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Recent And Upper Pleistocene Sediments Of The Southwestern Portion Of Losangeles County, California

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Recent And Upper Pleistocene Sediments Of The Southwestern Portion Of Losangeles County, California

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Content This dissertation has been 65—9982 microfilmed exactly as received RICCIO, Joseph Frank, 1921— RECENT AND UPPER PLEISTOCENE SEDIMENTS OF THE SOUTHWESTERN PORTION OF LOS ANGELES COUNTY, CALIFORNIA. University of Southern California, Ph.D., 1965 Geology U n iversity M icrofilm s, Inc., A n n A rb or, M ichigan RECENT AND UPPER PLEISTOCENE SEDIMENTS OF THE SOUTHWESTERN PORTION OF LOS ANGELES COUNTY, CALIFORNIA by Joseph Frank Riccio 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 (Geology) June 1965 UNIVERSITY OF SOUTHERN CALIFORNIA TH E G R ADUATE SC HO O L U N IV E R S IT Y PARK LO S A N G ELES, C A L IF O R N IA 9 0 0 0 7 This dissertation, written by ...........J.o.&apk.F_r2vnk_JRiccia........... under the direction of his.....Dissertation Com mittee, and approved by all its members, has been presented to and accepted by the Graduate School, in partial fulfillment of requirements for the degree of D O C T O R O F P H IL O S O P H Y ....... ^ Dean Date J.une.,..19.65..................................... DISSERTATIO N C O M M IT T E E h d r n d jQtSS......... CONTENTS Page LIST OF ILLUSTRATIONS..................................viii LIST OF TABLES...................................... x ABSTRACT........................... 1 INTRODUCTION ........................................ 3 Location of a r e a ................................ 3 Purpose of investigation . . 5 j ! | Previous work 5 ; i Field methods 6 | Acknowledgments .................................. 7 Approach to problem ............................. 8 PHYSIOGRAPHY........................................ 9 General features ................... 9 Palos Verdes H i l l s .............................. 9 Newport-Inglewood Uplift ....................... 11 Baldwin Hills ....................... 12 Rosecrans Hills........................... . 12 Dominguez H i l l ............................. 13 'Chapter Page El Segundo Sand Hills............................ 14 Torrance Plain .................................. 14 G a p s ............................................. 15 Ballona G a p .................................. 15 Dominguez G a p ................................ 15 STRATIGRAPHY......................................... 17 Pleistocene Series ................. 17 General features ............................ 17 Palos Verdes Sand........................... 18 North border of the hills............... 19 Gaffey Anticline................... .. . 20 Baldwin Hills area .......... 21 Area north of the Palos Verdes Hills . . 24 Stratigraphic relationships ............. 30 Unnamed Upper Pleistocene deposits ............. 32 Physical character .......................... 32 Thickness.................................... 34 Stratigraphic relationships.................. 36 Pleistocene to Recent Series ................... 41 Nonmarine terrace cover ..................... 41 Chapter Page , i _ j General features ....................... 41 j . i i Physical character . .................... 42 I Recent Series........ ........................... 46 i Definition and general features . .......... 46 I Gardena Aquifer .............................. 47 General features ....................... 47 : A g e ...................................... 48 | . . Redondo Canyon.......................... 49 I Older dune sand............................. 51 j I General features ....................... 51 j i Thickness and physical character .... 51 I i Origin . .............................. 55 ! A g e ...................................... 5 5 Active dune s a n d ........................... 57 Fifty-foot gravel ........................... 58 i i Physical character....................... 58 j Origin............................... . . 59 A g e ..................... 60 Ancestral Los Angeles River ............ 61 Gap configuration ..... 64 IV Chapter Page Peat deposits.............. . 64 Brown spongy peat....................... 65 Black clayey peat 66 j j j Subsidence 67 : I I Gaspur Aquifer......................., . . . 67 ! Physical character ..................... 67 Origin.................................. 69 Alluvium 69 ! j Older alluvium......................... 70 Torrance F a n ............................ 73 Beach deposits.............................. 80 i Soils 81 ! j Sedimentary analyses ................... 