. Soils of the Buren series occupy similar locations on the Canal Surface and are preserved in fan head trenches f along Sycamore Canyon (Appendix III, G) and the upper sec tion, of the Limonite surface along Mockingbird Canyon. These areas are resistant to weathering. The prominent duripan formed under different climatic conditions when dissolved silica would be concentrated as soil moisture levels fluctuated around a narrow boundary. Also once a silica duripan is formed they act as an effective water barrier further concentrating dissolved silica. Fossil Soils Fossil soils are buried soils that may be exposed by roadcuts, housing development of cliff erosion. At least three fossil soils are exposed in many cut slopes under lying the Pedley Surface. Three vertical sections were described in detail: a) road cut junction Van Buren Avenue and Jurupa Avenue, south of the Santa Ana River (Appendix III, K); b) natural terrace slope between Limonite Avenue and 60th Street, north of the Santa Ana River (Appendix III, J); c) Hamner Bridge cliff section, adjacent to River Drive, Norco, south bank of the Santa Ana River (Appendix III, I); 17/7 Van Buren.Avenue The road cut exposes three fossil soils beneath the Buchenau loam forming on the Pedley Surface. They are separated by horizontal caliche zones and overlie a gravel filled channel cut into granite bedrock (Figure 22). The granite and stream channel represent the original landscape here buried 14 feet (4.3 m) below the Pedley Surface. The fossil soils are loams and contain little sand, suggesting original deposition as fine silts on a floodplain. The calcium carbonate may have been part of the suspended load deposited with the silt and concentrated by subsequent downward movement by leaching with the wetting front. This carbonate could be derived from ero- . sion of the limestone deposits near Crestmore and River- , side, suggesting that the river was flowing south across the Pedley Surface. Buchenau soils are developed over larger areas of the Riverside Surface and extend along the dry valley towards Corona through the Arlington Gap. The calcareous hardpan beneath the surface and fossil soils is truncated by the terrace slip-off slope adjacent to the gorge. This suggests that even the surface Buchenau loam is a relict soil. The 7.SYR hue of the surface soil and the 5YR B and C horizons is indicative of the age of this soil. 178 FIGURE 22. Cross-section of fossil soils exposed at Van Buren and Jurupa Road junction, Pedley. PEDLEY EROSION SURFACE JURUPA ROAD f B U C H E N A U L O A M R E L IC T S U R F A C E S O IL F O S S IL S O IL S £ ? S . < g T s T R E A M G R A V E L S £ & & & -&£>.£. ~ s---- / - « > . G R A N IT E VAN BUREN A V E . 135 fe e t I5-| 10 5H ft 0 4 3 1-2 I 0 m 41 m eters 179 180 60th Street Terrace A recent erosion scarp on the cut slope beneath the Pedley Surface exposes four fossil soils developed above silica cemented hardpans beneath the surface reddish-brown Ramona sandy loam (Appendix III, JO. These fossil soils are also reddish-brown sandy loams and have well developed B21 and B22 profiles; thick clay films; manganese stains; medium subangular peds. These fossil soils represent multiple accretions of eroded and transported sheetwash deposited near the base of an-erosion slope (Figure 21). The coarse grained material now formed into a duripan would represent material transported during heavy rains and the fine material "normal" erosion. Coarse debris accumulates on the surface under semi-arid climatic conditions, arid is rapidly trans ported to valley floors as sheetwash during short periods of intensive rain. This periodic flushing could account for the varying thickness of both the duripans and the fossil soils. The Ramona surface soil profile is not as well developed as the fossil soils and may have developed under differing climatic conditons or a shorter period of time. Hamner . Bridge - River Drive The cliff bluffs adjacent to the Santa Ana River in 1 .8 ,*1 the City of Norco have been subject to serious erosion due to recent course changes of the Santa Ana River. In 1969 5 0 feet (15.5 m) of bluff was lost along River Drive. An additional 6 feet (1.83 m) of the bluff was lost during the 1971 San Fernando earthquake and during the 1980 storms an estimated further 30 feet (9.3 m) of bluff was removed (Leighton and Associates, 1980). Similar rapid erosion rates are occurring near Alhambra Avenue, Norco. This., rapid erosion has provided fresh soil and sediment expos ures which can be studied from the base of the talus pile and measured using ladders and rock climbing techniques. This cliff section is approximately 300 yards long. The 80 foot (24 m) cliff can be divided into three sections (Figure 23). The upper 18 feet (5.6 m) is char acterized by a well developed surface soil and two fossil soils each associated with a calcium carbonate Cca horizon. The middle section between 18 feet (5.6 m) and 40 feet (12.4 m) is sandy silts with clay layers separating 7 inceptisols. This section can be further divided into an upper and lower section as thin Inceptisols in the upper section are associated with calcium carbonate accumulation in the C horizon. Carbonate forms both faint filaments and a few nodules indicating differentiation and the build up carbonate in materials originally low in carbonate (Gile and Grossman, 1979). The lower part of this section FIGURE 23. Vertical profile of fossil soils, Hamner Bridge cliff section. U P P E R C L IF F M ID D L E Hoploxeralfs B Floodplain Well developed Fo ttil Soils Entisols Al (1) 10 YR 2 /6 Bl (2) 10 YR 5/6 B2t (3) 7.5 YR 5/6 C (4) 10 YR 6 /4 Cca (5) 7.5 YR 5/6 HB2t (5A) 5 YR 5/3 Cco 95*5 ky (b) lEBI 10 YR 7/3 (7) C 10 YR 6/3 (6) Cca (BA) 10 YR 8 /2 H A (9) 10 YR 7/3 Cca 10 YR 6 /2 (10) 5.75m CI9’2“) C L IF F Inceptisols B Z A I (II) 10 YR 7/4 Cco 10 YR N7 (12) 3ZTA (13) 10 YR 6/4 Cco 2J5 Y 7/2 (I3A) SEA (14) 10 YR 7/4 Cca 2J5 Y 7/2 (15) B A (17 ) 2 5 Y 6/4 Cca 10 YR 6/1 (16) JTA 10 YR 7/3 (HBI) B 10 YR 6/3 C I0Y R 5/2 Caa 2 5 Y 7/2 X A 10 YR 7/4 (HB2) Bl 10 YR 6/6 B2 10 YR 6 /3 C 10 YR 7/4 XT A 25 Y 6/4 (HB3) Bl 10 YR 6/4 B2 10 YR 6 /3 C 10 YR 7/4 12m (40 ft) HAMNER BRIDGE CLIFF SECTION NORCO, CA. L O W E R C L IF F Fluviol deposits G R A IN S IZ E Erosional o * o * g s Channel Cobbles coated with carbon 20.) m (67 ft) gravel B cobbles sand silt B clay L IT H O L O G Y clay sand g o conglomerate carbonate S T R U C T U R E S // clay partings nodulor carbonate filam entous carbonate B A S A L C O N T A C T gradual clear abrupt erosional Soil hue and chroma as defined by Munsell ft 0 . .0 m 183 184 from 30 feet (9.2 m) lacks these carbonate horizons and is separated from the soils above by well defined zones asso ciated with thin clay partings (Figure 23). The lower section from 40 to 70 feet (12.2 to 21.4 m) consists of pebble, coarse gravel and sand units in which there are major fining upward sequences and many smalling fining sequences (Figure 23). The bottom of this section is * hidden by talus debris from recent cliff falls. The presence of three well developed paleosols asso ciated with a laminar and well developed nodular carbonate structure (Appendix III, I).indicates that these soils re present a long period of landscape stability (Butler, 1959; Gile and Grossman, 1979; Mulcahy, 1951), although periodic introduction of coarse debris provided fresh parent ma- __ terial and the burial of older soils. Clay accumulation, strong ped formation and color (2.5 YR) suggested that those soils were old and was verified when the caliche below upper paleosol I yielded a 234u date of 97,000 ± 5,000 years B.P. The overlying soil also has a B horizon suggesting a further period of colluvial deposition and soil formation prior to the incision of the Santa Ana River into the Riverside Grand Terrace. A graded carbonate coated gravel horizon at the base of this section may re present a point bar deposit and erosion of this horizon increases cliff erosion along vertical partings extending 185 upwards. The underlying Inceptisols represent poorly developed cambicw soils developing an overbank silty sands. Car bonate forms thin filaments and very soft nodules at the base of these smalls.-but they can form in 100-500 years (Gile and Grossman, 1979) and these soils represent fre quent floodplain events. The lower inceptisols are separ ated from those above by both a massive 4 inch (10 cm) thick carbonate horizon and a 24 inch (61 cm) zone of thin clay laminae alternating with 1 inch (2.5 cm) thick silt beds. Below this fissile unit two massive paleosols asso ciated with cambic B horizons and slight clay illuviation provide a distinctive basal unit to the upper cliff sec tion dominated by soil forming processes. These silty soils overlie 30 feet (9.2 m) of coarse gravel sand units. Individual graded units beginning with a granule or floating pebble horizon average 6 inches (15 cm) in thickness but are part of mega fining upward units averaging 3 to 6 feet (0.92 to 1.8m) in thickness. Two channel cut and fill structures are preserved but the limited exposure suggests a sequence of migrating channel gravel bars under transitional current flow conditions creating predominately laminar, graded horizons. Carbon coating of cobbles and pebbles forming low angle cross cutting beds between 57 and 60 feet (17.4 and 18.3 m) may 186 indicate a short period of intense runoff and floods fol lowing fire in the headwater of the channel. This cliff section represents a period of rapid runoff and removal of coarse debris from hillslopes as rainfall increases or tectonic uplift increases gradient and causes erosion. The first paleosol dated at 97,000 years B.P. overlies an equally well developed soilsuggesting a minimum time sequence of 200,000 years. Inceptisols and cambic horizons can develop with 100 to 1000 years (Yaalan, 1951) contrasting with the long period of landscape sta bility required to form argillic soils. Carbonates are only found in the upper section of the cliff and could in-., dicate the onset of more arid conditions as seasonal capil lary water concetrated carbonate in the zone of capillary water movement. Coarse pebble conglomerates, grading upward sequences and the many minor graded beds in the lower cliff suggest rapid erosion of the headwaters, and aggradation of the floodplain. The current was underloaded and could move coarse debris available on either steepened hillslopes following tectonic uplift or unstable slopes with a poor vegetation cover. This would correlate with increasing runoff at the beginning of a glacial stage. This cliff exposure indicates a major change in the paleohydrology and landscape stability of the region. 187 AGE DATING,AND DISCUSSION, Accumulation of pedogenic carbonate in semi-arid and 234 238 230 arid soils using U , U , Th measurements have en abled geomorphologists to span a critical time gap in dating techniques between 50,000 years B.P. and 500,000 years B.P. (Ku et al., 1979). Arid region pedogenic car bonates usually accumulate as massive, thick relatively pure horizons, often associated with carbonate coated pebble zones. Infrequent rains and relatively clay-free soils have combined to produce an environment where chemi cal leaching and contamination since the formation of the caliche horizons has been minimal. Soil carbonate was collected from the buried paleosol at Hamner Bridge at a depth of 10 feet (.31 m). Chemical leaching and the correction factor method of Ku et al. (1979) yielded a date of 97,000 ± 5,000 years B.P. 230Th = .593 ± .02 234 U 97 ± 5 t.y. 234 U = 1.115 ± .03 238u Although this soil is associated with clay loam, the clays may act as a perched water table preventing the dis solution of the carbonate. Recent exposure as the cliff retreats has also allowed the collection of fresh material uncontaminated by weathering and atmospheric dust. 1 8 8 The Hamner Bridge section is contiguous with Van Buren Avenue and other areas of the Riverside Grand Terrace Surface. Pedogenic carbonate horizons at Van Buren Avenue are associated with a sequence of buried soils and the sur face soil may represent a relict abandoned" surface as the lower Pedley Surface developed. * This regional correlation allows the Riverside Grand Terrace to be dated at approxi mately 100,000 years B.P. prior to a period of Wisconsin climatic cooling, dissection and increased tectonism. Attempts to date the second buried carbonate at Hamner Bridge produced results indicating a date older than hori zon IIC _ , but leaching and clay contamination prevented C a accurate dating. Carbonates at Van Buren Avenue have not been dated and may yield erroneous dates as they are road- cut exposures. Isolated radiometric dates can lead to erroneous in terpretations if considered in isolation from other re gional factors. Approximately 100,000 years B.P. surface dissection and erosion occurred in Cajon Pass associated with.climatic change and increased regional tectonism (John Foster; Ray Weldon, pers. comm.). The abandonment of the Riverside Grand Terrace Surface and development of the Pedley Surface would be a response to this regional tilting and the 97,000 year date on the carbonate horizon is an excellent correlation with this regional interpreta 189 tion. Soils are distinguished from each other on the basis of observable and measurable physical characteristices such as color, morphologic development and soil horizon thick ness. Field pedogenic characteristics for soil development on the erosion surfaces in the Riverside-Corona area is . . . . summarized in Table 2. The presence of strong, well de veloped argil lie horizons (Bt) on the older surfaces (T1-T6) contrasts sharply with the Wisconsin and Holocene surfaces. Typically these argillic soils are reddish and have a range of 7.5-5YR in the Munsell color notation. The older soils are also associated with well developed ped structure and thick clay film coatings on ped surfaces (Table 2). Two buried fossil soils in roadcuts and riverside cliffs near Riverside and Corona have also been identified by their argillic and calcic horizons. Pedogenic calcic horizons whether within surface soils or buried fossil soils, are not only indicators of soil age, but also cli matic change (Gile et al., 1979). It has been recognized that transitional stages of carbonate accumulation can in dicate the approximate age of soils. In sandy parent material, lime is first precipitated as disseminated lime filaments (Stage I). With increasing time lime nodules form and eventually become hard concretions (Stages II and TABLE 2. Field pedogenic characteristics showing soil development on erosion surfaces, northern Perris Block, western Riverside County, southern California. A-Horizon B-Horizon C-Horizon Surface Thickness (cm) Hue and Chroma Structure Thickness (cm) Hue and Chroma Structure Maximum Depth to top of C Horizon (cm) Hue and Chroma T1 0 - 36 10 y r 5/3 massive 36 - 104 5 y r 4/3 subangular blocky 104 7.5 yr 6/8 T2 0 - 2 4 7.5 yr 5/6 subangular blocky 24 - 81 5 y r 4/4 coarse subangular 81 7.5 yr 6/4 T3 0 - 6 7.5 y r 4/4 granular 61 - 109 5 yr 5/3 prismatic 109 10 yr 4/6 T4 0 - 15 10 yr 5/3 coarse granular 15 - 89 7.5 y r 6/4 angular blocky 35 10 yr 5/4 T 5 (l) 0 - 12 10 y r 5/4 granular b' 12 - 114 213 - 300 7.5 yr 5/6 5 yr 6/4 angular blocky prismatic 114 - 175 300 10 y r 5/6 7.5 yr 8/2 T6 0 - 2 4 10 yr 5/3 massive 24 - 101 7.5 yr 5/6 subangular blocky 101 7.5 yr 6/4 T7 0 - 10 10 yr 5/4 granular — — — 10 10 y r 6/2 T8 0 - 43 2.5 y 5/2 massive . — — — 43 2.5 y 7/2 T9 0 - 3 6 2.5 y 5/2 massive — — — 36 2.5 y 5/2 T10 0 - 15 2.5 yr 5/2 weak platy 15 2.5 yr 6/2 AO; ‘O'- 191 III). The final Stage IV, is the development of a massive carbonate accumulation zone as all the pore spaces become plugged. This prevents penetration of groundwater and causes the building upwards of a "laminar" zone.(Gile et al . , 1979). This horizon has been termed a "calcrete." Calcium carbonate is highly soluble and moves down wards in the soil profile to a particular depth under a given soil climatic condition. Under present day conditions surface soils of the Arlington, Buchenau and Ramona Series on the Riverside Surface are classified as Haplic Duri- xeralfs, Typic Durixeralfs, and Typic Haploxeralfs (Soil Survey Staff, 1971). These soils are associated with dis seminated lime rather than massive calcretes as in the fossil soils. By dating the upper fossil soil at Hamner Bridge at 97,000 ± 5,000 years B.P., it is suggested that some of thses soils developed in a period of 40,000 years prior to the abandonment of the Riverside/Pedley Surface. The presence of a second well developed fossil soil at Hamner Bridge and two well preserved fossil soils at Van Buren Avenue suggests these soils may be associated with an interglacial at approximately 20,000 years (Bergeren and Van Couvering, 1974). This long period of geomorphic stability separates a period of active uplift and a later period of regional tilting. During this period the Riverside Surface would 192 represent a broad floodplain and the Limonite Surface the adjacent alluvial fan sequence. 