82 Methods 82 j X-ray diffraction 82 j Coarse fraction analyses .......... 84 Grain s i z e ......................... 84 Consistency limits ................. 85 Carbon analysis............ 86 Alkalinity..................... 86 Chapter i Page Sulphate content ..................... 86 Results and conclusions ................. 86 X-ray diffraction..................... 86 i i I Coarse fraction analyses ............ 103 j | Grain s i z e ............................ 107 \ Consistency limits ................... 115 ; Carbon content ....................... 115 i Alkalinity........................... 118 ! Sulphate content.................. 119 ! i i Field relationships of the adobe soil .... 122 j Residual soils . . ..................... 123 i Adobe.................................. 123 ! Other residual soils . . . . . . . . 133 A g e .................................. 134 Transported adobe ............... .... 136 Adobe remnants................... 136 Torrance Plain ....................... 139 Other adobe remnants............... 148 BaIlona G a p ............................ 149 i ! jC hap ter Page I | A g e .................................... 150 i . ! Drainage pattern .......................... 151 RECENT-PLEISTOCENE BOUNDARY ........................... 154; I ! ; i RECENT MOVEMENT...................................... 157 i ^ | iSUMMARY................................................. 159 | i REFERENCES..................... ..................... 166 j i vii LIST OF ILLUSTRATIONS I Plate Page | I. Physiographic features of the southwestern portion of Los Angeles County............ pocketj II. Areal distribution of adobe soils III. Areal geology of the southwestern portion of Los Angeles County ............... IV. Subsurface geology of Redondo-Hermosa Beach area ....................... V. Subcrop limits of Ballona, Gardena and Gaspur Aquifer ..................... jFigure ! 1. Index map of study a r e a ...... .... 4 2. Palos Verdes S a n d ......................... 40 3. El Segundo Sand H i l l s ..................... 52 4. Areal distribution of the Torrance Fan . . . 74 5. Walteria Lake drainage s u m p ............... 77 6. Adobe soil in fault contact with the Altamira Shale ............................ 89 7. X-ray diffractometer traces of adobe soil...................................... 90 viii [Figure Page | 8. X-ray diffractometer traces of adobe 1 i soil...................................... 97 i 9 . Coarse fraction analysis ................. 105 | 10. Cumulative curves, residual adobe soil . . 108 j 11 • Cumulative curves, transported adobe soil • 110 12 * Cumulative curves, transported adobe soil • 111 | 13. Cumulative curves, residual clay soil . . • 114 : 14. Liquid limit-plasticity index .......... 116 15 . Adobe overlying diabase basalt of the Altamira Shale ......................... 124 i 16. Adobe overlying the Valmonte Diatomite . . • 125 17 . Adobe overlying the Altamira Shale .... 126 i is. 1 i Colluvial soil.......... ................ 127 i 19. 1 Adobe soil covering beach-graveIs .... 129 : 20. Adobe soil covering rubble . ............. 130 21. Consolidation curve, residual adobe . . . • 144 ; 22. Consolidation curve, transported adobe . . • 145 LIST OF TABLES jTable Page i 1. Fauna in sediments equivalent to Palos | Verdes a g e ................................... 25 i 2. Heavy mineral analysis ....................... 27 j 3. X-ray diffraction data, Manhattan Beach Clay c a p .........................................35 1 i 4. Thickness of the unnamed Upper Pleistocene deposits.................................... 37 5. X-ray diffraction data, Palos Verdes Hills . . 88 i ! 6. X-ray diffraction data, Dominguez and Baldwin Hills .............................. 92 j | 7. X-ray diffraction data, Rosecrans Hills . . . 94 8. X-ray diffraction data, Torrance Plain .... 95 i 9. X-ray diffraction data, Torrance Fan ......... 101 10. Stain test results, per cent of number of grains ....... ................... 104 i | 11. Comparison of quartile measures of residual i adobe soil................................... 109 ! 12. Comparison of quartile measures of trans ported adobe s o i l .......................... 112 13, Carbon analysis.............................. 117 x Table Page 14. pH and sulphate content of adobe soils .... 