193 CHAPTER 6 TECTONIC ACTIVITY INTRODUCTION Average uplift rates along the south side of the San Gabriel Mountains range in value between 1 to 3 m/1000 years. Uplift along a fault zone is not continuous, but periods of rapid uplift are separated by periods of qui escence and landscape stability. Bedrock strath terraces may be formed and can correlate with these periods of stability but rapid denudation and increased sediment yield induced by climatic changes may mask these changes. The effects, timing and style of internal and mar ginal faulting must be consideraed when evaluated the con tribution of tectonic and climatic events to the develop ment of geomorphic surfaces. The impact of regional tec tonic events and the interaction of exceptional rapid de nudation of oversteepened mountain fronts must also be examined. INTERNAL FAULTING:(MOCKINGBIRD'CANYON FAULT) - The Mockingbird Canyon Fault was mapped by Rodgers (1965) as terminating near Lake Mathews (shown on Figure 3 as a solid black line). This study has mapped a minor splay fault extension of Mockingbird Canyon Fault as indi cated by the dotted line on Figure 3 by using a lineament 194 shown on the NASA overflight photographs (Sabins, 1978). Field checking indicates that the lineament correlates with a linear ridge and valley system, offset drainage channels and mid slope notches. A soil profile forming in this zone indicates no recent movement on this fault, but it was im portant during the mid-Pleistocene. This fault appears to have been important during the internal disruption of the Perris Block. Woodford et al. (1971) report that buried channel topography of the Surface divide along a watershed close to the trend of this fault. Preferential uplift has also occurred and the area to the east of the fault is 200 to 500 feet (62 to 155 m) higher than region to the west. There is a significant change in drainage direction along Mockingbird Canyon from E-W to NW-SE parallel to the fault. Preferential erosion along the fault as uplift occurred resulted in headward erosion and river capture. Along the border of the block increased gradient slowly shifted up stream eventually capturing a mature drainage system of relatively low relief on the Perris Surface. Todays drainage represents a classical misfit stream and although the alluvial fan sequence associated with the development of the Limonite Surface is large, the drainage does not extend to the Santa Ana River. This suggests that any fault movement on this fault terminated during or prior to the development of the Limonite Surface and recent up 195' lift has been dispersed along the marginal boundary faults of the Perris Block, the San Jacinto and Lake Elsinore Faults. BOUNDARY -FAULTING (SAW-JACINTO, AND ELSINORE FAULTS) In 1975, Sharp recognized.that the San Jacinto fault was comprised of an en echelon series of overlapping fault strands. Across the San Bernardino Valley these strands are the western Glen Helen Fault and the eastern Claremont Fault. Eckis (1928) proposed that uplift of the Rialto Bench had occurred and an area of downwarping would occur to the east as is evidenced by the continued subsidence of this southwestern corner of the San Bernardion Valley (Dutcher and Garrett, 1963). An elevation difference of 80 feet (24.8 m) exists between the Rialto Bench (Riverside Surface) and the present Lytle Creek increasing to 180 feet (55.8 m) when comparing the height of the Canal Surface at the mouth of Reche Canyon and the channel of the Santa Ana River. The Lake Elsinore Fault Zone is associated with a .. similar tectonic pattern. The unnamed fault which ruptures Holocene material along Temescol Wash and the edge of the research area has an accumulated relief of 60 feet (18.6.m). Strain between these two fault zones and differential 196 uplift has resulted in tilting of the landblock towards the west. Louis (1969) proposed that this type of crustal movement does not produce omnipresent dissection of a re gion, but valleys which run according to the gradient will be augmented in gradient and their streams deepened. Tri butaries which run nearly normal to the tilting are not altered in gradient and those which run against the tilting are diminished. The Santa Ana River trends parallel to the gradient of the differential tilting between these two fault sys tems. The study of the individual drainage basins which are normal to this trend also stress that maximum down- cutting and valley steepening occurred closest to the area of maximum uplift, Pigeon Pass and decreases and becomes negligible with increasing distance from the San Jacinto -fault zone as along Mockingbird Canyon. In the Pleistocene, a sequence of climatically con trolling events has also occurred involving downcutting, accumulation of alluvial deposits and secondary downcut-.. . ting. Erosion took place in the headwaters of drainage basins during the shift towards a new pluvial (glacial cycle) as increased surface runoff resulted in streams being unloaded with debris in relationship to their cri tical power of erosion. This period of downcutting would be terminated when surficial unstable slope material was 197 entrained and deposited on the floodplains of major streams. Slipping of the hillsides would continue until vegetation adjusted to the increased moisture and provided a greater vegetative density. Base level changes during maximum glacial sealevel lowering could induce a period of further downcutting. The change to dry interglacial conditions would imple ment a vegetation change to more flammable, oily, sclero- phyllous scrub vegetation and decrease in vegetative den sity. Periodic fires expose bare soil which would be re moved during debris accumulated on the hillslopes during the pluvial period in short episodes of intensive erosion. This would cause aggradation and valley fill deposition. Later removal of the accumulated debris can expose bare rock surfaces, further reducing vegetative cores, but now increasing the critical power of stream erosion as surface runoff increases but load decreases. This can also be in duced by increased urbanization and farming techniques re sulting in degradation of valley fill deposits. A strath terrace associated with stream gravels and thick soil sequences records a period of landscape sta bility. The Riverside Grand Terrace (T5) records such a period of stability and carbonate 234^ provides a minimum date of 97,000 ± 5,000 years B.P. for the upper buried paleosol. Mockingbird Canyon is graded to this surface but 1,98 Sycamore/Tequesquito Canyon and Pigeon Pass now bypass this surface and are entrenched 70 to 80 feet (21.7 to 25 m) into.the Riverside Surface. This suggests that the erosion of the Riverside Narrows Gorge and entrenchment below the Riverside Surface is largely the result of intermittant tectonic tilting within the San Jacinto fault, associated with tectonic warping. This coincides with the increased tectonic activity noted by Foster (1980) in the last . . 100,000 years and associated with the headward erosion of Cajon Creek resulting in capture of stream drainage pre viously draining south and east into the Mojave basin. The present course of the Santa Ana River through the Riverside Narrows into the Prado Basin is 24 percent shorter than a course through the Arlington Gap. Although this may represent a natural course shortening, associated with flood crevasse splaying and abandonment of a meander loop it could also represent course adjustment to an in creasing tectonic induced gradient. Uplift has also occurred in the wedge-shaped junction of the Chino-Elsinore-Whittier faults where White (1976) has determined 450 feet (139.5 m) of uplift has occurred in the last 70,000 years. Temporary drainage disruption and the growth of the Corona alluvial fan as uplift of the Santa Ana Mountains occurred may also be contributory fac tors to the shift of the Santa Ana River from the Arlington 199 Gap into its present course. This northern area of the Perris Block therefore re presents an area of structural stability surrounded by areas of active uplift. Assuming that the Limonite and Riverside Grand Terrace were initiated during the last 200,000 and are the equivalent of the Oxygen-Isotope Stages 5 and 6 , uplift prior to that date was approximately two feet per Ky (0.61 m Ky) . At Hamner Bridge the 97,000 year B.P. fossil soil provides an horizon which can be correlated with the extensive Riverside Grand Terrace. This surface at Grand Terrace is presently 140 feet (43 m) above the Santa Ana River. This indicates an uplift rate of 1.4 feet Ky (.43 m Ky) along the Claremont branch of the San Jacinto Fault Zone. These low rates are in marked contrast to other areas of southern California and suggests that the Perris Block is a stable buffer zone between areas of active tectonism and may also be an important pivot block in the San Bernar dino area. 200 CHAPTER 7 SUMMARY AND CONCLUSIONS The mid-Pleistocene Pasadenan orogeny was the culmina tion of a period of tectonic activity involving uplift, tilting, block rotation, thrust and strike slip faulting, and folding which created the Transverse Ranges. Disrup tion of earlier geomorphic landscapes and the rejuvenation of the Perris Block granitic terrain provided a sediment source and changes in erosion thresholds resulting in a complex interplay of synorgenic deposition separated by periods of landscape stability. Pleistocene climatic changes have added a further dimension as vegetation, in creases in sediment yield and pronounced changes in runoff have resulted in periodic rapid denudation processes operating throughout the region. A synthesis of the interrelationship of climate, re gional tectonics and geomorphic events is presented in Table 3. The following discussion which is presented in reverse chronologic order (youngest to oldest expands this table and relates soil morphogenesis and geomorphic sur faces to these regional changes). 1800 to the Present Day: Surface TIP During the past 130 years the San Bernardino valley and the Riverside area has undergone a marked change in TABLE 3 CORRELATION OF GEOMORPHIC, CLIMATIC AND TECTONIC EVENTS IN THE RIVERSIDE-CORONA AREA TIME GLACIAL CLIMATE GEOMORPHIC EVENT TECTONIC EVENTS POSITION OF SANTA ANA RIVER HOLOCENE 0-10,000 Mathes Peak Recess Peak Xerothermic Pluvial Pluvial Intense Aridity Pluvial Recent erosion last 200 JJ^O years associated change from natural vegetation to agriculture. Renewed period of erosion ^ Vegetation change. Dune field blowouts. Period of backfilling. Sea level rise. Large alluvial fans from San Gabriel Mountains. T8 Erosion. Continued uplift of San Jacinto Fault. Remained in present position through the Riverside Narrows. W ISCONSIN 10,GOO- 75, 000 Tioga 13,000- 22,000 Max. 17,000 Tahoe 70,000 Pluvial Interpluvial Dry Pluvial Deposition of coarse Jg alluvial fan deposits. Large dune fields develop on Wisconsin Surface -22,000 T7 Abandonment of Pedley/ Riverside Surfaces. Erosion of Riverside Narrows. Erosion and formation of Proto-Cajon Valley, change to westerly drainage approx imately 80,000 years B.P. Westerly tilting of Perris Block between San Jacinto and Elsinore Faults. Uplift of Chino Hills, west of Elsinore Fault,140m. Erosion of Riverside Narrows associated with Tahoe low sea level and regional tilting. SANGAMON 75,000- 128,000 Interglacial Dry Tilting results in shift of Santa Ana River. Development of Pedley Surface. Formation T6 of carbonate horizons. Continued uplift of Chino Hills. Westward tilting of Riverside Surface as uplift renewed on San Jacinto Faults. Shift of drainage Abandonment of Arlington Gap and development of Pedley Surface. 201 TABLE 3 CONTINUED TIME GLACIAL CLIMATE GEOMORPHIC EVENT TECTONIC EVENTS POSITION OF SANTA ANA RIVER LATE IL L IN O IS 125,000- 200,000 Manunouth Lake Tills Pluvial Periodic erosion of coarse debris. Deposited T5 on floodplain. Multiple fossil soils form T*» Period of tectonic stability. Removal and deposition of coarse gravels associated with regional tilting of 10-12 degrees northeast of San Gabriel and San Bernardino Mountains. Drainage through the Arlington Gap into Corona area. Growth of alluvial fans from San Gabriels forced river to southern margin of vlalley. Possibly buried river channel associated with tnaximum lowering of sea level. MIDDLE AND EARLY. IL L IN O IS 200,000- 500,000 Illinois Interglacial & Glacial Donner Lake Basin Tills Interglacial Dry Pluvial Intense erosion. Disruption ^ of fans extending from San Gabriels onto Perris Block. Bedrock strath surfaces J2 form on Jurupa Hills and Perris Block as sediment removed. T1 Contraction of adjacent areas. 10 km offset on San Andreas F. Folding and uplift on northern flanks of San Gabriel Mts. Pasadenan Orogeny. Possibly drainage through Spadra Gap. Uplift and development of fan systems caused drainage shift to the southern margin of area PRE 500,000 Yarmouth Interglacial Dry Period of deep weathering. Alluvial fans from San Gabriel Mountains extend onto Perris Block. Formation of surfaces on high portions of the Perris Block. Plio/Pleistocene Surfaces of Perris Block. Pleistocene Time Scale: Berggren and Van Couvering, 197M. Tectonic Data: Foster, 1980 ZOZ 203 agriculture and population. In 1862 coincidence of growth, deforestation, development of front row crop agriculture and a major flood event resulted in valley degradation and an intense scouring event which can still be recognized on the present floodplain. This flood effectively removed some species of native vegetation from the floodplain and lower water tables has not allowed them to become re-estab lished. Successful competition from introduced weedy species has further changed the floodplain flora. Periodic scour during extremely wet seasons causes shifts in the Santa Ana River channel. The floodplain is degrading during these periods, but subsequent aggradation suggests that the modern floodplain is near equilibrium under the present runoff conditions. The present floodplain is ap proximately 3 feet lower than T10 which reflects decreasing sediment yield and degradation as flood control, floodplain management and urbanization reduce overall sediment yield. Natural vegetation and hillslope.cover is also being de stroyed by housing and off-road vehicles so that hillside degradation and gullies are being developed or renewed at the present time. Holocene and Xerothermic 10,000 - 1800's Within the Riverside Narrows remnants of Terrace 9 can be correlated with small alluvial cores which infill 204 broader areas of the floodplain. The Holocene is a major period of backfilling along the Santa Ana as sea level rose after the Wisconsin low. This valley aggradation was in tensified by the Xerothermic and period between 8,000- 5,000 B.P. Vegetation was reduced on mountain slopes and initiated a period of intense erosion as deeply weathered material formed under moist pluvial conditions during the Tioga, late Wisconsin glacial event was removed. This debris was deposited on the floodplains causing alluviation as streams were unable to move the sediment. This period was also accompanied by a period of dune field modifica-.. tion. Streams were already entrenched below the dune sur face and no longer supplied the dune field with sediment. Vegetation changes left the dunes without a stabilizing ground cover initiating a period of reworking and asso ciated dune blowouts. Entrenchment had occurred during the last part of the glacial pluvial cycle when sea level was at a maximum depth and the valley slopes had equilibrated under the more humid conditions and denser vegetative cover. This was accom panied by in situ weathering and periodic, intense rains degraded the valley fill surfaces. These fill terraces are comprised of coarse gravels and soils are poorly developed on these surfaces. Con tinued elevation along the San Jacinto fault resulted in <205 10 to 15 feefcj .(3 to 4.6 m) of incision. This rate is com patible with similar rates throughout southern California. Wisconsin 75,000-10,000 years B.P. This time span marks a period of more intense tec tonic activity in the San Bernardino area. Erosion and formation of a proto-Cajon Valley developed as a result of regional tilting renewed faulting and uplift occurred along the San Jacinto fault adding a tectonic gradient element to the normal longitudinal gradient of the Santa Ana River. This resulted in abandonment and course shortening of the Santa Ana River and the incision of the river into a bed rock saddle through the Riverside Narrows. This could also have been accelerated by glacial lowering of sea level during the early Wisconsin Tahoe stage (60,000-75,000 years B.P.). This bedrock gorge has persisted as the main drainage of the Santa Ana River since this time and has been periodically scoured during periods of glacial sea level lowering. (The present gorge has approximately 100 feet [31 ml of fill.) The beginning of this glacial cycle is marked by major erosion in the upper reaches as a new pluvial cycle is initiated. This would be enhanced by the tectonic events and caused major mid-fan entrenchment. Streams closest to the fault zone were the most deeply incised but as the '206 Arlington Gap had been abandoned by this period streams in the western region were not so deeply eroded. Under pluvial conditions deep weathering of the valley slopes continued but the period of stability associated with this period is masked by continued erosion. At the end of this pluvial the change in vegetation and the run off conditions initiated a major period of valley aggrada tion and fan growth from the San Gabriels and San Bernar dino Mountains. Sediment was stripped from the latter mountains and was deposited as large alluvial fan complexes. This period of aggradation was intensified by the growth of Cajon Fan along the Proto-Cajon Valley and Lytle Creek Fan as con tinual uplift of the San Jacinto fault increased the gra dient of the head of this fan and causing aggradation of the lower fan surfaces. This is preserved as the Lytle Creek Surface. Shifting channels on this surface probably reflect periods of incision and entrenchment near the fan apex as tectonic uplift along the fontal faults continued. The periodic sedimentation on this fan provided thin fining upward gravel-sand sequences. This deeply weathered material was removed from the hillsides and towards the end of this interglacial provided the sediment source for the Sand Hill\s dunefield. Massive_longitudinal dunes formed orientated parallel to the wind funnel gap through Cajon 2 0 7 Pass. This field extended to the Santa Ana River which was probably undercutting the northern margin of the La Loma Hills as is evidenced by the truncated alluvial fans and steep bluffs which vary in height between 120 to 180 feet (37 to 60 m) along the edge of the Riverside Grand Terrace. This dunefield became stabilized by vegetation around 22,000 years B.P. as the climate became wetter at the beginning of the Tioga glacial stage. This glacial stage is again masked by headward erosion causing downcutting and by-passing of the Lytle Creek Sur face. This would be associated with base level change and scour through the Riverside Narrows. This downcutting was terminated when slopes equilibrated with the new conditions and superficial material was entrained on the valley floor. The Mira Loma Surface is lower than the Lytle Creek Surface and can also be identified by ranging valleys in the River side Narrows. Further erosion towards the end of the Tioga resulted in abandonment of this surface.' In the area to the west of Corona and the Chino/Elsin ore/Whittier faults tectonic movement resulted in over 400 feet (122 m) of uplift. This produced a sequence of four terraces preserved in the Santa Ana Canyon. This movement resulted in growth of the Corona Fan and provides a con trast to the uplift and tilt of the Perris Block which averaged only 1 . 4 feet. (.^31 m)/1000 years in this area. 208 Sangamon - Early Illinonian 75,000-200,000 years B.P. The Sangamon Interglacial and early Illinois are char- aterized by a period of deep weathering and structural stability. Drainage was across the Riverside Grand Terrace Surface for most of this period with drainage through the Arlington Gap. Early tilt motion of the area between the boundary faults around .90,000 years B.P. resulted in the abandonment of the Arlington Gap and the initial change in flow towards the Pedley area. This may have occurred as a meander loop development and only later became the shortened course associated with the development of the Riverside Narrows. The development of the Narrows could be interpreted as river capture but this would not account for the Pedley embayment which joins the Riverside Surface near Arlington. The Riverside stage represents the maximum stage of valley widening and a long period of landscape stability. Drainage from the Jurupa and Pedley Mountains may have been further downstream and lenses of sheetwash would be graded to this more distant base level. The proto-Santa Ana drainage was controlled by new exhumed bedrock islands of earlier periods of landscape erosion. Drainage during the development of the Riverside surface would have been pre dominantly through the Arlington Gap to Corona. The dis tribution of the more alkaline Buchenau loam along this 209 water gap corroborates this drainage pattern as the lime would be derived from the erosion of residual limestone islands around Crestmore. Thick caliche zones and duripans between soils de rived from the sheetwash and fine grained alluvial de- : posited as the floodplain during flood stages indicate this plain was being aggraded during semi-arid climatic conditions. Fine floodplain deposits also indicate that the source of this material had also undergone a long period of deep weathering or that coarse sediment was being trapped in local drainage tributaries and was only peri odically deposited on a stable geomorphic terrace surface. A carbonate horizon beneath a buried paleosol has been dated as 97,000 ± 5,000 years B.P. Beneath this soil is a second well developed paleosol. The intense red soils indicate that they have undergone a long period of mor phogenesis. Beneath these soils floodplain silts and fine sands associated with thin Inceptisols are exposed. These deposits indicate periodic lateral overbank deposi tion with some soil formation during short periods of non deposition. The coarse, well weathered fining upward cobble, gravel and san horizons form the basal unit of this section. This section indicates that during the formation of the Riverside Grand Terrace Surface there was a period of 210 rapid deposition and erosion associated with streams cap able of rapid erosion and frequent floods. As climatic conditions changed the floodplain became one of lateral scour and strath terraces development. This was followed by a long period of structural stability and soil forma tion. A buried channel beneath the Arlington Gap may be associated with maximum sea level lowering followed by channel aggradation during the Illinoian glacial stage. Illinois Interglacial and Early Illinois Glacial 20Q,000-500,000 years B.P. Prior to the Pasadenan Orogeny alluvial deposits con taining fragments of Pelona Schist indicate that large fans extended from the San Gabriels across the Jurupa Hills and onto the Perris Block. Intense deep weathering occurred during this period. These fans were disrupted by folding, uplift, and erosion on the frontal faults of the San Gabriel and San Bernardino Mountains. Intermittent uplift resulted in the development of two concordant summit surfaces on the Jurupa Mountains and two bedrock'strath surfaces on.the Perris Block. These surfaces may also have been pediment surfaces which have now been exhumed and all sediment cores removed. Continued uplift resulted in the formation of two smaller alluvial fans cycles and the storage of sediment stripped from the 211 Perris Block. Periods of tectonic uplift caused incision and fan head entrenchment of the alluvial fan sequences. The removal of this sediment from this one small area of an inland basin within the Los Angeles Basin assuming that the sediment was already deeply weathered involves a 3 sediment packet of approximately 72 km . This yields a net erosion rate of one cubic meter of sediment per 1000 years but uplift was approximately . 61 m per 1000 years resulting in a net loss of sediment of approximately 30 3 cm per 1000 years. The Los Angeles Basin was rapidly filled after the Pasadenan Orogeny and the arrival of large amounts of sediment in the inner basins of the off shore Continental Borderland, the San Diego Trough and the San Pedro Basin has been estimated at 250,000 years B.P. (Nardin, 1981). This time gap stresses that there is always a time stratigraphic lag in depositional response systems. Alluvial fan sequences have large sediment stor age capacities. Climatic changes and the formation of bed rock surfaces as sediment is stripped off hillsides may provide a critical factor in this sediment movement process as bedrock expose increases surface runoff, decreases the load of streams in their upper reaches resulting in the ability to erode and transport sediment downstream. Vertical tectonics were a major factor in the evolu tion of the central Transverse Ranges during the Quatenary. 212 Depositional and geomorphic sequence of events in the Corona/Riverside regions records the effects of synorogenic events and the interplay of climatic events. Changes in the hill slope environment can result in increased erosion capacity of streams and subsequent aggradation in their lower reaches. The area is also unique in that it records a long period of structural stability during the late illinoian and Sangamon period (200,000-70,000 years B.P.). A large amount of material had been generated by this region prior to this time to provide the influx of a sediment 'packet' into the Continental Borderland. Buried fossil soils and caliche deposits dated at 97,000 ± 5,000 B.P. using 234^ dating techniques provide important stratigraphic control on the development of this surface. This time marker allows interpretation of post-depositional erosion and tec tonic history. Continued uplift and tilting between the boundary faults of the Perris Block, the San Jacinto and the Lake 4 Elsinore fault during the past 75,000 years have preserved this surface. This tilting parallel to the trend of the Santa Ana River has resulted in entrenchment and the de velopment of a shallow bedrock gorge through a granitic area. This tectonic tilting has also isolated Wisconsin surfaces developed as a response to rapid changes in hill- 2 i f 3 slope environments during profound climatic changes in the San Gabriel and San Bernardino Mountains. Intense periods of aridity can dramatically change vegetation allowing hillsides to be stripped of their weathered material either as climate becomes increasingly humid or during short periods of heavy rain. This landscape was virtually 'fossilized' after the Xerothermic until the arrival of large numbers of settlers in the 1850's. The change from aboriginal nomadic seed gathering and later mission ranching to modern row crops and irrigated orange groves increased runoff causing recent degradation along the Santa Ana River. Mediterranean Climate is characterized by short inter vals when the rainfall is above average and several years of below average rainfall. Intense rainfall can cause severe flooding and erosion when combining with increased runoff whether due to deforestation, fires, urbanization or farming practices. In 1862, a record flood combined . . with these factors wrecked havoc in the valley. Today, the Santa Ana River is controlled by major flood control dams, but the floodplain is increasingly being used for commercial purposes. The San Jacinto fault is considered to be one of the most active faults in southern California capable of generating an 8 on the Richter Scale. The landscape of this region is dynamic not static, but can be 214 altered dramatically by bulldozers, and off-road vehicles as well as natural forces. 215 REFERENCES Allen, J.R.L. and Collinson, J.D., 1974, The superimposi tion and classification of dunes formed by unidirec tional aqueous flows: Sed. Geology, v. 12, p. 99- 130. Andrews, P.W., 1972, Ecology of a southern California floodplain (Ph.D. Thesis): Claremont Graduate School, 300 p. Armstrong,R.L., and Suppe, J., 1973, Potassium-Argon geo chronology of Mesozoic igneous rocks in Nevada, Utah, and southern California: Geol. Soc. America Bull., v. 84, p. 1375-1392. Aschmann, H., 1959, Evolution of the wild landscape and its persistence in southern California: Annals Assoc. American Geographers, v. 49, p. 34-57. Atwater, T., 1970, Implications of plate tectonics for the Cenozoic evolution of western North America: Geol. Soc. America Bull., v. 81, p. 3513-3536. Axelrod, D.I., 1958,tEvolution of the Madro-Tertiary Geo- flora: Bot. Rev., v. 24, p. 433-509. Baird, A.K., Morton, D.M., Woodford, A.O., and Baird, K.W., 1974, Transverse Range Province: A unique structural and petrochemical belt across the San Andreas Fault System: Geol. Soc. America Bull., v. 85, p. 163-174. Barrows, A.G., 1979, Geology and fault activity of the Valyermo segment of the San Andreas Fault Zone, Los Angeles County, California, California Div. Mines and Geology Open-file Report 79-1 LA, 4 9 p. Bartholomew, M.J., 1979, San Jacinto fault zone in the northern Imperial Valley, California: Geol. Soc. America Bull., v. 81, p. 3161-3166. Bauer, B., 1980, Drainage density - An integrative measure of the dynamics and the quality of watersheds: Z. Geomorph. N.F., v. 24, p. 261-272. Beattie, G.W. and Beattie, H.P., 1939, Heritage of the valley: Pasadena, San Pasqual Press, 459 p. 216 Berggren, W.A., and Van Couvering, J.H., 1974, The late Neogene; biostratigraphy, geochronology and paleo- climatology of the last 15 million years in marine and continental sequences: Palaeogeogr., Paleao- climatol., Palaeoecol., v. 16, p. 1-216. Birkeland, P.W., 1974, Pedology weathering and geomorpho- logical research: London, Oxford Univ. Press, 285 p. Birkeland, P.W., Crandell, D.R., and Richmond, G.M., 1971, Status of the correlation of Quaternary stratigraphy in the western conterminous United States: Quater nary Res., v. 1, p. 208-227. Blackwelder, E.G., 1927, Fire as an agent in rock weather ing: Jour. Geology, v. 35, p. 134-140. . ____ , 1931, Pleistocene glaciation in the Sierra Nevada and Basin Ranges: Geol. Soc. America Bull., v. 42, p. 865-922. Blake, W.P., 1856, Geology of the route for a railroad to the Pacific examined under the command of Lieutenant R.S. Williamson in 1853 under the direction of Jeffer son Davis, Secretary of War: U.S. Senate, 33rd Con gress 2nd Session, S. Ex. Document 78, 370 p. Bolton, E., 1930, Anza's California Expeditions, volume 1: Berkeley, Uni. Calif. Press, 529 p. Bull, W.B., 1979, Threshold of critical power in streams: Geol. Soc. America Bull., v. 90, p. 453-464. Burke, R.M., and Birkeland, P.W., 1979, Re-evaluation of multiparameter relative dating techniques and their application to the glacial sequence along the eastern escarpment of the Sierra Nevada: Quaternary Res., v. 11, p. 21-51. Butler, B.E., 1959, Peridic phenomena in landscapes as a basis for soil studies: C.S.L.O., Australia, Soil Publ. no. 14, 20 p. Cabelleria, J., 1902, History of the San Bernardino Valley from the padres to the pioneers, 1810-1851: San Bernardino, Times Index Press, 130 p. Cant, D.J., and Walker, R.G., 1978, Fluvial processes and facies sequences in the sandy braided South Saskatch ewan River, Canada: Sedimentology, v. 25, p. 625-648. ,217 Chorley, R. J. , 1957, Illustrating the laws of morphometry: Geol. Mag., v. 94, p. 140-150. Clayton, J.L. , and Arnold, J.F., 1972, Practical grainsize, fracturing density and weathering classification of intrusive rocks of the Idaho Batholith: U.S. Dept. Agriculture Forest Service Gen. Tech. Rept. INT-2, 17 p. Clayton, J.L., Megahan, W.F., and Hampton, D., 1979, Soil and bedrock properties; Weathering and alteration products and processes in the Idaho Batholith: U.S. Dept. Agriculture Forest Service Research Paper INT-237, 34 p. Clarke, A.O., 1978, Quaternary evolution of the San Ber nardino Valley: Quart. San Bernardino County Museum Assoc., v. 26, 144 p. _________, 1980, Geomorphology and Quaternary history of the Sand Hills, San Bernardino Valley, California: Quart. San Bernardino County Museum Assoc., v. 27, 85 p. Collinson, J.D., 1970, Bedforms of the Tana River, Norway: Geogr. Ann., v. 52A, p. 31-55. Crowell, J.C., 1962, Displacement along the San Andreas fault, California: Geol. Soc. America Spec. Paper 71, 61 p. Culling, W.E.H., 1957, Equilibrium states in multicyclic streams and the analysis of river-terrace profiles: Jour. Geol., v. 65, p. 451-467. Daubenmire, R., 1968, Plant Communities: New York, Harper and Row Pub. Co., 300 p. Davis, E.L., 1978, (Ed.), The Ancient Californians; Rancholabrean hunters of the Mojave Lakes County: Nat. History Museum of L.A. County, Science Series no. 29, 193 p. Davis, W.M., 1909, Geographical Essays: Boston, Mass., Ginn Publishing Company, 777 p. Dibblee, T.W., Jr., 1975, Late Quaternary uplift of the San Bernardino Mountains on the San Andreas and related faults: California Div. Mines and Geology, Spec. Rept. 118,; p. 127-135. 