120 xi ABSTRACT The southwestern portion of Los Angeles County north- |ward from the Palos Verdes Hills to the Baldwin Hills is Underlain hy marine sediments of Late Upper Pleistocene age.; These sediments, the unnamed Upper Pleistocene deposits, are the stratigraphic equivalent of the Palos Verdes Sand which rests on the yotingest marine terrace of the Palos Verdes Hills. The Late Upper Pleistocene sediments represent shallow lagoonal, tidal or near-shore deposits from varying source areas and were deposited under rapidly changing conditions. The upper portion of the deposits is mainly fine-grained, consisting of sand, silt and clay, whereas the lower part is predominantly sand containing some gravel and subordinate amounts of silt and clay. Along the coast these deposits, -which attain a maximum thickness of 560 feet, are divided into 3 zones: the lower Redondo Tight zone, the overlying Merged Silverado zone and the upper Manhattan Beach Aqui- clude. A nonmarine terrace cover, Pleistocene to Recent in iage, is comprised of poorly sorted to unsorted rubble and jcrudely stratified gravelly sands which either overlie marine deposits of Pleistocene age which in turn rest on the wave-cut platforms or overlie the platforms per se of the 13: marine terraces of the Palos Verdes Hills. The terrace cover represents talus, slope and rill wash, fan detritus and landslide material which for the most part accumulated iafter emergence of the terraces. i Deposits of Recent age comprise sediments indicative of jlagoonal and littoral environments as well as those of eo- ! 'lian and fluvial origin. The Gardena Aquifer, a coarse-grained fluvial deposit jwhich extends inland from Redondo Beach across the Newport- j Inglewood uplift within the confines of the broad saddle between the Rosecrans Hills and Dominguez Hill, was deposit-} ed by an ancestral westward flowing river that incised its j 2 channel into the post-Upper Pleistocene deformational surface. Underlying Dominguez Gap and extending to San Pedro Bay, the Gaspur Aquifer, which consists of sand and gravel, was deposited by an ancestral San Gabriel River in Recent time. The petrology of the "50-foot gravel" indicates that this deposit which underlies Ballona Gap was deposited in part by Centinela Creek which drained the north slope of the Baldwin Hills and by several streams that drained the south slope of the Santa Monica Mountains. Interdistribu- tary and blanket peats which overlie the gravels indicate ithat a positive change in elevation resulting from subsi dence and/or an eustatic change in sea level occurred in the jlate Recent. ; A belt of aligned ridges and hills parallels the shore- tline from Ballona Gap to the Palos Verdes Hills and extends jinland to overlap the Torrance Plain. Sediments comprising jthese ridges and hills consist of a weathered and partially [cemented dune sand underlain by noncemented dune sands; an jintermediate zone of terrace deposits; and a lower horizon [consisting of beach gravels and sands. ’ Adobe soils on the Palos Verdes Hills, on the highs jalong the Newport-Inglewood Uplift and in the Torrance Plair iare differentiated as residual or transported on the basis iof field relationships and sedimentary parameters, namely, |x-ray diffraction and coarse fraction analysis. The trans ported adobe soils represent the latest cycle of alluviatior |of “ the region. i A subaerial origin and a Recent age is indicated for jRedondo and Santa Monica Canyons. The ancestral river that jincised Redondo Canyon deposited the Gardena Aquifer. Santc Monica Canyon was incised by the ancestral Los Angeles River. The Recent-Pleistocene boundary is marked by the with drawal of the Pleistocene sea and accompanying uplift. Late Recent crustal instability is shown by deposits of Upper Pleistocene and Recent age which are folded and faulted. I i I I F i INTRODUCTION Location of Area The area of study in the southwestern portion of Los Angeles County encompasses approximately 350 square miles abounded by the Pacific Ocean on the west and south, by longitude 118° 15' on the east and by latitude 34° 10' on the north (Fig. 1, Index map). The approximate dimensions of the area are 27 miles long and 13 miles wide. Within this area are 10 major physiographic provinces of Los Angeles County as shown on Plate I. Southwestern Los Angeles County is an area of tremendous expanding population and industrial growth. Because of the housing shortage, areas previously in agri culture and fallow land have been cut, leveled, and filled, (giving rise to soil and rock exposures not heretofore ! | javailable. Furthermore, the hundreds of borings required i to explore the land for housing developments, industrial j buildings and storm drain conveyances have produced a wealth! | of geologic data. The writer has been actively associated j — 118° 90' S f O f A N 6 £ L f S LOS INOLEWOOO COUNTY HAWTHORNE 6 A R 0 E N A TORRANCE ao‘ W1LMINOTON COUNTY MILES IN D E X MAP SHOWING LOCATION OF STUDY AREA FIGURE I iwith the urban geology of Los Angeles County for the past jlO years and thus the information obtained