21'8 Doehing, D.O. , 1968, The effects of fire on geomorphid pro- cesses in the San Gabriel Mountains, California: ConT trib. Geology, v. 7, p. 43-65. DoornKamp, J.C. and King, C.A.M., 1971, Numerical analysis in geomorphology; an introduction: London, Edward Arnold Ltd., 372 p. Dudley, P.H., 1936, Physiographic history of a portion of the Perris Block, southern California: Jour. Geology v. 44, p. 358-378. Dutcher, L.C., and Garrett, A.A. , 1963, Geologic and hydro logic features of the San Bernardino area, California, with special reference to underflow across the San Jacinto fault: U.S. Geological Survey Water Supply Paper 1419, 114 p. Elders, W.A., (Ed.), 1973), Geologic investigations of the San Jacinto fault zone, and aspects of socio-economic impact of earthquakes in the Riverside-San Bernardino area: Riverside, Univ. Riverside Press, Riverside Musuem Contributions no. 3, 129 p. Emery, K.O,, 1947, Asymetrical valleys of San Diego County, California: Bull. Southern California Academy Sciences, v. 46, p. 61-71. English, H.D., 1953, Geology of the San Timoteo badlands, Riverside County, California (M.S. Thesis): Claremont Graduate School, 96 p. English, W.A., 1926, Geology and oil resources of the Puente Hills region southern California: U.S. Geo logical Survey Bull. 768, 110 p. Eckis, R., 1928, Alluvial fans of the Cucamonga District: southern California: Jour. Geology, v. 36, p. 225- 247. _________, 1934, South Coastal Basin Investigation, geology and groundwater storage capacity of valley fill: California Dept. Public Works, Div. Water Resources Bull. 45, 273 p. Evernden, J.F., and Kistler, R.W., 1970, Chronology of em placement of Mesozoic batholith complexes in Califor nia and western Nevada: U.S. Geological Survey Prof. Paper 623, 42 p. '219 Foster, J.H., 1980, Late Cenozoic tectonic evolution of Cajon Valley, southern California (Ph.D. Thesis): Univ. California Riverside, 238 p. French, J.J., 1972, Groundwater outflow from the Chino Basin, upper Santa Ana Valley, southern California: U.S. Geological Survey Water Supply Paper 1999-G, 15 p. Frye, J.C. and Leonard, A.R., 1954, Some problems of allu vial terrace mapping: Am. J. Sci. , v. 252, p. 242-251. Gaede, V.F., 1969, Prado-Corona oil field: California Oil Fields - Summ. Operations, v. 55, p. 23-29. Gile, L.H., and Grossman, R.B., 1979, The desert project soil monograph; soils and landscapes of a desert region astride the Rio Grande Valley near Las Cruces, New Mexico: U.S. Dept. Agriculture, Soil Conservation Service, 984 p. > Gray, C.H., Jr., 1961, Geology and mineral resources of the Corona South Quadrangle: California Div. Mines and Geology Bull. 178, 120 p. Gregory, K.J. and Gardiner, V., 1975, Drainage density and climate: Z. Geomorph. N.F., v. 19, p. 287-298. Haner, B.E., 1975, Soils, paleosols and geomorphological relationships of erosion surfaces and Santa Ana River terraces near Pedley, Riverside County, California: Unpublished Rept., Soil Stratigraphy USC-600, 34 p. Hawkins, J.W., Jr., 1970, Petrology and possible tectonic significance of late Cenozoic volcanic rocks, southern California and Baja California: Geol. Soc. America Bull., v. 81, p. 3323-3338. Hefley, H.M., 1937, Ecological studies on the Canadian River floodplain in Cleveland County, Okalahoma: Ecol. Mong. no. 7, p. 345-402. Hettner, A., 1928, The surface features of the land: New York, Hafner Publishing Company, 193 p. Horton, R., 1932, Drainage basin characteristics: Trans. Americal Geophys. Union, v. 13, p. 350-362. _________, 1945, Erosional development of streams and their drainage basins: Geol. Soc. America Bull., v. 56, p. 275-370. 22,0 Howard, A.D., 1959, Numerical systems of terrace nomencla- .. ture; A critique: Jour. Geology, v. 67, p. 239-243. Howell, J.T., 1929, The flora of Santa Ana Canyon region: Madrono, v. 1, p. 243-253. Iverson, R.M., Hinckley, B.S., and Webb, R.M., 1981, The physical effects of vehicular disturbances on arid landscapes: Science, v. 212, p. 915-917. Jackson, M.L., 1965, Clay transformation in soil genesis during the Quaternary: Soil Sci., v. 99, p. 15-22. Jahns, R.H., 1943, Sheet structure in granites, its origins and use as a measure of glacial erosion in New Eng land: Jour. Geology, v. 51, p. 71-98. Jenny, H., 1941, Factors of Soil Formation: New York, McGraw-Hill Book Co. Inc., 281 p. Jones, C.M., 1977, Effects of varying discharge regimes on bed-form sedimentary structures in modern rivers: Geology, v. 5, p. 567-570. Krammes, J.S., 1965, Seasonal debris movement from steep mountain slopes in southern California: U.S. Dept. Agriculture Misc. Publ. 970, p. 85-8 9. Ku, T.L., Bull, W.L., Freeman, S.T., and Knauss, K.G., 1979, Th230 - U234 dating of pedogenic carbonates in desert gravelly soils of Vidal Valley, southeastern California: Geol. Soc. America Bull., v. 90, p. 1063- 1073. Lamb, H.H. and Woodroffe, A., 1970, Atmospheric circulation during the last Ice Age: Quaternary Res., v. 1, p. 27-58. Langbein, W.B. and Schumm, S.A., 1958, Yield of sediment in relation to mean annual precipitation: Trans. Amer. Geophys. Union, v. 39, p. 1076-1084. Larsen, E.S., Jr., 1948, Batholith and associated rocks of Corona, Elsinore, and San Luis Rey Quadrangles, sou thern California: Geol. Soc. America Mem. 29, 182 p. Larsen, R.L., 1972, Bathmetry, magnetic anomalies and plate tectonic history of the mouth of the Gulf of Califor nia: Geol. Soc. America Bull., v. 73, p. 3345-3360. 2 2 1 Leighton and Associates, 1980, Review of 1980 storm damage along Santa Ana River bluffs, City of Norco, Califor nia: Prelim. Engineering Geology Rept., 14 p. Leonard, R.J., 1929, Polygonal cracking in granite: Am. J. Sci. , v. 18, p. 487-492. Leopold, L.B. , and Miller, J.P., 1954, A post-glacial chronology for some alluvial valleys in Wyoming: U.S. Geological Survey Water Supply Paper 1261, 90 p. _________, 1956, Ephemeral streams; hydraulic factors and their relation to drainage net: U.S. Geological Sur vey Prof. Paper 282-A, 37 p. Leopold, L.B., Wolman, M.G., and Miller, J.P., 1964, Flu vial processes in geomorphology: San Francisco, W.H. Freeman and Comp., Pub., 522 p. Lippincott, J.B., 1902, Development and application of water near San Bernardino, Colton and Riverside, California: U.S. Geological Survey Water Supply Paper 59, 141 p. Lofgren, B.E., 1971, Estimated subsidence in the Chino- Riverside and Bunker Hill-Yucaipa areas in southern California for a postulated water level lowering, 1965-20015: U.S. Geological Survey Water Resources Div., Open File Rept., 20 p. Louis, H., 1969, Singular and general features of valley deepening as resulting from tectonic or climatic causes: Z. Geomorph. N.F., v. 13, p. 472-480. Lynch, H.B., 1931, Rainfall and stream runnoff in southern California since 1769: Metropolitan Water Dist., S. Calif., Los Angeles, 39 p. MacKevett, E.M., 1951, Geology of the Jurupa Mountains, San Bernardino and Riverside Counties, California: California Div. Mines and Geology, Special Rept. no. 5, 14 p. Maxwell, J.C., 1960, Quantitative geomorphology of the San Dimas experimental forest, California: University of California, Los Angeles, Technical Rept. 19, 55 p. McLaren, P., 1981, An interpretation of grain size mea sures: Jour. Sed. Petrology, v. 51, p. 611-624. 222 McMurtry, G.M., and Fan, P.F., 1974, Clay and clay minerals of the Santa Ana River drainage basin, California: Jour. Sed. Petrology, v. 45, p. 1072-1078. Melton, F.A., 1940, A tentative classification of sand dunes; its application to dune history in the sou thern High Plains: Jour. Geol., v. 48, p. 205-227. Melton, M.A., 1958, Correlation structure of morphometric properties of drainage systems and their controlling agents: J. Geol., v. 66, p. 442-460. _________, 1960, Intravalley variation in slope angles re lated to microclimate and erosional environment: Bull. Geol. Soc. America, v. 71, p. 134-144. Mendenhall, W.C., 1905, The hydology of San Bernardino Valley, California: U.S. Geological Survey Water Supply Paper 142, 124 p. Miall, A.D., 1977, A review of the braided-river deposi- tional environment: Earth-Sci. Rev., v. 13, p. 1-62. Morton, D.M., 1975, Synopsis of the geology of the eastern San Gabriel Mountains, southern California: Califor nia Div. Mines and Geology Special Rept. 118, p. 170- 176. ______, 1978, Geologic map of the Fontana Quadrangle, San Bernardino and Riverside Counties, California: U.S. Geological Survey, Open File Rept., 78-19. Mulcahy, M.J., 1961, Soil distribution in relation to landscape development: Z. Geomorph., v . 5, p. 211- 225. Munz, P.A., 1968, Supplement to a California Flora: Berke ley, Univ. California Press, 224 p. Munz, P.A., and Keck, D.D., 1959, A California Flora: Berkeley, Univ. California Press, 16 81 p. Nardin, T.R. , 1981, Seismic stratigraphy of Santa Monica and San Pedro Basins, California Continental Border land; Late Neogene history of sedimentation and tec tonics (Ph.D. Thesis).:. Univ. of Southern California, 317 p. 223 Oberlander, T.H., 1974, Landscape inheritance and the pedi ment problem in the Mojave Desert of southern Califor nia: Am. J. Sci., v. 274, p. 849-875. Porter, S.C., 1971, Fluctuations in late Pleistocene alpine glaciations in western North America, in Turekian, K. K., (Ed.), The Late Cenozoic Glacial Ages: New Haven, Yale Univ. Press, p. 307-329. Raven, P.H., and Axelrod, D.I.,.1977, Origin and relation ships of the California flora: Univ. Calif. Publ. Botany, v. 72, 134 p. Rodgers, D.A., 1979, Vertical deformation, stress accumula tion, and secondary faulting in the vicinity of the Transverse Ranges of southern California: California Div. Mines and Geology Bull. 203, 74 p. Rogers, T.H., 1965, Geologic map of California, Santa Ana sheet: California Div. Mines and Geology, scale 1: 250,000. Royse, C.F., and Barsch, D., 1971, Terraces and pediment terraces in the southwest; An interpretation: Geol. Soc. America Bull., v. 78, p. 3177-3182. Ruxton, B.P., 1958, Weathering and surface erosion in granite at the piedmont angle, Balos, Sudan: Geol. Mag., v. 95, p. 353-377. Ruxton, B.P., and Berry, L., 1957, The weathering of .... granite and associated erosional features in Hong .. Kong: Geol. Soc. America Bull., v. 68, p. 1263-1292. Sabins, F.F., Jr., 1978, Remote sensing; principles and interpretation: San Francisco, W.H. Freeman and Co., 426 p. Santa Ana River Watermaster, 1976, Fifth annual report of the Santa Ana River Watermaster, 1974-1975: Orange Co. Water District Vs. City of Chino, et al., Case no. 117628, Orange Co., 90 p. _________, 1977, Sixth annual report of the Santa Ana River Watermaster, 1975-1976: Orange Co. Water District Vs. City of Chino, et al., Case no. 117628, Orange Co., 90 p. 224 ______ , 1981, Tenth annual report of the Santa Ana River Watermaster, 1979-1980: Orange Co., Water District Vs. City of Chino, et al., Case no. 117628, Orange Co., 90 p. Schumm, S.A., 1956, Evolution of drainage systems and slopes in badlands at Perth Amboy, New Jersey: Geol. Soc. America Bull., v. 67, p. 597-646. _________, 1968, Speculations concerning paleohydraulic controls ,of terrestrial sedimentation: Geol. Soc. America Bull., v. 79, p. 1572-1588. Schuyler, J.D., 1896-1897, Resevoirs for irrigation: U.S. Geological Survey 18th Ann. Rept., pt. 4, p. 617-740. Sharp, R.V., 1967, San Jacinto fault zone in the Peninsular Ranges of southern California: Geol. Soc. America Bull., v. 78, p. 705-730. _________, 1972a, Map showing recently active breaks along the San Jacinto fault zone between the San Bernardino area and Borrego Valley, California: U.S. Geological Survey Misc. Geol. Invest. Map 1-675. _________, 1972b, Pleistocene glaciation, Bridgeport Basin, California: Geol. Soc. America Bull., v. 83 p. 2233- 2260. _________, 1975, En echelon fault patterns of the San Jacin-. to fault zone: California Div. Mines and Geology, Spec. Rept. 118, p. 147-154. Sharp, R.V., Allen, C.R., and Meier, M.F., 1959, Pleisto cene glaciers of southern California mountains: Am. J. Sci., v. 257, p. 81-94. Sidler, W.A., 1968, Aqua Mansa and the flood of January 22, 1862, Santa Ana River: San Bernardino County Flood Control District, California, 10 p. Singer, J.A., and Price, M., 1971, Flood of January 1969 near Cucamonga, California: U.S. Geological Survey Hydrologic Investigations Atlas HA-425. Smith, H.T.U., 1965, Dune morphology and chronology in central and western Nebraska: Jour. Geol., v. 73, p. 557-578. 225] Smith, K.G., 1950, Standards for grading texture of ero- sional topography: Am. J. Sci., v. 248, p. 655-668. Soil Survey Staff, 1951, Soil Survey Manual: U.S. Dept. Agriculture Handbook 18, Washington D.C., U.S. Govt.. Printing Office, 503 p. , 1971, Soil Survey western Riverside Area, Calif ornia: U.S. Dept. Agriculture, Washington D.C., U.S. Govt. Printing Office, 157 p. _, 1980, Soil Survey of San Bernardino County, southwestern part, California: U.S. Dept. Agricul ture, Soil Conservation Service, Washington, D.C., U.S. Govt. Printing Office, 65 p. Strahler, A.N., 1952, Dynamic basis of geomorphology: Geol. Soc. America Bull., v. 63, p. 923-938. . ______, 1964, Quantitative geomorphology of drainage basins and channel networks: in Chow, V.T., (Ed.), Handbook of Applied Hydrology: New York, McGraw-Hill Publishers, 359 p. Stout, M.L., 1969, Radiocarbon dating of landslides in southern California and engineering applications: Geol. Soc. America Spec. Paper 123, p. 167-180. Thomas, H.E., 1962, The meteorologic phenomenum of drought in the Southwest: U.S. Geological Survey Prof. Paper 372-A, 50 p. Troxell, H.C., 1942, Floods of March 1938 in southern California: U.S. Geological Survey Water Supply Paper 844, 399 p. Troxell, H.C., Poland, J.F. , and others, 1951, Some aspects of the ground water supply in the South Coastal Basin California: U.S. Geological Survey Circ. 105, 10 p. Ursic, S.J., 1970, Hydrologic effects of prescribed burning and deadening upland hardwood woods in northern Mis souri: U.S. Forest Service Res. Paper, v. 54, p. 1—15. U.S. Dept. Commerce, 1969, Climatological data, California: U.S. Dept. Commerce, v. 73, p. 1-38. U.S. News and World Report, 1981a, America's 100 biggest cities: v. 90, p. 57-59. 226. . r-» * _________, 1981b, Tale of America's shrinking cities: v. 90, p. 66. U.S. Weather Bureau, 1964, Climatic summary of the United States, 1950-1960 with supplement for 1931-1952; Climatology of the United States, California: Wash ington, D.C., U.S. Government Printing Office no. 86-4, 165 p. Van Devender, T.R., 1977, Holocene woodlands in the south western deserts: Science, v. 198, p. 189-192. Vaughn, F.E., 1922, Geology of the San Bernardino Mountains north of San Gorgonio Pass (California): California Univ. Geol. Sci. Bull., v. 13, p. 319-411. Wahrhaftig, C., 1965, Stepped topography of the southern Sierra Nevada, California: Geol. Soc. America Bull., v. 76, p. 1165-1190. Weber, F.H., Jr., 1976, Preliminary map of faults in the Elsinore and Chino fault zones in northwestern River side County, showing accompanying features related to character and recency of movement: California Div. Mines and Geology Open File Rept., OFR.76-1-LA, 96 p. White, K.L., Jr., Pedogenic chronology of the Santa Ana River Terraces (Ph.D. Thesis): Univ. California Riverside, 155 p. Wolman, M.G., and Leopold, L.B., 1957, River flood plains: Some observations on their formation: U.S. Geological Survey Prof. Paper 282-C, p. 87-109. Woodburne, M.O., 1975, Cenozoic stratigraphy of the Trans verse Ranges and adjacent area, southern California: Geol. Soc. America Spec. Paper 162, 91 p. Woodford, A.O., Shelton, J.S., Doehing, D.O., and Morton, R.K., 1971, Pliocene-Pleistocene history of the Perris Block, southern California: Geol. Soc. America Bull., v. 82, p. 3421-3448. Yaalan, D.H., (Ed.), 1971, Paleopedology: origin, nature and dating of paleosols: Jerusalem, Israel Univ. Press, 370 p. 227 Yeats, R.S., 1978, Neogene acceleration of subsidence rates in southern California: Geology, v. 6, p. 456-460. _________, 1981, Quaternary flake tectonics of the Califor nia Transverse Ranges: Geology, v. 9, p. 16-20. Young, H.M., 1962, Statistical treatment of experimental data: New York, McGraw Hill Book Co.. Inc. , 172, p. 228 APPENDIX I. Tables 4-13: Nomenclature, climate, hydrology, vegetation, weathering criteria. TABLE 4. West coast strati graphic chart. M.Y. European Epochs North American Land Mammal Ages West Coast Benthonic Foraminiferal Stages 1 Pleistocene Rancholabrean Hal Han c 3 \Irvinqtonian Blancan 4 PIiocene Wheelerian 5 6 HemphiIlian Venturian 7 8 9 10 11 12 Upper Mi ocene Repetti an Delmontian Clarendonian Middle Mohnian 13 14 Luisian Miocene 15 Barstovian Relizian 16 17 Lower Miocene 18 19 20 Hemingfordian Saucesian 21 22 to to vb TABLE 5. Glacial chronology of California, North America and Europe. Epoch Series Glacial/Interglacial Stage European Alpine/No. Europe North America California Approximate Age Years B.P. Holocene Slight Glacial Interglacial Little Ice Age Xerothermic (Hypsithermal) Matthes Till Recess Peak Till Xerothermic (Hypsithermal) Present-10,000 Present-600 2000-4000 B.P. 8,000-5,000 Pleistocene 10,000-1.8 my Glacial Wurm/Weichselian Wisconsin 10,000-75,000 - I Tioga 17,000 Tahoe 70,000 Interglacial R:W/Eemian Sangamon 75,000-128,000 Glacial Type Riss/Saalian Illinoian .125-.195 my Interglacial NR* .195-.251 my Glacial Alt Riss/Saalian Illinoian Donner Lake Tills 0.25-0.39 my Interglacial Holsteinian NR 0.37-0.44 my Glacial Mindel/Lowestaft Till Illinoian Donner Lake Tills 0.44-0.5 my Interglacial Cromerian/? Yarmouth 0.5-0.75 my Glacial Gunz/Beeston Gl. Kansan Sherwin Till 0.75-0.9 my Interglacial D:G/Waalian Aftonian 0.9-1.3 my Glacial ? Donan/Eburonian Nebraskan McGee Till 1.3-1.6 my Pliocene 1.8-5 my *NR: Not recognized in North America 230 TABLE 6. Location of meterologic stations. Station Index # Latitude N. Longitude W. Elevation Years of Record Claremont Pomona College 1779 34 06 117 43 1196 61 Corona 2031 33 51 117 34 900 44 Fontana 3317W 34 06 117 26 1286 31 March A.F.B. 35 53 117 16 1538 Redlands 7306 34 03 117 11 1352 66 Riverside Fire Station 3 7470 33 57 117 24 820 72 San Bernardino Fire Station 5 7723 34 08 117 16 1125 82 Yorba Linda 9847 33 53 117 49 400 . 40 Data Source: U.S. Weather Bureau, 1964; NCAA. Monthly Synoptic Weather Reports. . Data presented in these tables summarizes data until 1952. have continued to report data until the present. This has unless where specific years are mentioned. All of these stations not been considered r ' t O l o o ' . M- TABLE 7. Climatic summary and comparison for for the record period 1934-1962. Riverside, Corona and San Bernardino Temperature Riverside Corona San Bernardino Mean Maximum Temperature of Warmest Month Mean Minimum Temperature of Warmest Month Mean Temperature of Warmest Month (July) (July) (July) 93.9 57.0 75.5 91.5 56.7 74.1 96.9 57.0 76.9 • Extreme High Temperature of Warmest Month (July) 118 116 116 Mean Maximum Temperature of Coldest Month Mean Minimum Temperature of Coldest Month Mean Temperature of Coldest Month (Jan.) (Jan.) (Jan.) 65.2 37.0 51.1 63.6 38.7 51.2 65.6 36.3 56.9 Extreme Low Temperature of Coldest Month (Jan.) 19 22 17 Mean Annual Temperature Range Mean Annual Temperature 24.4 62.9 22.9 62.7 26.0 63.4 Number of Months with Mean Monthly Temperature 50°F 12 12 12 Precipitation Mean Annual Rainfall Maximum Annual Rainfall (1941) Minimum Annual Rainfall (1947) Recent Maximum Rainfall (1980) 11.96 22.00 3.67 15.6 13.54 26.11. 2.40 22.24 17.5 35.45 5.95 26.57 Percent of Rainfall During the Winter h Year 85% 85% 85% Elevation 820' 900' 1094' to u> KJ TABLE 8. Longterm climatic monthly mean temperatures for selected valley stations on a transect west to east within the Upper Santa Ana Valley drainage.. Station Elevation Years of Record Jan. Feb. Mar. Apr. M ay Jun. Jul. Aug- Sep. Oct. Nov. Dec. Annual Yorba Linda 400' 1975 80 Avg 55.5 59.2 53.5 53.3 60.8 54.8 53.7 57.8 56.9 54.1 62.0 60.0 61.8 61.0 63.3 65.6 68.1 67.5 72.0 75.0 72.3 70.4 74.9 72.7 72.5 70.9 70.5 64.5 69.7 65.7 59.6 63.0 60.8 55.8 60.6 55.4 66.1 64.3 62.5 Corona 900' 1975 80 Avg 54.3 56.4 51.6 52.3 59.0 53.3 54.2 56.5 51.9 54.3 60.8 57.1 63.8 61.8 62.2 67.4 67.3 69.4 74.0 77.1 74.9 72.8 75.6 74.9 73.8 70.8 71.9 64.3 67.2 65.3 57.9 59.2 59.0 54.5 58.3 47.9 62.0 64.2 62.4 Claremont 1196' 1975 80 Avg 57.5 54.4 51.0 50.5 57.5 52.5 54.2 54.4 54.5 51.3 60.8 57.8 61.5 58.7 61.5 65.3 67.6 67.8 73.8* 77.3* 73.1 73.6 75.7 73.6 73.7 69.3 70.8 63.1 67.2 64.4 57.8 58.9 58.4 54.0 56.9 52.2 61.3 63.2 61.5 Fontana 1286’ 1975 80 A vg 59.6 56.1 51.2 54.8 58.1 53.1 56.0 54.6 55.7 55.6 60.3 59.1 64.9 60.4 63.7 69.7 69.4 69.0 76.4 78.8 75.4 76.4 76.7 75.4 77.8 72.3 71.4 68.0 69.1 65.1 62.6 59.9 58.9 60.0 59.0 52.2 65.2 64.6 61.8 Riverside 820' 1975 80 Avg 54.0 57.3 51.5 53.8 59.7 53.2 55.6 57.3 56.3 56.3 63.4 60.4 65.8 63.6 64.6 69.5 72.5 69.6 76.6 83.3 75.7 75.5 78.4 75.6 75.6 74.1 71.3 64.7 68.6 65.3 58.2 59.6 58.2 55.0 57.9 52.9 63.4 66.3 61.9 S an Bernardino 1125' 1975 80 A vg 55.1 57.4 51.3 54.5 57.4 53.4 55.2 59.9 56.2 55.2 56.5 60.3 66.3 63.7 64.6 69.8 63.0 70.1 78.5 82.6 76.5 N.D. 79.4 76.5 77.2 75.9 72.8 66.1 71.0 65.4 58.9 62.4 58.1 56.3 60.0 52.7 63.0 65.8 63.4 Redlands 1352' 1975 80 A vg 53.4 55.0 50.5 52.5 N.D. 52.3 53.2 55.3 55.5 54.0 61.8. 59.7 64.0 61.5 64.1 58.3 70.9 70.1 77.4 79.7 76.5 N.D. 76.4 76.3 75.4 71.7 72.4 64.1 67.4 65.1 57.9 58.7 57.9 54.3 56.4 52.7 61.3 65.0 62.4 March A F B 1538' 1975 80 53.0 53.8 47.7 59.0 50.7 50.7 62.4 55.1 62.5 60.0 66.2 69.5 77.2 79.7 73.2 76.0 74.7 72.1 63.4 71.6 56.5 60.9 50.3 59.6 61.5 64.0 Avg — — — — — — — — — — — — — Data Source: N O A A Monthly Synoptic Weather Reports 233 TABLE 9. Longterm climatic monthly precipitation means for selected valley sta tions on a transect west to east within the Upper Santa Ana Valley drainage. This data compares monthly means for a wet year, 1980, and a dry year, 1975, with longterm climatic means. Years of Station Elevation Record Jan. Feb. Mar. A pr.:. Yorba Linda 400' 1975 80 Avg 0.23 8.87 2.72 2.61 11.69 3.14 3.95 4.70 2.45 1.80 0.41 1.15 Corona 900' 1975 80 Avg 0.26 6.25 2.75 1.24 9.98 2.81 2.87 4.06 2.09 1.47 1.37 0.99 Claremont 1125' 1975 80 Avg 0.27* 11.41 3.62 2.90 16.46 3.60 5.18 4.80 3.43 1.58 0.29 1.41 Fontana 1286' 1975 80 Avg 0.16 10.33 3.40 1.85 13.52 4.31 4.21 5.44 3.12 0.84 0.41 1.73 Riverside 820' 1975 80 A vg 0.12 5.47 1.98 1.16 6.31 2.28 2.67 3.54 2.07 1.14 0.07 0.87 S an Bernardino 1125' 1975 80 Avg 0.35 8.96 3.11 2.67 9.88 3.55 4.33 5.47 2.89 1.81 0.94 1.52 Redlands 1352' 1975 80 Avg 0.43 7.73 2.43 1.32 9.90 2.84 3.52 3.89 2.57 1.56 1.20 1.26 March A F B 1538' 1975 80 Avg 0.25 5.19 1.26 8.09 2.58 2.16 1.37 0.41 Data Source: N O A A Monthly Synoptic Weather Reports March A F B Weather Report *Rancho Santa A na Botanic Garden Record M ay Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual 0.05 0.25 0.39 0.00 0.00 0.04 0.00 0.00 0.01 0.00 0.00 0.05 0.00 0.00 0.31 0.36 0.00 0.69 0.41 0.00 1.11 0.30 0.72 2.89 9.71 26.64 14.95 0.00 0.12 0.30 0.00 0.00 0.50 0.00 0.00 0.01 0.00 0.00 0.06 0.00 0.00 0120 0.03 0.00 0.70 0.40 0.00 0.85 0.33 0.46 2.61 5.50 22.24 13.39 0.24 0.62 0.51 0.10 0.03 0.09 0.00 0.00 0.01 0.00 0.00 0.09 0.00 0.00 0.26 0.28 0.13 0.88 0.13 0.00 1.38 0.36 0.74 3.17 11.04 34.48 18.45 0.00 0.24 1.48 0.00 0.00 0.08 0.00 0.00 0.01 0.00 0.00 0.14 0.00 0.00 0.28 0.94 0.00 1.11 0.45 0.00 1.06 0.31 0.69 3.68 8.76 30.63 19.56 0.04 0.00 0.32 0.03 0.00 0.04 0.00 0.00 0.02 0.00 0.00 0.17 0.05 0.00 0.16 0.18 0.00 0.60 0.46 0.00 0.79 0.76 0.19 2.15 6.58 15.60 11.42 0.22 0.04 0.49 0.23 0.00 0.10 0.00 0.00 0.04 0.00 0.00 0.17 0.00 0.00 0.21 1.17 0.70 0.84 0.74 0.00 1.35 0.58 0.58 3.26 11.59 26.57 17.50 0.15 0.46 0.52 0.00 0.05 0.11 0.00 0.00 0.04 0.00 0.00 0.22 0.00 0.00 0.32 0.43 0.06 0.85 0.73 0.00 1.08 0.45 0.00 2.55 6.76 22.99 14.76 0.00 0.11 0.00 0.00 0.26 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.33 0.00 0.35 0.17 6.40 16.13 — — — — — — — — 9.65 to C O TABLE 10. Longterm climatic means for selected valley stations with the record for 1941, a wet year, and 1947, a dry year, precipitation records in cluded. Station Elevation Element Jan. Feb. Mar. Apr. M ay Jun. Jul. Aug. Sep. Oct. Nov. Dec. Annual Yorba Linda 400' T 53.5 54.8 56.9 60.0 63.3 67.5 72.3 72.7 70.5 65.7 60.8 55.4 62.5 P 2.72 3.14 2.45 1.15 0.39 0.04 0.01 0.05 0.31 0.59 1.11 2.89 14.95 P 4 1 2.48 8.78 11.58 4.99 .63 .00 .00 .02 .00 2.21 .30 4.87 34.86 P 47 .34 .27 .98 .06 .62 .02 .00 .05 .05 .02 .04 1.17 3.62 Corona 900' T 51.6 53.3 51.9 57.1 62.2 69.4 74.9 74.9 71.9 65.3 59.0 47.9 62.4 P 2.75 2.81 2.09 .99 .30 .50 .01 .06 .20 .70 .85 2.61 13.39 P 4 1 1.81 6.32 7.72 3.40 .85 .00 .00 .00 .00 2.54 .88 3.09 26.11 P 47 .33 .13 .68 .18 .00 .04 .00 .02 .00 .00 .00 1.02 2.40 Claremont 1125' T 51.0 52.5 54.5 57.8 61.5 67.8 73.1 73.6 70.8 64.4 58.4 52.2 61.5 P 3.62 3.6 3.43 1.41 .51 .09 .01 .09 .26 .88 1.38 3.17 18.45 P 4 1 2.57 9.32 12.54 3.86 .03 • .04 .00 .00 .00 1.51 0.44 4.62 34.93 P 47 .76 .32 1.12 .41 .20 .03 .00 .04 .06 .01 .16 2.13 5.24 Fontana 1286' T 51.2 53.1 55.7 59.1 63.7 69.0 75.4 75.4 71.4 65.1 58.9 52.2 61.8 P 3.4 4.31 3.12 1.73 1.48 .08 .01 .14 .28 1.11 1.06 3.68 19.56 P 4 1 3.93 7.00 8.11 3.10 1.24 .00 .00 .30 .00 2.47 .43 4.94 31.52 P 47 N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. Redlands 1352' T 50.5 52.3 55.5 59.7 64.1 70.1 76.5 76.3 72.4 65.1 57.9 52.7 62.4 P 2.43 2.84 2.57 1.26 .52 .11 .04 .22 .32 .85 1.08 2.25 14.76 P 4 1 1.33 4.51 7.46 2.95 2.27 .04 .00 .70 .00 2.52 .50 3.85 24.13 P 47 .21 .99 1.12 .83 .14 .00 .00 .05 .18 .03 .04 1.67 5.26 Riverside 820' T 51.5 53.2 56.3 60:4 64.6 69.6 75.7 75.6 71.3 65.3 58.2 52.9 61.9 P 1.98 2.28 2.07 .87 .32 .04 .02 .17 .16 .60 .79 2.15 11.42 P 4 1 1.22 4.81 5.96 2.78 .94 .05 .00 .30 .00 2.21 .51 3.22 22.00 P 47 .12 .36 .91 .25 .05 .05 .00 .00 .03 .09 .03 1.78 3.67 S an Bernardino 1125' T 51.3 53.4 56.2 60.3 64.6 70.1 76.5 76.5 72.8 65.4 58.1 52.7 63.4 P 3.11 3.55 2.89 1.52 .49 .10 .04 .17 .21 .84 1.35 3.26 17.5 P 4 1 2.57 9.05 9.65 3.82 .25 .38 .00 .54 .00 2.61 .70 5.88 35.45 P 47 .50 1.02 1.11 .91 .33 .13 .00 .00 .26 .09 .00 1.60 5.95 Data Source: U.S. Weather Bureau, 1964 235 TABLE 11. Comparison of Discharge regimes pre-1900 and present day. Location Riverside Narrows Year 1888 1889 1890 1891 1975 1976 Discharge in cfs July August September 10.10 26.52 21.36 8.51 11.00 18.76 25.26 20.39 9.48 11.20 15.50 26.00 129.47* Yearly rainfall in inches 17.76 20.97 25.45 18.08 11.12 15.86 Average rainfall San Bernardino 17.5 Note* The high flow in September 1976 reflects storm flood and rapid street run-off after a tropical storm "dumped" 5.12 inches of rain in San Bernardino, September 9-10, 1976. Data Source: Lippincott, 1902, U.S. Geological Water Supply Paper 59 1974 - 1975 Sixth Annual Report, Santa Ana Watermaster 1975 - 1976 Seventh Annual Report, Santa Ana Watermaster to "C T i 23 7 TABLE 12. Species lists for dominant members of the plant communities found on the northern Perris Block and Santa Ana River floodplain. A. COASTAL SAGE SCRUB (Soft Chaparral) Artemisia oalifomioa Compositae Coast Sagebrush Brodiaea pulchella Amaryllidaceae Blue Dicks Cupressus sp. Cupressaceae Cyprus sp. Encelia oalifomioa Compositae Brittle Bush Enoelia farinosa Compositae Desert Encelia Eriodictyon triohooalyx Hydrophyllaceae Smoothleaf Yerba Santa Eriogonom fasciculatum Polygonaceae Wild Buckwheat Haploppapus venetus Compositae Goldenbush Iscmeris aTborea Caparidaceae Bladderpod Niootiana glauca Colonaceae Tree Tobacco Opuntia oooidentalis Cactaceae Prickly Pear Cactus Opuntia parryi Cactaceae Valley Choila Ribes aureum Saxifragaceae Western Golden Currant Rhus laurina Anacardiaceae Laurel Sumac Salvia apiana Labiatae White Sage Salvia leuoophylla Labiatae Salvia mellifera Labiatae Black Sage Toxicodendron diversiloba Anacardiaceae Poison Oak Trichostema lanoeolatum Labiatae Vinegar Weed B. VALLEY GRASSLAND Aristida sp. Gramineae Three-Awn Avena sp. Gramineae Wild Oats Brassioa nigra Brassicaceae Mustard Bromus sp. Gramineae Brome Grass (Chess) Cirsiwn sp. Compositae Thistle Erodium oicutarium Geraniaceae Storksbill Belianthus annuus Compositae Sunflower Hordeum sp. Gramineae Wild Barley (Foxtail) Boa sp. Gramineae Bunch Grass Salsola kali var tenuifolia Chenopodiaceae Russian Thistle Sorghum halepense Gramineae Johnson Grass Stipa sp. Gramineae Needle Grass Taraxacum officinate Compositae Dandelion C. RIPARIAN WOODLAND AND FLOODPLAIN SANTA ANA RIVER * Floodplain (Level I) Arundo donax Gramineae Giant Reed Bidens laevis Compositae Bur-marigold Distichlis spioata var stricta Gramineae Salt Grass Juncus sp. Gramineae Wire Grass Melilotus albus Leguminosae Sweet Clover Nasturtium officinale Cruciferae Water Cress Populus fremontii Salicaceae Cottonwood Fremont Salix sp. Salicaceae Willow Typha latifolia Typhaceae Cat-Tails Veronica anagallis aquatioa Scrophulariaceae Speedwell 238: Sandflats (Level II) Arundo donax Gramineae Giant Reed Baaaharis viminae Compositae Mule Fat B-Cdens laevis Compositae Bur-marigold Eohinoohloa crusgalli Gramineae * Populus fremontii Salicaceae Fremont Cottonwood Salix hindsiana Salicaceae Sandbar Willow Salix lasiolepis Salicaceae Arroyo Willow Typhan lati folia Typhaceae Cat-Tails Terrace T10 (3-4 feet above floodplain) Atriplex semibaooata Chenopodiaceae Australian Saltbush Baaaharis emoryi Compositae Baaaharis viminae Compositae Mule Fat Distichlis spiaata var striata Gramineae Salt Grass Niaotiana glauca Solonaceae Tree Tobacco Populus fremontii Salicaceae Fremont Cottonwood Rosa oalifomioa Rosaceae Wild California Rose Rubus vitifolius Rosaceae California Blackberry Salix hindsiana Salicaceae Sandbar Willow Salix lasiolepis Salicaceae Arroyo Willow Sambuaus mexiaana Caprifoliaceae Elderberry Vitis girdiana Vitaceae Wild Grape Dunes Arundo donax Gramineae Giant Reed Brcmus sp. Gramineae Brome Grass Erodium oioutarium Geraniaceae Storksbill Salix hindsiana Salicaceae Sandbar Willow Baaaharis viminae Compositae Mule Fat Terrace T9 (8-10 feet) Amaranthus albus Amaranthaceae Tumbleweed Artemisia califomicus Compositae Coast Sagebrush Brcmus sp. Gramineae Brome Grass (Chess) Croton aalif'omicus Euphorbiaceae Croton distichlis spiaata stricta Gramineae Salt Grass Erodium oioutarium Geraniaceae Storksbill Eriogonum fasciculatum Polygonaceae Wild Buckwheat Hordeum Gramineae Wild Barley (Foxtail) Niaotiana glauca Solonaceae Tree Tobacco Salsola kali var tenuifolia Chenopodiaceae Russian Thistle Sambuaus mexiaana Caprifoliaceae Elderberry Toxicodendron diversiloba Anacardiaceae Poison Oak TABLE 13. Granite Weathering Table, Field Weathering Criteria 1. Change in rock color from that of the unweathered condition 2. Mechanical strength of rock (how easily it can be broken manually) 3. Ease with which roots penetrate the rock matrix or fractures 4. How distinctly original jointing is preserved 5. The sound a rock hammer makes when striking the rock 6. Whether or not the rock is spalling (crumbling) 7. Whether or not the rock is plastic in nature when wet. Field Weathering Classes Class 1, Unweathered Rock.— Unweathered rock will ring from a hammer blow; cannot be dug by the point of a rock hammer; joint sets are the only visible frac tures; no iron stains emanate from biotites; joint sets are distinct and angular; biotites are black and compact; feldspars appear to be clear and fresh. Class 2, Very Weakly Weathered Rock.— Very weakly wea thered rock is similar to class 1, except for visible iron stains that emanate from biotites; biotites may also appear to be "expanded" when viewed through a hand lens; feldspars may show some opacity; joint sets are distinct and angular. Class 3, Weakly Weathered Rock.— Weakly weathered rock gives a dull ring from a hammer blow; can be broken with moderate difficulty into "hand-sized" rocks by a hammer; feldspars are opaque and milky; no root penetration; joint sets are subangular. Class 4, Moderately Weathered Rock.— Moderately wea thered rock may be weakly spalling. Except for the spall rind, if present, rock cannot be broken by hand; no ring from hammer blow; feldspars are opaque and milky; biotites usually have a golden yellow sheen; joint sets are indistinct and rounded to sub- angular. Class 5, Moderately Well Weathered Rock.— Moderately well weathered rock will break into small fragments or sheets under moderate pressure from bare hands; usually spalling; root penetration is limited to fractures, unlike class 6 rock where roots penetrate through the rock matrix; joint sets are weakly visible and rounded; feldspars are powdery; biotites have a light-golden sheen. Class 6, Well-weathered Rock.— Well-weathered rock can be broken into sand-sized particles (grus); usually it is so weathered that it is difficult to determine whether or not the rock is spalling; roots can pene trate between grains; only major joints are preserved and filled with grus; feldspars are powdery; biotites may appear as thin silver or white flakes. Class 7, Very Well Weathered Rock.— Very well weathered rock has feldspars that have weathered to clay min erals; rock is plastic when wet; no resistance to roots. Field weathering guide and classes were established by Clayton and Arnold (1972) . 239 240 APPENDIX II. Tables 14-20: Drainage morphology. TABLE 14. Comparison of main drainage basin morphologic characteristics. Mockinqbird Piqeon Pass Sycamore Relative relief H 1780 ft. 2300 ft. 2600 ft. h 840 ft. 805 ft. 710 ft. Drainage density D6 16.34 miles/sq. mile 16.48 miles/sq. mile 15.01 miles/sq. mile Relief ratio *h .018 .049 .035 Basin area A6 11.15 sq. miles 3.65 sq. miles 10.05 sq. miles Total stream length < h. ) 6 182.2 miles 60.16 miles 150.85 miles Number of streams (IN) 1508 527 1185 Bifurcation ratio *b 4.37 3.23 3.79 Stream Frequency F S 135.24 144.11 117.91 Length orders 1 . .10 miles .07 miles .08 miles 2 .13 miles .15 miles .18 miles 3 .20 miles .32 miles .28 miles 4 .36 miles .61 miles .57 miles 5 1.88 miles .25 miles .58 miles 6 5.84 miles 5.84 miles 9.35 miles Mean length index rl 1.99 2.29 2.22 241 TABLE 15. Comparison of all north-facing drainage basins. Mean Values Range of values for north facing slopes 3 and 4 Relative relief H h 1600 - 2220 feet 1070 - 1570 feet Drainage density D4 19.72 miles/sq. miles 15.81 - 23.33 miles/sq. miles Relief ratio Rh .091 0.27 - .239 Basin area A4 0.28 sq. miles 0.18 - 0.45 sq. miles Total stream length <sl)4 5.65 miles 8.6 - 8.88 miles Number of streams <«04 53 37 - 88 Bifurcation ratio *b 3.10 2.62 - 3.59 Stream frequency Fs 174.07 91.67 - 250.00 Stream length ratio 1.79 1.54 - 2.08 Length orders 1 0.08 miles 0.07 - 0.10 miles 2 0.13 miles 0.10 - 0.17 miles 3 0.27 miles 0.18 - 0.38 miles 4 0.44 miles 0.20 - 0.70 miles to NJ TABLE 16. Comparison of all south-facing drainage basins. Mean Values Relative relief Drainage density Relief ratio Basin area Total stream length Number of streams Bifurcation ratio Stream frequency Stream length ratio Length orders H h D4 Rh A4 <EL)4 (EN)„ 23.20 miles/sq. miles .082 0.27 sq. miles 8.05 miles 36 2.62 176.92 1.50 0.11 miles 0.23 miles 0.25 miles 0.4 miles Range of values for south facing slopes 1 and 2 1700 - 2040 feet 1180 - 1535 feet 14.13 - 27.27 miles/sq. miles .163 - .032 0.11 - 0.82 sq. miles 3.0 - 11.59 miles 26 - 52 2.49 - 2.78 52.44 - 288.89 1.19 - 1.78 0.07 - 0.17 miles 0.11 - 0.42 miles 0.14 - 0.40 miles 0.14 - 1.10 miles £VZ TABLE 17. Comparison with other southern California watersheds. 244 Drainage Basin San Gabriel Mountains •Bell •Bailey •Wolfskill ••Bailey *‘Bradbury ••Santa Anita (Lwr) *‘Sierra Madre *‘Eaton Wash **Wolfskill ••Bell ‘•Volfe Verdugo Hills •‘•Sunland ‘•‘Altadena •**La Crescenta Basin Stream Stream Stream Area A Length Density Area Length Sq. ml. L ml. L/A Sq. km. km. L/A 12.98 3.5 28 8. 