forms the basis i ;of this dissertation. Purpose of Investigation This study is concerned with the distribution of the Upper Pleistocene and Recent sediments as they occur within jthe area of study. Furthermore, the purpose of this study is to elucidate the recent geologic history of the region and to determine the origin and distribution of the surface adobe clays. Only those Pleistocene sediments of the Palos Verdes 'Hills which form an integral part of this report are dis- jcussed. Sediments older than the Palos Verdes Sand are for the most part omitted from this study. Previous Work j The single largest study on the surface soils of the Los Angeles region was undertaken by the Department of Agri culture in their "Soil Survey of the Los Angeles Area, I ICalifornia" (Nelson and others, 1919); a study concerned jwith agricultural description and nomenclature. Soils were i Iclassified according to their degree of tillage, moisture jretention, color, and crop growth, among other things. i i The ground water geology of the area was x ’orted by jPoland, Garrett, and Sinnott (1959) and by Thoma. (1961). j Woodring, Bramlette, and Kew allot a brief section to i the area bordering the Palos Verdes Hills in Geological Survey Professional Paper 207 (1946). The geology of the jnonmarine terrace cover and of the Upper Pleistocene Palos Verdes Formation as reported by these authors is further jelaborated by the writer. Other workers who have contributed much to unravelling the geologic history of the general area were Mendenhall (1906), Tieje (1926), and Eckis (1934). Field Methods Data obtained from approximately 400 borings were used : :in the study. Driven cores and bag samples were obtained of jthe adobe clays and underlying sediments so that evaluation l J icould be undertaken on the basis of mechanical and statis- i 1 tical analyses. 1 | Mapping of the adobe soils was done on a road map at a j scale of 3 inches equals 2 miles, issued by the Southern j I | California Automobile Club. These data were transferred to j i a base map, scale 1 inch equals 2 miles (Plate II). Mapping! jof the adobe soil was started in 1955. Because many areas have been subsequently filled, some of the soil contacts as shown on Plate II no longer can be discerned at the surface.: I ; |The accompanying geologic map (Plate III), which utilizes i jthe same scale as the soil map, was adapted from published j geologic maps by Woodring, Bramlette, and Kew (1946) and by jThomas (1961), as well as by the writer's own reconnaissance i of the area. Much of the writer's mapping was done on the basis of data obtained from borings. Acknowledgments The writer is grateful to Dr. R. Stone, head of the t- i jgraduate committee, for the numerous suggestions and helpful i jcriticisms made throughout the course of the investigation. i : The cooperation and help of the other members of the com mittee, Dr. R. Merriam, Dr. G. Chilingar, and Dr. D. Gors- j i iline is heartily appreciated. j I _ ' j Laboratory facilities of Pacific Soils Engineering, j Inc. were used for the sediment analyses. Also, much ana lytical data were obtained from engineering reports fur- j nished by this organization. X-ray diffractions were per formed by the Geophysical Institute, University of Califor- j ■ ■ i j nia at Los Angeles. Numerous conversations with members ofJ jthe Los Angeles County Flood Control District, notably Mr. ! ] I I | a . Keene, contributed much in the delineation of the Recent I geologic history of the El Segundo Sand Hills. Upper ! Pleistocene subsurface samples from water injection wells ! jwere donated by this organization for X-ray studies. Fur- ! i jthermore, well logs were made available so that cross- j i 9 ; jsections could be drawn and presented as part of this re port. Upper Pleistocene megafossils collected by the writer jwere identified by Mr. G. P. Kanalcoff of the Los Angeles j j | 1 ’ i County Museum. j i Approach to Problem | In order to delineate the relationships of the Upper Pleistocene and Recent sediments as well as the soils to the ;Quaternary history of the area, it is necessary to elaborate on the physiography which is intimately related to the geo logic agents responsible for the sedimentary features. jFurthermore, the stratigraphic relationship of the Upper j Pleistocene sediments to the Recent deposits must be evalu ated before the Quaternary history can be developed. PHYSIOGRAPHY j I | General Features ! | | The area of study is in the Angeles portion of the jPacific Border geomorphic province (Fenneman, 1931). I The dominant land form features of the southwestern portion of Los Angeles County (Plate I) include a central ! jlowland plain, the