00 11.42 1.55 11 7.09 11.32 6.4 45 7.03 20.38 1.5 19 12.66 24.62 1.7 26 15.29 18.22 4.15 47 11.32 21.85 6.3 85.5 13.57 16.72 21.00 218 10.38 18.12 6.4 72 11. 25 23.00 3.5 50 14.28 24.15 3.0 45 15.00 .049 1.70 34.50 21.44 .050 . 85 17.00 10.56 .118 2.28 19. 20 11.93 .088 1.77 22. 10 13.73 .119 22.01 15.90 10.51 . 056 1. 18 21. 10 13.11 .027 .53 19.70 12.24 .032 .93 29.30 18.20 .80 1.34 16.70 10.37 .128 2.30 17.80 11.06 .181 2.74 15.20 9.44 . 060 .98 16.40 10.19 .050 .85 17. 10 10.62 .086 1.40 16.30 10.12 .094 1.47 15.60 9.69 .045 .68 15.20 9.44 .079 1.50 18.90 11.74 .205 4.12 20.20 12.55 . 244 4. 10 16.80 10.44 .319 5.53 17.40 10.81 .139 2.22 16.00 9.94 .063 1.19 18. 90 11.74 PERRIS BLOCK Mockingbird A So F 1 B So F 2 C No F 3 D No F 4 Pigeon Pass A So F 5 B So F 6 C No F 7 D No F Sycamore 8 A So F 9 B So F 10 C No F 11 D No F 12 Data obtained from: •Bauer, 1980 “ Maxwell, 1960 •••Smith, 1950 11.15 182.2 16.34 27.88 293.34 10.52 0.23 4.24 18.42 .58 6.82 11.76 .18 4.68 26.0 .46 7.54 16.39 .36 6.76 18.78 .92 10.88 11.83 .18 3.8 21.0 .46 6.13 13.33 3.65 60.16 16.48 9.13 96.85 10.61 0.11 3.0 27.27 0.27 4.83 17.89 0.18 4.2 2 3.33 0.46 6.76 14 .70 0.18 3.6 20.00 0.46 5.8 12.61 10.05 150.85 15.01 25.13 242.87 9.67 1. 82 11.59 14.13 2.08 18.76 9.02 . 18 4.8 26 .66 0.46 7.73 16.80 .42 6. 64 15.81 1.09 10.69 9.81 .46 8. 88 19. 30 1.18 14.29 12.11 So F - South facing drainage basin Ho F - North facing basin Data has been converted to show all drainage density as function of L/A using both miles and kilometer measurements to allow com. parison of results. TABLE 18. Drainage basin analysis for Pigeon Pass. Main S. A. Facing (5) B. S. Facinq (6) N. c- Facing (7) D. N. Facing (8) Relative relief H 2300 1700 2040 2220 2160 h 805 1240 1180 1210 1070 Drainage density D 16.48 27.27 26.67 23.33 20.00 Relief ratio Rh .045 .145 .163 .239 .191 Basin area A 3.65 .11 .12 .18 .18 Total stream length L 60.16 3.0 -- 4.2 3.6 Number of streams N 527 30 _______ 46 38 Bifurcation ratio Rb 3.23 2.78 _______ 3.32 3.08 Stream frequency Fs Length orders 1 .07 .08 .09 .07 .07 2 .15 .11 .14 .11 .10 3 .32 .20 .68 .38 .18 4 C .61 .25 5.84 .20 ------------ .20 .64 3 6 ------------ ------------ — _ ------------ Mean length index rl 1.99 1.38 1.56 2.08 fo UT TABLE 19. Drainage basin analysis for Sycamore/Tequesquito Canyon. Main A. South Facing (9) B. South Facinq (10) C. North Facinq (11) D. North Facinq (12) Relative relief H 2600 1900 1660 1750 1620 h 710 1535 1260 1530 1440 Drainage density D 15.01 14.13 26.67 15.81 19.30 Relief ratio Rh .035 .032 .086 .027 .045 Basin area A 10.05 0.82 0.18 0.42 0.46 Total stream length EL 150.85 11.59 4.8 6.64 8.88 Number of streams EN 1185 43 52 56 88 Bifurcation ratio Rb 3.79 2.49 2.53 2.62 3.19 Stream frequency Fs Length orders 1 .08 .17 .07 .08 .07 2 .18 .32 .13 .12 .17 3 .38 .40 .14 .18 .28 4 .57 1.10 .14 .70 .24 5 .58 -- -- -- -- 6 9.35 -- -- -- -- Mean length index rl 2.22 1.78 1.26 2.00 1.54 to oV TABLE 20. Drainage basin analysis for Mockingbird Canyon. Main A. S. Facinq (1) B. S. Facing (2) c. N. Facinq (3) D. N. Facinc Relative relief H 1780 1760 1800 1780 1600 h 840 1530 1420 1570 1190 Drainage density D 16.34 18.43 26.00 18.78 21.11 Relief ratio Rh .018 .039 .056 '.0414 .088 Basin area A 11.15 0.23 0.18 0.36 0.18 Total stream length IL 182.2 4.24 4.68 6.76 3.8 Number of streams IN 1508 29 26 55 37 Bifurcation ratio Rb 4.37 2.73 2.59 3.59 2.90 Stream frequency Fs Length orders 1 .10 .12 .12 .10 .07 2 .13 .17 .42 .16 .11 3 .20 .32 .20 .38 .23 4 .36 .28 .28 .36 .52 5 1.88 -- -- --- -- 6 5.84 -- -- -- -- Mean length index rl 2.29 1.38 1.19 1.61 1.97 to i t * . •o 248 APPENDIX III. Soil Pedon Descriptions. 2 49 Pedon Number: A Fallbrook Series Location: Riverside Co., C a., roadside cu t, Canyon Crest Road, R iverside, elevation 492 fe e t (755 m), southeast corner of sec. 6 , T .3 S ., R.4W. Physiography: Paloma Surface, near crest of ridge. C la s s ific a tio n : Loamy, mixed, thermic, Typic Haploxeralfs. A1 0-11" (0-28 cm)—Yellowish brown (10YR 5/4) sandy loam, dark brown (10YR 3/3) moist*, weak, medium and fin e granular structure; s o ft, very fr ia b le , nonsticky and nonplastic; many fin e and very fine roots; many fin e and very fine irre g u la r pores; neutral (pH 7 .0 ); c le a r, abrupt boundary. (3 to 14 inches [8 to 35 cm] thick) A12 11-22" (28-55 cm)--Brown (10YR 5 /3 ) sandy loam, dark brown (10YR 3/3) moist; massive, s lig h tly hard, very fr ia b le , nonsticky and nonplastic; com m on fin e and very fin e roots; many, fin e and very fin e , irre g u la r f ores; neutral (pH 7 .0 ); c le a r, smooth boundary. (6 to 12 inches 15 to 30 cm] thick) B2t 22-39" (55-98 cm)--Reddish brown (5YR 4 /4 ) sandy loam, dark reddish brown (5YR 3/4) moist; strong, coarse, subangular blocky structure; very hard, very firm , very sticky and p la s tic ; com m on fine and very fin e roots; many, fin e , irre g u la r pores; common, moderately thick clay film s on ped faces; neutral (pH 7 .0 ); gradual, clear boundary. (10 to 20 inches [25 to 50 cm] thick) B3t 39-53" (98-133 cm)--Reddish brown (5YR 4 /4 ) sandy clay loam, dark reddish brown (5YR 3/4) moist; strong, coarse, subangular blocky structure; very hard, very firm , very sticky and p la s tic , many fin e roots; common, fin e irre g u la r pores; com m on thin clay film s on ped faces; many angular quartz and feldspar fragments; neutral (pH 7 .0 ); gradual, irre g u la r boundary. (15 to 25 inches [38 to 63 cm] thick) C 53" (133 cm)— Weathered granodiorite. This becomes harder with depth but where exposed forms a crumbly g ran itic grus. 250 Pedon Number: B Fall brook Series Location : Riverside Co., Ca., north-facing roadside cut, Box Springs Canyon Surface, Canyon Crest Road, elevation 1360 fe e t (415 m), northeast corner of sec. 7, T .3 S ., R.4W. Physiography: Gently sloping surface, buried fossil soil indicates at least two periods of i n f i l l . * C lassification: Loamy, mixed, therm ic, Typic Haploxeralfs over a buried D urixeralfs. A1 0-7" (1-18 cm)--Brown (10YR 5 /3 ) sandy loam, dark brown (10YR 3/3) moist; weak, medium and fin e granular structure; loose, very fr ia b le , nonsticky and nonplastic; many fin e and very fin e roots; many fin e , irre g u la r pores; neutral (pH 6 .6 ); c le a r, smooth boundary. (3 to 8 inches [8 to 26 cm] thick) A12 7.-14" (18-36 cm)--Brown (10YR 5/3) sandy loam, dark brown (10YR 3/3) moist; massive, s lig h tly hard, very fr ia b le , nonsticky and non p la s tic ; com m on fine and very fin e roots; many, fin e and very fin e , irre g u la r pores; neutral (pH 7 .0 ); c le a r, smooth boundary. (5 to 10 inches [12 to 25 cm] th ick) B2t 14-26" (36-66 cm)--Reddish brown (5YR 4 /4 ) sandy clay loam, dark reddish brown (5YR 3/3) moist; strong, coarse, medium and fin e , subangular blocky structure; hard, very firm , sticky and p la s tic ; com m on fin e and very fin e roots; many, fin e , and very fin e , irre g u la r pores; neutral (pH 7 .0 ); c le a r, smooth boundary. (10 to 16 inches [25to 40 cm] th ick) B3t 26-41" (63-104 cm)—Reddish brown (5YR 4 /3 ) sandy clay loam, dark brown (7.5YR 4 /4 ) moist; moderate, medium and fin e , angular blocky structure; hard, firm s lig h tly sticky and s lig h tly p la s tic ; com m on fin e and very fine roots; many, fin e and very fin e irreg u lar pores; neutral (pH 7 .0 ); gradual, smooth boundary. (15 to 20 inches [38 to 56 cm] th ick) IIB2tb 41-53" (104-135 cm)— Reddish brown (4YR 4 /3 ) sandy clay loam, dark reddish brown (5YR 3/4) moist; strong, angular coarse, medium and fin e angular blocky structure; hard, firm , sticky and p lastic; few fin e roots; common, fin e , irre g u la r pores; very few, thin clay film s; neutral (pH 7 .0 ); c le a r, smooth boundary. (10 to 15 inches [25 to 32 cm] th ick) IIB22tb 53-67" (135-145 cm)—Dark reddish brown (2.5YR 3 /4 ) clay loam, dark reddish brown (5YR 3/4) moist; strong, medium and fin e , angular blocky structure; hard, firm , sticky and p la s tic ; few fine roots; few, fin e irre g u la r pores; common, moderately thick clay film s on ped faces and in pores; neutral (pH 7 .0 ); abrupt, smooth boundary. (10 to 18 inches [25 to 45 cm] th ick) IIC s1b 67-74" (170-188 cm)--Strong brown (7.5YR 5/6) loam, dark brown (7.5YR 4 /4 ) moist; massive, coarse polygonal structure on upper surface, 40 percent forms durinodes; extremely hard, firm , s lig h tly sticky and p la s tic ; m ildly alkalin e (7.6 pH); s lig h tly effervescent; fin e film s of calciun carbonate. 251 Pedon Number: C Location: Riverside Co., Ca., gully cu tting , 50 yards (46 m) east of La Sierra Avenue, elevation 1300 fe e t (377 m), southwest quarter corner of sec. 32, T .1 S ., R.5W. Physiography: Mid-Pleistocene Jurupa Surface (T2). This surface now abandoned and soils are r e lic ts . AI 0-8" (0-20 cm)— Reddish yellow (7.5YR 5 /5 ) sandy loam, dark reddish brown (5YR 5 /4 ) moist; moderate, fine granular and subangular blocky structure; s lig h tly hard, s lig h tly sticky and s lig h tly p la s tic ; few fin e roots; few fin e irre g u la r pores; s lig h tly acid (pH 6 .5 ); c le a r, smooth boundary. (6 to 11 inches [15 to 28 cm] th ick) BI 8-16" (20-40 cm)--Reddish brown (5YR 5 /4 ) loam, reddish brown (5YR 4 /3 ) moist; moderate, medium, angular blocky structure; hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; few fin e roots; few fin e tubular pores; s lig h tly acid (pH 6 .5 ); gradual, smooth boundary. (7 to 12 inches [18 to 40 cm] thick) B21t 16-30" (40-75 cm)--Reddish brown (5YR 4 /4 ) sandy, clay loam; dark reddish brown (5YR 3/3) moist; moderate, coarse blocky structure; very hard, firm , sticky and p la s tic ; few, fin e roots; few, fin e , tubular pores; many, moderately thick clay film s on ped surfaces and in pores, s lig h tly acid (pH 6 .5 ); gradual, smooth boundary. (10 to 15 inches [25 to 38 cm] th ick) B3 30-39" (75-98 cm)--Yellowish red (5YR 5 /6 ) sandy clay loam, reddish brown (5YR 4 /4 ) moist; moderate, coarse angular blocky structure; very hard, firm , sticky and p la s tic ; common, thin clay film s on ped surfaces; s lig h tly acid (pH 6 .5 ); c le a r, smooth boundary. (8 to 10 inches [20 to 25 cm] thick) C 39-54" (98-135 cm)--Yellowish brown (10YR 5 /6 ) sandy loam, dark brown (10YR 4 /3 ) moist; massive; hard, s lig h tly sticky and s lig h tly p la s tic ; few, fin e tubular pores; neutral (pH 6 .8 ). 252 Pedon Number: D Location: Riverside Co., Ca., bank cu tting , 0.75 m ile (1.2 km) east of Armstrong Road, elevation 1280 fe e t (397 m), S W corner of N E quarter sec. 4, T.2S, R.5W. Physiography: Mid-Pleistocene Jurupa Surface (T2). Surface forms abandoned valley and wind gap surface. C la s s ific a tio n : R elict s o il, Typic Haploxeralf. A 1 0-2" (0-5 cm)--Yellowish brown (10YR 5 /4 ) coarse sandy loam, dark brown (10YR 5 /3 ) moist; weak, fin e and medium, granular structure; s o ft, loose, nonsticky and nonplastic; common, very fin e and fin e roots; many, very fin e irre g u la r pores; s lig h tly acid (pH 6 .2 ); abrupt, smooth boundary. (1 to 6 inches [3 to 15 cm] thick) A12 2-5" (5-13 cm)— Brown (7.5YR 5 /4 ) coarse sandy loam, dark brown (7.5YR 4 /4 ) moist; weak, medium granular structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; common, fin e roots; many, fin e irre g u la r pores; neutral (pH 6 .8 ); abrupt, smooth boundary. (4 to 6 inches [10 to 15 cm] th ick) B21 5-10" (13-25 cm)--Reddish brown (5YR 4 /4 ) coarse sandy loam, dark reddish brown (5YR 3 /4 ) moist; moderate, subangular blocky struc ture; hard, firm , s lig h tly sticky and s lig h tly p la s tic ; common, fin e roots; common, very fin e irre g u la r pores; s lig h tly alkalin e (pH 7 .6 ); c le a r, smooth boundary. (9 to 20 inches [23 to 50 cm] th i ck) B22t 10-15" (25-45 cm)— Yellowish red (5YR 5/6) sandy clay loam, reddish brown (5YR 4 /4 ) moist; moderate, medium prismatic structure; hard, firm , s lig h tly sticky and s lig h tly p la s tic ; common, fin e roots; common, fin e irre g u la r pores; neutral (pH 7 .2 ); gradual, smooth boundary. (7 to 12 inches [18 to 30 cm] th ick) B3 18-23" (45-58 cm)--Yellowish red (5YR 4 /5 ) coarse sandy loam, reddish brown (5YR 4 /3 ) moist; weak, medium subangular blocky structure; hard, fr ia b le , nonsticky and nonplastic; few, fin e roots; few, fin e irre g u la r pores; neutral (pH 6 .7 ); c le a r, smooth boundary. (4 to 12 inches [10 to 30 cm] th ick) C 23-38" (58-93 cm)— Reddish yellow (7.5YR 6 /6 ) weathered granodiorite; massive; extremely hard, firm , nonsticky and nonplastic; s lig h tly acid (pH 6 .4 ). 253 Pedon Number: E Cieneba Series Location; San Bernardino Co., Ca., Jurupa Surface, 0.75 miles (1.2 km) east of Armstrong Road, elevation 1300 fe e t (397 m), north quarter corner sec. 4, T .2 S ., R.5W. Physiography: Roadcut in track descending from Jurupa Surface. C la s s ific a tio n : Loamy, mixed, nonacid, thermic, shallow Typic Xerorthents. A ll 0-6" (1-15 cm)--Yellowish brown (10YR 5 /4 ) sandy loam (12 percent fine g ra in ), dark brown (10YR 3 /3 ) moist; weak, medium and coarse, granular structure; s o ft, very fr ia b le , nonsticky and nonplastic; many fine and very fin e roots; many very fin e and fin e , irre g u la r pores; medium acid (pH 5 .8 ); c le a r, wavy boundary. (4 to 9 inches [10 to 23 cm] th ick) A12 6-16" (15-40 cm)--Yellowish brown (10YR 5 /4 ) sandy loam (10 percent g ravel), dark brown (10YR 4 /3 ) moist; weak, medium and coarse, subangular blocky structure; s lig h tly hard, very fr ia b le , nonsticky and non p la s tic ; com m on very fine and fin e roots; com m on very fin e and fin e irre g u la r pores; medium acid (pH 6 .0 ); c le a r, irre g u la r boundary. (4 to 14 inches [10 to 35 cm] th ick) Cl 16-23" (40-58 cm)--Light yellowish brown (10YR 6 /4 ) gravelly coarse sandy (approximately 50 percent rock fragments), yellowish brown (10YR 5/4) moist; massive; hard, fr ia b le , nonsticky and nonplastic, common, very fin e roots; few very fin e and fin e pores; s lig h tly acid (pH 6 .3 ); abrupt, irre g u la r boundary. (5 to 15 inches [12 to 38 cm] th ick) C2 23" (58 cm)--Weathered granodiorite, coarse jointed and shattered, and lig h t yellowish brown (10YR 6 /4 ) gravelly coarse grus, yellowish brown (10YR 5 /4 ) moist; com m on fin e and very fin e roots in the fracture jo in ts . 254 Pedon Ninnber: F Vista Series Location: Riverside Co., Ca., new housing development sewer trench, 1000 yards (915 m) south of Van Buren Road, Mockingbird Canyon, elevation 1200 fe e t (372 m), southwest corner of sec. 27, T .3 S ., R.5W. Physiography: Jurupa Surface (T2). C la s s ific a tio n : Coarse-loamy, mixed thermic Typic Xerochrepts. A1 0-3" (0-8 cm)—Dark yellowish brown (10YR 4 /4 ) sandy loam, dark brown (10YR 3 /3 ) moist; weak, medium, granular structure; s lig h tly hard, very fr ia b le , nonsticky and nonplastic; many very roots; common, fin e , irre g u la r pores; s lig h tly acid (pH 6 .2 ); abrupt, clear boun dary (2 to 6 inches [5 to 15 cm] th ick) A2 3-14" (8-35 cm)--Brown (10YR 5 /3 ) coarse sandy loam, brown (10YR 4 /3 ) moist; medium, granular structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; many fin e foots; common, fin e , irre g u la r pores; s lig h tly acid (pH 6 .5 ); c le a r, wavy boundary. (8 to 16 inches [20 to 40 cm] th ick) B2 14-26" (35-65 cm)— Yellowish brown (10YR 5 /6 ) coarse sandy loam, dark brown (10YR 4 /3 ) moist; weak, medium subangular blocky structure; hard, fr ia b le , nonsticky and nonplastic; many, fin e roots; many, fin e , irre g u la r pores; neutral (pH 6 .8 ); c le a r, smooth boundary. (8 to 14 inches [20 to 35 cm] thick) C 26-40" (65-101 cm)—Brownish yellow (10YR 6 /6 ) decomposed g ran itic rock; s lig h tly acid (pH 6 .5 ). 255' Pedon Number: G Buren Series Location: Riverside Co., Ca., Limonite Surface, 1000 fe e t (305 m) north of junction Canyon Crest Road and Country Club D rive, elevation 1180 fe e t (360 m), northeast quarter corner of sec. 6, T .3 S ., R.4W. Physiography: Bankcut in old a llu v ia l fan surface, fe e t. C la s s ific a tio n : Fine, loamy, mixed, therm ic, Haplic D urixeralfs. A1 0-6" (0-15 cm)—Brown (10YR 5 /3 ) fin e sandy loam, dark brown (10YR 3/3) moist; weak, coarse granular structure; hard, fr ia b le , s lig h tly sticky and p la s tic ; common, fin e , random roots; com m on fine tubular pores; moderately a lkalin e (pH 8 .0 ); abrupt, smooth boundary. (6 to 10 inches [15 to 25 cm] thick) B21t 6-18" (15-45 cm)--Brown (7.5YR 5 /4 ) clay loam, dark brown (7.5YR 4 /4 ) moist; strong, coarse angular blocky structure; very h a rd .v e ry firm , very sticky and very p la s tic ; few, fin e , random roots; common, fin e , tubular pores; many moderately thick clay film s on ped faces; moderately alkalin e (pH 8 .0 ); gradual, smooth boundary. (8 to 12 inches [20 to 30 cm] th ick) B22t 18-29" (45-73 cm)— Light brown (7.5YR 6 /4 ) clay loam, brown (7.5YR 4 /4 ) moist; moderate, fin e , angular blocky structure; very hard, very firm , sticky and p la s tic ; few, fin e , random roots; common, fin e tubular pores; common, moderately thick clay film s on ped surfaces; moderately alkalin e (pH 8 .4 ); c le a r, smooth boundary. (9 to 12 inches [23 to 30 cm] th ick) B3ca 29-35" (73-88 cm )--Light o live brown (2.5YR 5/4) loam, o live brown (2.5Y 4 /4 ) moist; massive, very hard, very firm , s lig h tly sticky and p la s tic ; few, fin e roots; common, fin e tubular pores; a few fin e clay film s on tubular pores; moderately alkaline (pH 8 .4 ); s lig h tly effervescent; fin e threads of calcium carbonate; c le a r, smooth boundary. (5 to 8 inches [13 to 20 cm] th ick) Clsj 35-44" (88-110 cm)--Yellowish brown (10YR 5 /4 ) cemented loam, dark yellowish brown (10Y R 4 /4 ) moist; very thick tabular la y e r, coated with thin lime and s ilic a partings, lig h t brownish gray (10YR 6/2) when dry; very hard, very firm , s lig h tly sticky and p la s tic , few, fin e tubular pores; moderately a lk a lin e , (pH 8 .4 ); s lig h tly e ffe r vescent; gradual smooth boundary. (6 to 10 inches [15 to 25 cm] th ick) C2sj 44-50" (110-125 cm )--Light yellowish brown (10YR 6/4) cemented loam, dark brown (10YR 4 /3 ) moist; massive, approximately 40 percent forms durinades; very hard, very firm , s lig h tly sticky and p la s tic , mod e rately alkalin e (pH 8 .4 ); s lig h tly effervescent; carbonate forms thin threads. 2 5 6 Pedon Number: H Monserate Series Location: Riverside Co., Ca., railw ay cut, .3 miles (0.6 km) west of Jurupa Railway Bridge, elevation 790 fe e t (242 m), N W corner of sec. 30, T .2 S ., R.5W. Physiography: Limonite Surface (T4). Surface is bypassed by small g ullies extending headwards from Santa Ana River. C lassificatio n: Fine loamy, mixed, therm ic, Typic D urixeralf Ap 0-16" (0-40 cm)--Dark brown (7.5YR 4 /4 ) sandy loam, dark brown (7 .SYR 3/2) moist; coarse granular structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; com m on fin e roots; many fin e , tubular pores; s lig h tly acid (pH 6 .2 ); abrupt, smooth boundary. (8 to 16 inches [20 to 40 cm] thick) A1 16-24" (40-60 cm)— Reddish brown (5YR 4 /4 ) sandy loam, dark reddish brown (SYR 3 /4 ) moist; medium angular blocky structure; s lig h tly hard, firm , s lig h tly sticky and s lig h tly p la s tic ; many fin e roots; common, fin e tubular pores; s lig h tly acid (pH 6 .4 ); c le a r, smooth boundary. (5 to 10 inches [13 to 25 cm] th ick) B21t 24-36" (60-90 cm)--Yellowish red (SYR 5/6) sandy clay loam, reddish brown (SYR 4 /4 ) moist; medium columnar structure; hard, firm , sticky and p la s tic ; few fin e roots; common, thin clay film s on ped faces and grains; neutral (pH 7 .0 ); gradual, smooth boundary. (9 to 13 inches [23 to 33 cm] th ick) B22t 36-43" (90-108 cm)--Reddish brown (SYR 5/3) sandy clay laom, reddish brown (SYR 4 /4 ) moist; strong, medium, angular blocky structure; very hard, very firm , sticky and p la s tic ; many thick clay film s on ped faces, sand grains and in fillin g pores; neutral (pH 7 .0 ); gradual, smooth boundary. (6 to 10 inches [15 to 25 cm] th ick) o 1 — » U ) 43-60: (108-150 cm)--Yellowish brown (10YR 5 /6 ) duripan, reddish brown (5YR 4 /3 ) moist; massive; manganese and lime in fractures; m ildly a lkalin e (pH 7 .4 ); gradual, smooth boundary. (10 to 18 inches [25 to 45 cm] th ick) C 2 60-71" (150-178 cm)--Yellowish brown (10YR 5 /6 ) loamy coarse sand, reddish brown (SYR 4 /3 ) moist; massive, weakly cemented; very hard, very firm , nonsticky and nonplastic; m ildly alkalin e (pH 7 .4 ); gradual, smooth boundary. (9 to 14 inches [23 to 35 cm] th ick) C3 71-86" (178-216 cm)—Yellowish brown (10YR 5/4) coarse sand, brown (7.5YR 5 /4 ); massive, weakly cemented and tra n s itio n a l to weathered granite. 257 Pedon Number: I Soil Strati graphic Section Location: Riverside Co., Ca., Hamner Bridge c l i f f section, north-facing c l i f f , 50 yards (47 m) north Riverside D rive, elevation 650 fe e t (202 m), N W corner sec. 6, T3S, R.6W. Physiography: V ertical c l i f f section, top of c l i f f continuous with Riverside Grand Terrace Surface (T5). C la s s ific a tio n : Surface s o il, Ramona Series, fine-loam y, mixed thermic Typic Haploxeralfs, overlies two fo ssil Typic Haploxeralfs and be low sequence of floodplaing Entisols and Inceptisols. Number in bracket below horizon c la s s ific a tio n refers to soil sample collection and located on diagram of c l i f f section (Figure 23). A1 0-11"—Yellowish brown (10YR 2/6) sandy hard, fr ia b le , s lig h tly (1) sticky and s lig h tly p la s tic ; few fin e roots; few, fin e , tubular pores; s lig h tly acid (pH 6 .2 ); c le a r, smooth boundary. B 1 l l " - 2 ' — Yellowish brown (10YR 5/6) sandy loam, dark yellowish brown (2) (10YR 4/4) moist; moderate coarse angular blocky structure; hard, fr ia b le , s lig h tly sticky and p la s tic ; com m on fin e tubular pores; s lig h tly acid (pH 6 .5 ); c le a r, smooth boundary. B2t 2 ‘ - 4 ‘ --Strong brown (7.5YR 5/6) sandy clay loam, dark brown (7.5YR 4/4) (3) moist; moderate coarse, angular blocky structure; hard, fr ia b le , sticky and p la s tic ; few, fin e tubular pores; s lig h tly acid (pH 6 .3 ); c le a r, smooth boundary. C 4 ’ - 5 ‘ 3"— Light yellowish brown (10YR 6 /4 ) sandy loam, dark brown (4) (10YR 4/3) moist; coarse subangular blocky structure; s lig h tly hard, firm , s lig h tly sticky and s lig h tly p la s tic ; few, fin e , tubu la r pores; m ildly alkalin e (pH 7 .8 ); s lig h tly effervescent; lime occurs in filam ents; gradual, smooth boundary. Cca 5'3"-6'6"~R eddish yellow (7.5YR 6 /6 ) loam, brown (7.5YR 5/4) moist; (5) massive; very hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; few, fine pores; moderately alkalin e (pH 8 .0 ); v io le n tly e ffe r vescent; lime throughout in thin seams; abrupt, smooth boundary. IIB 2 tb 6 '6"-9'--Y ello w ish red (5YR 5/3) Sandy loam, reddish brown (5YR 4/4) (5A) moist; strong, medium and coarse, prismatic structure; very hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; common, moderately thick clay film s on ped faces; continuous manganese film s on ped faces; lime occurs coating some ped faces; moderately alkalin e (pH 8 .0 ); gradual, smooth boundary. IlCca 91 - 9 110"—Very pale brown (10YR 7 /3 ) fin e sandy loam, yellowish brown (6) (10YR 5/4) moist; massive; very hard, very firm , nonsticky and non p la s tic ; moderately alkalin e (pH 8 .2 ); v io le n tly effervescent; lime forms nodular concretions; abrupt, smooth boundary. N.B. - Soil carbonate dated as 97,500 years B.P. ± 5,000 IIIB 1 9'10"-10'4"— Light yellowish brown (10YR 6/4) s ilt y , clay loam, (7) dark brown (10YR 4/3) moist; moderate, medium and coarse, sub angular blocky structure; hard, firm , nonsticky and nonplastic; neutral (pH 7 .0 ); c le a r, smooth boundary. '2 5 8 m e (8) 1 0 '4 " -ll'--P a le brown (10YR 6/3) lig h t, s ilty clay loam , brown (10YR 5 /3 ) moist; massive; hard, very firm , s lig h tly sticky and p la s tic ; neutral (pH 7 .0 ). IllC ca 111-1 3 '--W hite (10YR 8 /2 ) strongly cemented nodular carbonate horizon, pale brown (10YR 6 /3 ) moist; moderately alkalin e (pH 8 .0 ); vio le n tly effervescent; abrupt, smooth boundary. IV A . (9) 131 -1 6 11"—Very pale brown (10YR 7/4) s ilty clay, yellowish brown (10YR 5/4) moist; moderate, medium, subangular blocky structure; very hard, firm , s lig h tly sticky and p la s tic ; moderately alkaline (pH 8 .0 ); s lig h tly effervescent; gradual, smooth boundary. IVCk (10) 1 6 '1"-16'6"--W hite (10YR 8/2) strongly cemented nodular carbonate horizon, pale brown (10YR 6/3) moist; moderately alkalin e (pH 8 .4 ); vio le n tly effervescent; abrupt, smooth boundary. Sequence of channel gravel deposits encrusted in Ca+ overbank s ilts 161 6" - 19'2". VAIk (11) 1 9 '2"-20‘ --Very pale brown (10YR 7/3) s ilty clay loam, pale brown (10YR 6 /3 ) moist; moderate, fin e , and medium subangular blocky structure; hard, fr ia b le , s lig h tly sticky and p la s tic ; dark reddish brown (5YR 3/2) filam ents, possibly roots occur through horizon; neutral (pH 7 .0 ); gradual, smooth boundary. VCca (12) 20'-20*6"— Light gray (10YR N7/) weakly cemented carbonate horizon; gray (10YR N6/) moist; s o ft, fr ia b le , nonsticky and nonplastic; moderately alkaline (pH 8 .2 ); v io le n tly effervescent; clear, smooth boundary. VIA1 (13) 2 0 '6"-22' — Li ght yellowish brown (10YR 6 /4 ) clay loam, yellowish brown (10YR 5/4) moist; moderate, fin e and medium, subangular blocky peds; hard, fr ia b le , s lig h tly sticky and s lig h tly p lastic; moderately alkalin e (pH 8 .2 ); v io le n tly effervescent; lime occurs in soft masses; c le a r, smooth coundary. VICca (13A) 2 2 '-2 2 '6 "— Light gray (2.5Y 7/2) strongly cemented nodular horizon, graysh brown (2.5Y 5/2) moist; massive; hard, fr ia b le , nonsticky and nonplastic; moderately alkalin e (pH 8 .2 ); v io le n tly e ffe r vescent; c le a r, smooth boundary. VIIA 1 (14) 22 '6"-25'--V ery pale brown (10YR 7/4) s ilty clay loam, lig h t brownish gray (10YR 6 /2 ) moist; massive; s lig h tly hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; m ildly alkalin e (pH 7 .6 ); s lig h tly effervescent; c le a r, smooth boundary. VUCca (15) 2 5 '-2 5 1 4"— Light gray (2.5Y 7/2) strongly cemented s ilty sand h ori zon, grayish brown (2.5Y 5/2) moist; massive; very hard, very firm , nonsticky and nonplastic; moderately alkalin e (pH 8 .0 ); v io len tly effervescent; c le a r, smooth boundary. V IIIA (17) 2 5 '4 "-2 6 '6 "--L ig h t grayish brown (2.5Y 6 /4 ) fin e sandy loam, grayish brown (2.5Y 5/2) moist; massive; s lig h tly hard, fr ia b le , non sticky and nonplastic; moderately a lkalin e (pH 8 .0 ); strongly effervescent; c le a r, smooth boundary. v in e (18) 2 6 '6 "-2 7 ‘ --L ig h t gray (10YR 6 /2 ) loamy sand, gray (10YR 6/1) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; mod erately alkalin e (pH 8 .4 ); v io le n tly effervescent; li'me occurs in threads and soft masses; abrupt, clear boundary. IXA (HB1) 2 7 '-27'0"--V ery pale brown (10YR 7/3) loamy fin e sand, pale brown (10YR 6 /3 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; s lig h tly acid (pH 6 .4 ); c le a r, abrupt boundary. 259 IXBl IXC IXCca2 X A (HB2) X B XB 2 X C XIA (HB3) XIB1 XIB21 XIB22 XIC 2 7 '9"-2 9 '6 "~ P a le brown (10YR 6 /3 ) sandy loam, dark brown (10YR 4/3) moist; weak, medium subangular blocky structure; s lig h tly hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; neutral (pH 6 .8 ); cle a r, gradual boundary. 29'6"-30'2"--G rayish brown (10YR 5/2) sandy loam, dark grayish brown (10YR 4 /2 ); massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; m ildly alkaline (pH 7 .6 ); gradual, smooth boundary. 3 0 '2"~31' —Li ght gray (2.5Y 7/2) loam, grayish brown (2.5 Y 5/2) moist; massive; hard, firm , s lig h tly sticky and s lig h tly p lastic; moderately alkalin e (pH 8 .2 ); v io le n tly effervescent; abrupt, smooth boundary. 31'-32'8" - Floodplain s ilts and clay laminations. 231 8"-3311"--Pale yellow (10YR 7 /4 ) loamy fin e sand, brown (10YR 5/3) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; neutral (pH 6 .8 ); c le a r, smooth boundary. 3 3 'l"-34'--B row nish yellow (10YR 6/6) fin e sandy loam, yellowish brown (10YR 5/4) moist; weak, fin e subangular blocky structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; neutral (pH 6 .6 ); cle a r, smooth boundary. 341-3 4 14"--P ale brown (10YR 6/3) fin e sandy loam, brown (10YR 5 /3 ) moist; weak, medium subangular blocky structure; hard, fr ia b le , nonsticky and nonplastic; neutral (pH 6 .8 ); gradual, smooth boundary. 34 '4"-35'6"--P ale yellow (10YR 7 /4 ) loamy fin e sand, pale brown (10YR 6 /3 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; neutral (pH 7 .2 ); abrupt, smooth boundary. 4" layer of thin clay partings plus fin e s ilty horizon. 36'-37'4"^— Li ght yellowish brown (2.5Y 6/4) fin e , sandy loam, grayish brown (2.5Y 5/2) moist; massive; s lig h tly hard, fria b le , nonsticky and nonplastic; m ildly alkalin e (pH 7 .6 ); abrupt, smooth boundary. 3 7 '4 " -3 7 'll" --L ig h t yellowish brown (10YR 6 /4 ) fin e , sandy loam, brown (10YR 5 /3 ) moist; weak, fin e subangular blocky structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; neutral (pH 6 .8 ); smooth, clear boundary. 3 7 'll" -3 8 '4 " — Yellowish brown (10YR 5 /4 ) fin e , sandy loam, dark yellowish brown. (10YR 4 /4 ) moist; moderate, medium and fin e sub- angular blocky structure; hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; neutral (pH 6 .8 ); gradual, smooth boundary. 3 8 '4 "-3 9 '--P a le brown (10YR 6 /3 ) fin e , sandy loam, dark brown (10YR 4 /3 ) moist; moderate, fin e subangular blocky structure; s lig h tly hard, fr ia b le , nonsticky and s lig h tly p la s tic ; neutral (pH 6 .6 ); gradual, irre g u la r boundary. 3 9 ' _4o■--Very pale brown (10YR 7 /4 ) sandy loam, brown (10YR 5/3) moist; massive; hard, fria b le , nonsticky and nonplastic; neutral (pH 6 .6 ). Below th is soil is a sequence of fin in g upwards flu v ia l deposits. 2 6 ° Pedon Nimber: J Ramona Series Location: Riverside Co., C a., north-facing road cut, f i f t y yards north of junction of Beach S treet and Jurupa Road, Pedley, 690 fe e t (214 m), SE corner of sec. 22, T.2S, R.6W. Physiography: Pedley Surface, Pleistocene Terrace. C lassification: Fine-loamy, mixed, thermic, Typic Haploxeralf over buried D urixeralfs. A1 0-10" (0-25 cm)— Brown (10YR 4 /3 ) fin e sandy loam, dark brown (10YR 3/3) moist; weak, fin e , granular structure; s o ft, very fr ia b le , nonsticky and nonplastic; few fin e roots; many, very fin e , and fin e , irre g u la r pores; medium acid (pH 6 .0 ); c le a r, smooth boundary. (6 to 14 inches [15 to 35 cm] th ick) A12 10-20" (25-50 cm)--Brown (10YR 4 /3 ) fin e sandy Toam, dark brown (10YR 3/3) moist; massive; hard, very fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; few fin e roots; common, fin e , irre g u la r pores; s lig h tly acid (pH 6 .3 ); c le a r, smooth boundary. (8 to 14 inches [20 to 35 cm] th ick) B 1 20-27" (50-68 cm)--Strongbrown (7.5YR 5 /6 ) loam, reddish brown (5YR 4 /4 ) moist; moderate, coarse subangular blocky structure; hard, fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; few fin e roots; many, fin e irre g u la r pores; few, thin clay film s on ped faces; s lig h tly acid (pH 6 .2 ); c le a r, smooth boundary. (5 to 8 inches [13 to 20 cm] th ick) B21t 27-35" (68-88 cm)--Reddish brown (5YR 4 /4 ) sandy clay loam, yellowish red (5YR 4 /6 ) moist; moderate, coarse prism atic structure; very hard, firm , sticky and p la s tic ; few fine roots; common, fin e irre g u la r pores; common, thin clay film s on ped faces and coating grains; s lig h tly acid (pH 6 .2 ); c le a r, smooth boundary. (6 to 10 inches [15 to 25 cm] th ick) B22t 35-42" (88-105 cm)--Yellowish red (5YR 5 /6 ) sandy clay loam, yellowish red (5YR 4 /6 ) moist; moderate, coarse, prism atic structure; very hard, very firm , sticky and p la s tic ; few fin e roots; few, fin e , irre g u la r pores; many thick clay film s on ped faces and grains; s lig h tly acid (pH 6 .2 ); gradual, smooth boundary. (5 to 10 inches [13 to 25 cm] th ick) B23t 42-52" (105-130 cm)— Yellowish red (5YR 5 /6 ) sandy clay loam, yellowish red (5YR 4 /6 ) moist; moderate, coarse, prism atic structure; very hard, very firm , sticky and p la s tic ; many moderately thick clay film s on ped surfaces and grains; s lig h tly acid (pH 6 .2 ); gradual, smooth boundary. (8 to 12 inches [20 to 30 cm] th ick) B3 52-66" (130-165 cm)— Yellowish red (5YR 5/6) sandy clay loam, yellowish red (5YR 4 /6 ) moist; moderate, coarse, angular blocky structure; very hard, very firm , sticky and p la s tic ; few, fin e , irre g u la r pores; thick clay film s on peds; neutral (pH 7 .0 ); c le a r, irre g u la r boun dary. (8 to 14 inches [20 to 35 cm] thick) 2 6 1 Cl 66-84" (165-210 cm)--Strong brown (7.5YR 5/6) fin e , sandy loam, dark brown (7.5YR 4 /4 ) moist; massive; hard, firm , s lig h tly sticky and p la s tic ; neutral (pH 6 .8 ); abrupt, smooth boundary. (10 to 20 inches [25 to 50 cm] th ick) C2sim 84-99" (210-248 cm)--Red (2.5YR 5 /3 ) coarse sandy loam hardpan, reddish brown (2.5YR 4 /3 ) moist; massive; extremely hard, ex tremely firm , strongly cemented; sedimentary structure indicates grading upwards; neutral (pH 7 .0 ); abrupt, wavy boundary. (10 to 15 inches [25 to 38 cm] th ick) B21tb 99-109" (248-272 cm)--Yellowish brown (10YR 5/6) fin e sandy loam, dark brown (7.5YR 4 /4 ) moist; moderate subangular blocky structure: very hard, firm , sticky and p la s tic ; thin clay film s on ped faces; s lig h tly acid (pH 6 .5 ); gradual, smooth boundary. (6 to 12 inches [15 to 30 cm] th ick) B22tb 109-131" (272-328 cm)— Red (2.5YR 4 /6 ) sandy loam, dark red (2.5YR 3/6) when moist; strong, medium and coarse angular blocky structure; hard, firm , s lig h tly sticky and p la s tic ; medium clay film s on ped faces; neutral (pH 6 .8 ); abrupt, smooth boundary. (15 to 32 inches [38 to 8 cm] th ick) Csim 131-142" (328-355 cm )--Light reddish brown (2.5YR 6 /4 ) coarse sandy hardpan, reddish brown (2.5YR 4 /4 ) moist; massive, extremely hard, extremely firm ; strongly cemented; sedimentary structure indicates grading upwards;-neutral (pH 7 .0 ); abrupt, smooth boundary. (9 to 14 inches [23 to 35 cm] th ick) Cl 142-165" (355-413 cm)— Red (2.5YR 4 /6 ) sandy loam, dark reddish brown (3.5YR 3/4) moist; moderate, fin e , prismatic structure; hard, firm , s lig h tly sticky and p la s tic ; fin e clay film s on ped faces; neutral (pH 6 .8 ); gradual, smooth boundary (15 to 20 inches [38 to 63 cm] th ick) Csi 165-180" (413-450 cm)— Light reddish brown (2.5YR 6 /4 ) coarse sandy hardpan, reddish brown (2.5YR 4 /4 ) moist; massive; extremely hard, extremely firm ; strongly cemented; netural (pH 7 .0 ). 