Torrance Plain; a bordering highland on i [the south, the Palos Verdes Hills; and on the east and north f f «a succession of low hills trending northwesterly which are i the surface expression of the Newport-Inglewood Uplift. i jBordering the plain on the west is an elongate coastal belt i I jof dunes and sand hills. ' i Palos Verdes Hills I The Palos Verdes Hills are an uplifted fault block | projecting peninsula-like into the Pacific Ocean in the portion of the area of study. In the main, the tills are comprised of a basement complex, the Franciscan (?) schist, upon which lap sediments of Tertiary and Quaternary age. southwest 9 j 10 j | The' highest elevation in the Palos Verdes Hills is 1480 |feet at San Pedro Hill. Below this elevation are 13 wave- icut terraces at altitudes of approximately 100 to 1300 feet f i j(Woodring and others, 1946, p. 113-116). I i j The oldest rocks exposed in the hills are Franciscan |(?) quartz-sericite, quartz-talc and quartz-glaucophane | ^schists of probable Jurassic age. I i j Miocene sediments, which are assigned to the Monterey ! ■Formation, are divided into 3 members: the Altamira Shale, j ! | Ithe Valmonte Diatomite, and the Malaga Mudstone. The Alta- j i i i mira is characterized by the abundance of silty, cherty, | and phosphatic shales; thin beds of limestone are also j [characteristic of this member. Within this member are in- I icluded the bentonitic Portuguese Tuff and the pumiceous i ; I Miraleste Tuff. The Valmonte consists mainly of diatomite j j and diatomaceous shale; whereas the Malaga is principally I comprised of radiolarian mudstone. Furthermore, basaltic intrusions consisting of chlorite and labradorite-rich i jbasalt or diabase (Macdonald, 1939) occur within the Alta- i ! mira member. Pliocene and Pleistocene sediments, consisting pre dominantly of sands, silts, and marls, lap onto the Miocene jrocks along the northeastern and eastern periphery of the jhills. < Adobe soils overlie the bedrock surface. This soil does not overlie the Pliocene and Pleistocene sediments. However, where the marine terraces are floored by beach j ! deposits comprised of flat-lying stratified gravels, pebble ] ito cobble size, there is a cover of adobe soil. Further- ! ! ; more, those terraces that are floored with rubble or are I i developed on bedrock also display an adobe soil cover. j Those terraces in the northern and northeastern portion of ' ! ithe hills which are overlain by Pleistocene deposits do not i ! j ^contain a residual adobe soil cover nor does the evidence ■ i ’ [ as presented further in the text indicate that adobe soils j lever formed on these sediments. j i ] j Newport-Inglewood, Uplift j j i — | The Newport-Inglewood deformation is topographically ' " i expressed as a discontinuous series of low hills that ex tend from the Santa Monica Mountains near the city of | Beverly Hills southeasterly into Orange County. This belt i j jis broken by the Ballona and Dominguez Gaps; the former is jone of the ancestral outlets of the Los Angeles River. 12 Baldwin Hills i j I The Baldwin Hills, with a relief of 513 feet above sea j I level, lie south of Ballona Gap in the northern portion of | j | ! i ithe area of study. Sediments comprising the hills consist j i j i ; j primarily of sands and silts of Pliocene and Pleistocene age that have been considerably faulted and folded. Dark ; i gray (10 YR 3/1) (Munsell Soil Color Charts) adobe soils : cover most of the topographic highs as well as the northern j slopes of the hills. The north flank is deeply incised; thej south flank slopes gently southward towards the Rosecrans j ' i Hills and Torrance Plain. j i Rosecrans Hills | ! i Extending southeasterly from near the city of Inglewood and to Dominguez Hill, the Rosecrans Hills form an irregular! I i I low swell about 8 miles long and 3 miles wide whose crestal j altitude ranges from 240 to 100 feet in elevation, decreas ing in a southeastern direction. Its surface is underlain by Upper Pleistocene sediments which dip to the southwest toward the Torrance Plain and in all probability merge with the Pleistocene sediments of this plain. j The swell is of deformational origin. The western i 13 ! jslope is steeper and is modified by two prominent fault 'escarpments, about 50 feet in height, which trend northwest. j j ] Black (10 YR 2/1) adobe soils cover most of the north- j :ern and central portions of the hills. The southern portionj presumably was covered by this soil which was subsequently j i | removed by erosion. j Dominguez Hill i * 1 Dominguez Hill, an elliptical dome with a northwest- southeast trending axis, is about 3 miles long and displays | I I an altitude of 195 feet above sea level. It is deformation-j ; I al in origin and like the Rosecrans Hills displays a flatterj i northeastern flank. On the west and north the hill grades 1 i I into the Torrance Plain and Rosecrans Hills. The topo graphy is only slightly modified by erosion except for a deeply incised gully on the east flank and modification of the southeast portion by the Los Angeles River. The crest of the hill is capped with adobe soil of minor areal extent which is reddish (10 R 3/4) in color and | reflects the color of the underlying Upper Pleistocene i i jsediments. | El Secrundo Sand Hills | ! The El Segundo Sand Hills extend south from Ballona i Escarpment for a distance of about 11 miles to the Palos I i I j jVerdes Hills and inland from the Pacific Ocean in a strip | • i 3 to 6 miles wide to overlap the Torrance Plain. The sand | ' ! j \ hills are comprised of a narrow strip up to one-half mile ; I I in width consisting of active dunes with an elevation of j j i ’ 185 feet above sea level and a strip from 2 to 5 miles in i width of stabilized dunes and parallel ridges and aligned ; hills. | A thin layer of soil consisting of weathered sand is : i poorly developed in places on the surface of the active dunej i belt. An "A" and "B" soil horizon, however, is well devel- j oped on the older dune sands. I Torrance Plain j i The Torrance Plain is approximately 16 miles long in a (northwest-southeast direction and 8 miles wide at its widest Ipoint. All of the topographic highs described above sur- j jround this low-lying area. Local highs in the Hawthorne iarea and in the southern portion of the Plain protrude (through this low area. i __ 15 Most of the Torrance Plain is floored with adobe soil which ranges in thickness from 6 inches to as much as 15 •feet. The greatest thickness is in the northern portion in i the vicinity of Hawthorne. Immediately southwest of Haw- i i ithorne, a constriction of the ground surface adobe occurs; jthat is, there is a narrowing of lateral extent of this deposit. j Gaps ! BaIlona Gap : ! Ballona Gap, at the northern extremity of the El I Segundo Sand Hills, is about 1.2 miles wide at its narrowest ipoint and about 10 miles long and extends from the easterly 'end of the Baldwin Hills to Santa Monica Bay. Stream-cut cliffs along the north edge of the Baldwin Hills are about i 400 feet high. The gap is floored with Recent alluvial deposits. Adobe soils (10 YR 2/1) cover most of the gap i jsurface. ! | i Dominguez Gap Dominguez Gap on the eastern side of Dominguez Hill is approximately 7 miles long and 1.5 miles wide at its 16 narrowest point. According to Poland and others (1959, p. 19), the gap was formed by an ancestral San Gabriel River i iwhich had a southward-flowing ancestral Los Angeles River L i jas a tributary. The course of the present Los Angeles River ^occupies the gap. Along the east face of Dominguez -Hill a I jstream-cut bluff is about 100 feet high. The gap is floored with Recent alluvial deposits. Adobe soils are not exposed j Iwithin the confines of the gap nor have they been encoun- j itered at depth. ! STRATIGRAPHY j I Pleistocene Series j 1 i t General Features Deposits of Pleistocene age underlie the Newport- Inglewood belt of hills, the Torrance and Ocean Park Plains i land lap onto the flanks of the Palos Verdes Hills. These i [deposits are overlain by alluvium, which although of Recent jage, was deposited at different times during this epoch. I Along the coast, the Pleistocene sediments are overlain by iRecent beach and dune deposits. The Pleistocene deposits |are primarily unconsolidated and consist of interbedded and linterfingering lenses of gravels, sands, silts, and clays. IThey include, from youngest to oldest, the Upper Pleistocene jpalos Verdes Sand, a sequence of unnamed Pleistocene depos- i iits, and the San Pedro Formation of Lower Pleistocene age. Deposits of Middle Pleistocene age do not occur within the area of study. | From well logs, the Pleistocene sediments along the I I 17 18 jcoast range from about 60 to 560 feet in thickness and as I I j ; much as 1200 feet in the Gardena Syncline southwest of | | (Dominguez Hill. According to Driver (1943, p. 308), the Pleistocene rocks in the Baldwin Hills vary from 80 to 200 feet in thickness. In the Potrero oil field, Willis and j ! j jBallantyne (1943) report the thickness of the Pleistocene ! 1 I (deposits to be 850 feet. Up to 1000 feet of Pleistocene i i I 'deposits are known to occur on the Torrance and Wilmington ! (anticlines (Davis, 1943; Winterburn, 1943). Further inland,! underlying the Downey Plain, Poland and others (19 59) stated that these deposits attain a maximum thickness of about 300C ■feet and