2 6 2 Pedon Number: K Buchenau Series Location : Riverside Co., Ca., junction of Van Buren and Jurupa Road, A rling ton, elevation 730 fe e t (223 m) northeast corner of sec. 36, T .2S ., R.5W. Physiography: West-facing roadside cut, Pedley Surface. C lassificatio n : Fine-loamy, mixed, thermic Typic D urixeralfs overlying buried C alcixeralfs. Ap 0-5" (0-13 cm)— Brown (10YR 4 /3 ) loam, dark brown (10YR 3 /3 ) moist; weak, granular structure; s o ft, very fr ia b le , s lig h tly sticky and p la s tic ; many fin e and very fin e roots; common, fin e and very fin e , tubular pores; moderately a lk a lin e (pH 8 .0 ); s lig h tly effervescent; gradual, smooth boundary (30 to 8 inches [8 to 20 cm] th ick) A1 5-12" (13-30 cm)— Brown (10YR 5 /3 ) loam, dark brown (10YR 3/3) moist; moderate, medium, subangular blocky structure; s lig h tly hard, fr ia b le , s lig h tly sticky and p la s tic ; many fin e roots; common, fin e and very fin e tubular pores; moderately alkalin e (pH 8 .0 ); s lig h tly effervescent; gradual, wavy boundary. (5 to 9 inches [3 to 23 cm] th ick) B21t 12-18" (30-46 cm)— Yellowish brown (10YR 5 /6 ) loam, dark yellowish brown (10YR 4 /4 ) moist; strong, medium, subangular blocky struc ture; hard, firm , sticky and p la s tic ; many fin e roots; conranon, fin e , tubular pores; moderately alkalin e (pH 8 .0 ); s lig h tly effervescent; gradual, smooth boundary. (5 to 8 inches [13 to 20 cm] th ick) IIB 22t 18-27" (30-69 cm)— Brown (10YR 5 /3 ) loam, dark yellowish brown (10YR 3/4) moist; strong, coarse and medium, blocky structure; hard, firm , sticky and p la s tic ; many fin e roots; common, fin e and very fin e , tubular pores; few, moderately thick clay film s on ped faces; moderately a lkalin e (pH 8 .0 ); s lig h tly effervescent; gradual, smooth boundary (8 to 10 inches [20 to 25 cm] th ick) 11 B3t 27-40" (69-100 cm)—Light yellowish brown (10YR 6 /4 ) loam, brown (10YR 5 /3 ) moist; massive; hard, firm , s lig h tly sticky and p la s tic ; coirmon, fin e roots; common, fin e , tubular pores; moderately alkalin e (pH 8 .0 ); strongly effervescent; abrupt, smooth boundary (10 to 16 inches [25 to 41 cm] thick) IIC1 40-50" (100-127 cm)— Light brownish gray (10YR 6 /2 ) loam, grayish brown (10YR 3 /2 ) moist; massive; hard, firm , s lig h tly sticky and p la s tic ; common, fin e roots; comnon, fin e , tubular pores; mod e ra te ly alkalin e (ph 8 .2 ); strongly effervescent; abrupt, smooth boundary. (9 to 14 inches [23 to 36 cm] th ick) IIC ca 50-60" (127-152 cm)—White (10YR 8 /2 ) strongly cemented hardpan, white (2.5Y 8 /2 ) moist; massive, breaking into horizontal layers; few , fin e roots; common, fin e tubular pores; strongly alkaline (pH 8 .8 ); v io le n tly effervescent; long filam ents of soft lime hang down from the hardpan; c le a r, smooth boundary. (8 to 15 inches [20 to 38 cm] th ick) 263 IIIB 21tb 60-108" (152-274 cm)—Light yellowish brown (10YR 6 /4 ) loam, yellowish brown (10YR 5/4) moist; strong, coarse and medium subangular blocky structure; hard, fr ia b le , sticky and p la s tic ; common, th in clay film s on ped faces; moderately alkalin e (pH 8 .0 ); strongly effervescent; fin e filam ents of s o ft lime; c le a r, wavy boundary. (25 to 50 inches [64 to 127 cm] th ick) IUCcab 108-116" (274-295 cm)—White (10YR 8 /2 ) strongly cemented hardpan, white (2.5YR 8 /2 ) moist; massive, breaking into nodular concre tions; strongly alkalin e (pH 8 .6 ); v io le n tly effervescent with disseminated lime; c le a r, wavy boundary. (8 to 10 inches [20 to 25 cm] th ick) IVB21tb 116-140" (295-356 cm)—Very pale brown (10YR 7 /4 ) loamy clay, yellowish brown (10YR 5 /4 ) moist; moderate, medium and fin e subangular blocky structure; hard, fr ia b le , sticky and p la s tic ; common, moderately thick clay film s on ped faces; moderately alkalin e (pH 8 .0 ); strongly effervescent; segregated lime occurs in soft masses; c le a r, wavy boundary. (15 to 25 inches [38 to 64 cm] thick) IVCcab 140-146" (356-371 cm)—White (10YR 8/2) strongly cemented hardpan, very pale brown (10YR 7/4) moist; massive, breaks into large nodular concretions; strongly a lkalin e (pH 8 .8 ); v io le n tly effervescent; c le a r, wavy boundary. (5 to 8 inches [13 to 20 cm] th ick) IVB2tb 146-182" (371-462 cm)—Reddish yellow (7.5YR 6 /6 ) clay loam, strong brown (7.5YR 5 /6 ) moist; moderate, fin e , subangular blocky struc ture; hard, fr ia b le , sticky and p la s tic ; common, moderately thick clay film s on ped surfaces; moderately a lkalin e (pH 8 .0 ); strongly effervescent; segregated lime occurs in thin filam ents; cle a r, wavy boundary. (30 to 50 inches [76 to 127 cm] thick) VCcab 182-197" (462-500 cm)—White (10YR 8 /2 ) strongly cemented hardpan, lig h t gray (10YR 7/2) moist; massive, breaks into irre g u la r large nodules; strongly alkalin e (pH 8 .6 ); v io le n tly effervescent; d iffu s e , irre g u la r boundary. (Horizon varies in thickness be tween 9 and 15 inches [23 and 38 cm] as i t extends into under lying stream gravel sequence and carbonate is the cementing agent) VC b 197-243" (500-630 cm)— Represents two sequences of cut and f i l l , im bricate, flu v ia l gravels. These gravels are extremely wea thered and cemented by carbonate. They o verlie an eroded, strongly weathered granite surface. This horizon represents a strath terrace surface. 264 Pedon Number: L Delhi Series Location: San Bernardino Co., Ca., west-facing stream cut, 300 yards (275 m) end of Santa Ana Avenue, elevation 960 fe e t (298 m), S W quarter sec. 25, T .1 S ., R.5W. Physiography: Stream bank eroded to show Wisconsin dune fie ld sands overlying a buried soil formed on well weathered sands and gravels of the Riverside Surface (T5). C lassificatio n: D elh i, mixed, thermic Typic Xeropsamments overlying a sandy, mixed, thermic Typic Haploxeralfs. A1 0-7" (0-18 cm)— Pale brown (10YR 6 /3 ) fin e sand, grayish brown (10YR 5 /2 ) moist; single grain; loose when dry or m oist, non- sticky and nonplastic; many, very fin e and fin e roots; s lig h tly acid (pH 6 .3 ); c le a r, smooth boundary. (8 to 14 inches [20 to 35 cm] th ick) Cl 7-20" (18-50 cm)— Light Yellowish brown (10YR 6 /4 ) fin e sand, brown (10YR 5 /3 ) moist; single grain; loose when dry or m oist, non- sticky and nonplastic; few, very fin e roots; s lig h tly acid (pH 6 .1 ); gradual, smooth boundary. (15 to 25 inches [38 to 63 cm] th ick) C 2 20-44" (50-110 cm)— Pale yellow (2.5Y 7 /4 ) fin e sand, grayish brown (2.5Y 5 /2 ) moist; massive; s lig h tly hard, very fr ia b le , s lig h tly sticky and nonplastic; s lig h tly acid (pH 6 .5 ). Dune composed of 23 fe e t (7.1 m) of this m aterial; overlies c le a r, smooth boundary of fo ssil s o il. IIA lb $ 0-16" (0-40 cm)—Reddish yellow (7.5YR 6 /6 ) sandy loam, brown (7.5YR 5 /4)m o ist; massive; s lig h tly hard, fr ia b le , non- sticky and nonplastic; s lig h tly acid (pH 6 .4 ); gradual, smooth boundary. (10 to 18 inches [25 to 45 cm] th ick) IIB lb 16-24" (40-60 cm)— Yellowish red (5YR 5 /6 ) coarse, sandy loam, reddish brown (5YR 4 /4 ) moist; weak, subangular blocky structure; s lig h tly hard, fr ia b le , nonsticky and nonplastic; s lig h tly acid (pH 6 .2 ); c le a r, smooth boundary. (8 to 14 inches [20 to 35 cm] th ick) IIB12b 24-34" (60-85 cm)— Reddish brown (5YR 5 /4 ) coarse sandy loam, reddish brown (5YR 4 /3 ) moist; moderate, angular blocky struc ture; hard, fr ia b le , nonsticky and nonplastic; s lig h tly acid (pH 6 .2 ); gradual, smooth boundary. (10 to 18 inches [25 to 45 cm] th ick) IIC lb 34-45" (85-113 cm)— Light brown (7.5YR 6 /4 ) coarse loamy sand, dark brown (7.5YR 4 /4 ) moist; massive; hard, fr ia b le , nonsticky and nonplastic; s lig h tly acid; gradual, smooth boundary. (10 to 18 inches [25 to 45 cm] th ick) IIC 2b 45-60" (113-150 cm)— Light yellowish brown (10YR 6 /4 ) coarse loamy sand, dark brown (10YR 4 /3 ) moist; massive; hard, fr ia b le , non sticky and nonplastic; s lig h tly acid (pH 6 .1 ). This overlies a sequence of fin in g upwards gravel and sand units which are illu s tra te d in Figure 22. 265; Pedon Nunber: M Tujunga Series Location: San Bernardino Co., Ca., 200 yards ( m) north, junction Riverside Avenue and Aqua Manson Road, southwest corner of section 35, T .1 S ., R.5W. Physiography: Gravel p it excavated in Wisconsin Lytle Creek Surface (T7). C la s s ific a tio n : Mixed, thermic, Typic Xeropsamments. A1 0-10" (0-25 cm)—Grayish brown (10YR 5 /2 ) sandy loam, dark brown (10YR 3 /3 ) moist; weak, fin e , granular structure; s o ft, very fr ia b le , non sticky and nonplastic; many very fin e and fin e roots; many very fin e tubular pores; neutral (pH 7 .0 ); c le a r, smooth boundary (6 to 14 inches [15 to 35 cm] th ick) C 10-60" (25-100 cm )--Light brownish gray (10YR 6 /2 ) bedded gravel and sand, gray (10YR 5/1) moist; single grain; loose when dry or m oist, nonsticky and nonplastic; neutral (pH 7 .0 ). 266 Pedon Ntanber: N Hilmar Series Location: Riverside Co., Ca., soil p it , 200 yards (186 m) north of Limonite, Pedley; elevation 660 fe e t (205 m), S W corner of sec. 22, T .2S ., R.6W. Physiography: Bottom of broad swale, Mira Lom a Surface (T8). C la s s ific a tio n : Sandy over loamy, mixed, calcareous, Hermic Aquic Xerortheuts. Ap 0-5" (0-13 me)— Yellowish brown (10YR 5 /6 ) loamy sand, dark yellowish brown (10YR 4 /4 ) moist; single grain; loose when dry or moist, non sticky and nonplastic; common, very fin e and fin e roots; moderately a lkalin e (pH 8 .0 ); s lig h tly effervescent; c le a r, smooth boundary (4 to 10 inches [10 to 25 cm] th ick) Al 5-14" (13-35 cm)—Light yellowish brown (2.5Y 6 /4 ) loamy sand, grayish brown (2.5YR 5 /2 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; common, fin e roots; moderately alkalin e (pH 8 .0 ); s lig h tly effervescent; c le a r, smooth boundary. (8 to 15 inches [20 to 38 cm] thick) Cl 14-25" (35-63 cm)— Light brownish gray (2.5Y 6 /2 ) sandy loam, lig h t o live brown (2.5YR 5/4) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; few medium roots; moderately alkalin e (pH 8 .2 ); s lig h tly effervescent; few, rounded, soft lime concretions; c le a r, smooth boundary. (5 to 12 inches [13 to 30 cm] thick) C 2 25-38" (63-95 cm)— Light gray (2.5Y 7 /2 ) sandy loam, gray (N5/) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; few fin e roots; moderately alkalin e (pH 8 .2 ); v io le n tly effervescent; few soft lime concretions and fin e threads. 267 Pedon Number: 0 GrangeviHe Series Location: San Bernardino Co., C a., Terrace T9, 1000 fe e t north of junction Pedley Road and Riverside D rive, Norco, N W corner of sec 32, T .2S ., R.6W. Physiography: Bankcut in floodplain terrace T9, 600 fe e t. C la s s ific a tio n : Coarse-loamy, mixed, thermic, Aquic Haploxerolls. Al 0-14" (0-35 cm)--Grayish-brown (2.5Y 5/2) loamy very fin e sand, very dark grayish brown (2.5Y 3/2) moist; massive; s o ft, very fr ia b le , nonsticky and nonplastic; many very fin e roots; few very fin e pores; moderately a lkalin e (pH 8 .2 ); s lig h tly effervescent; abrupt wavy boundary. (8 to 14 inches [20 to 35 cm] th ick) Cl 14-20" (35-50 cm)— Grayish-brown (2.5Y 5 /2 ) very fin e sandy loam, dark grayish brown (2.5Y 4 /2 ) when moist; massive; s o ft, very fr ia b le , s lig h tly sticky and s lig h tly p la s tic ; many, very fin e roots; few very fin e tubular pores and coranon very fin e , irre g u la r pores; moderately alkalin e (pH 8 .4 ); strongly effervescent; few fa in t m ottles; abrupt, irre g u la r boundary. (4 to 10 inches [10 to 25 cm] th ick) C2 20-41" (50-102 cm)--Grayish-brown (2.5Y 5 /2 ) loamy very fin e sand, dark grayish brown (2.5Y 4 /2 ) when moist; massive; s o ft, very fr ia b le , nonsticky and nonplastic; few, very fin e random roots; few very fin e tubular pores and many, very fin e , irre g u la r pores; moderately a l kaline (pH 8 .2 ); strongly effervescent; variable s i l t and fin e sand lenses 1 to 3 inches th ick; few fa in t m ottles; gradual wavy boun dary. (8 to 23 inches [20 to 58 cm] th ick) C3 41-56" (102-140 cm)--Grayish brown (2 .5Y 5 /2 ) loamy very fin e sand, dark grayish brown (2.5Y 4 /2 ) when moist; massive; s o ft, very fr ia b le , nonsticky and nonplastic; few very fine tubular pores; moderately a l kaline (pH 8 .4 ); strongly effervescent. Pedon Number: P Dello Series Location: San Bernardino Co., Ca., Terrace T10, 1800 fe e t north of junction Pedley Road and Riverside D rive, Norco, N E corner of sec 32, T .2 S ., R.6W. Physiography: Pedon excavated bankcut of T10 Surface near junction of open grove and closed cottonwood grove. C la s s ific a tio n : Mixed, therm ic, Typic Psammaquents. Al 0-6" (0-15 cm)--Grayish brown (2.5YR 5 /2 ) loamy sand, very dark grayish brown (10YR 3 /2 ) moist; weak, platy structure; s o ft, very fr ia b le , nonsticky and nonplastic; abundant very fin e and fin e roots; many, very fin e irre g u la r pores; moderately alkalin e (pH 8 .2 ); c le a r, smooth boundary. (5 to 12 inches [13 to 30 cm] th ick) Cl 6-14" (15-35 cm)— Light grayish brown (2.5YR 6 /2 ) loamy sand, very dark grayish brown (2.5YR 3 /2 ) moist; single grain, loose, nonsticky and nonplastic; abundant very fin e and fin e roots; many very fin e irre g u la r pores; moderately a lkalin e (pH 8 .4 ); c le a r, smooth boundary. (8 to 10 inches [20 to 25 cm] th ick) C2 14-35" (15-88 cm)— Light gray (2.5Y 7 /2 ) loamy sand, lig h t brownish, gray (2.5Y 6 /2 ) moist; single grain, loose, nonsticky and nonplastic; abundant fin e and few coarse roots; moderately alkalin e (pH 8 .2 ); c le a r, smooth boundary. (8 to 20 inches [20 to 50 cm] th ick) C3 35-52" (88-130 cm)— Light brownish gray (2.5Y 6 /2 ) loamy sand, very dark grayish brown (2.5Y 4 /2 ) moist; reddish brown (5YR 4 /3 ) m ottling; single grain, loose, nonsticky and nonplastic; many fin e and few coarse roots; moderately alkalin e (pH 8 .4 ). 26 9 Pedon Number: Q Hanford Series Location: Riverside Co., Ca., soil p it , 50 yards (47 m) south of Jurupa Road, Mira Loma, elevation 700 fe e t (217 m) SE corner of sec. 15, T .2 S ., R.6W. Physiography: Mira Lom a Surface (T8). Frequently found on d rie r sites while Hilmar Soil Series (Pedon N) found on wetter s ites. C la s s ific a tio n : Coarse, loamy, mixed, nonacid, Hermic Typic Xerorthents. Ap 0-10" (0-25 cm)--Pale brown (10YR 6 /2 ) sandy loam, dark grayish brown (10YR 4 /2 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; many very fin e roots; common, fin e irre g u la r pores; s lig h tly acid (pH 6 .4 ); gradual, smooth boundary. (5 to 12 inches [13 to 30 cm] thick) Cl 10-24" (25-60 cm)—Grayish brown (10YR 5 /2 ) sandy loam, dark gray (10YR 4 /1 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; few fin e roots; common, fin e , irre g u la r pores; neutral (pH 6 .8 ); c le a r, smooth boundary. (8 to 18 inches [20 to 45 cm] thick) C2 24-36" (60-90 cm)—Very pale brown (10YR 7 /3 ) coarse sandy loam, brown (10YR 4 /3 ) moist; massive; s lig h tly hard, fr ia b le , nonsticky and nonplastic; few, fin e roots; s lig h tly acid (pH 6 .5 ). TERRACE SURFACES AND LANDFORMS OF THE NORTHERN PERRIS BLOCK B ETW EEN RIVERSIDE AND CORONA CALIFORNIA [Of] ALLUVIAL FAN SURFACE o-r«eent, b-eld [C ] BRAIDED STREAM CHANNELS Q j] SAND DUNES jo g QUARRY DUMPS Q FLOOD CONTROL {J J INSELBERGS [ j ] TERRACE SURFACES t t Mountain front 8 margin of Perris and Paloma Surfaces 117° 30' \ T 4 \ T8 Qfa r — < Qfa I y / i '[ \ S 5 ® ^ \ K fK \ D “ > \ ! \ \ {p V \ W \ I I \ V \ ' O ^ I [Mj\/ FC T7 T3 FC JURUPA MOUNTAINS t-5: .A LOMA) I H IL L S - „|T4 / % V T5 A T4 T4 > T 4L T7 ' i Ur\\ ■v™\\ * 1 / ' T4 FC T i r't& BLUE MOUNTAIN Qfa S'* ' - - . - ' ' ’ 'T V >1 W f\\ V r . ® l i l » / > / I J \ i ' \ / ' / I I t ; i \' <\( / // T 6 f ; I I ;W .' M 4 \ T4 T3 H IL L S T7-8 \ J i ? //G V . V // T6 T6 r'J T5 T4 A . O I T9 W > 1 / A -t i T 4 ^ ''i . „ i\A— i ! A--~ ^ T5 )T2 > T3 S -? T'/O' J S T6 TIO T 9 / ' T I O _ ... A T9 T6 " S i c / O ' \ * N . \ 4 S 7 r^'\. .,s y y T4 —= ■ £ * < a r. TEQUESQUITE / SYCAMORE >T2 5 O ' ' f / T l O / ^ % ' ' i — /O' ■ 0 /VT5 & T5 c p ? c 1 c r \ T3 y- v?'/ / V •• • v HOUSING ,SbO? a T6 T4 T4 A <£s> $ A f y T4 ■ 7 3' V n C >iU'3T^ '%> o y /r PALOMA S U R FA CE A ( a A/ . <.TI \ C T I / V ^ ¥ / ' T4 TO' T4 T5 T4 m ' \ c \ / T4 T5 T4 - - ' ■ A . V • 5 SURFACE T5 T5 CORONA A LLU V IA L FAN "K \ <§} SURFACE A y - A FIGURE 19 SURFACE 3 4 ° 0 0 ‘ 2 . & 6 f e 117° 15'

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Creator Haner, Barbara Elizabeth (author)

Core Title Quaternary geomorphic surfaces on the northern Perris Block, Riverside County, California: Interrelationship of soils, vegetation, climate and tectonics

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geomorphology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c29-348165

Unique identifier UC11220715

Identifier DP28560.pdf (filename),usctheses-c29-348165 (legacy record id)

Legacy Identifier DP28560.pdf

Dmrecord 348165

Document Type Dissertation

Rights Haner, Barbara Elizabeth

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA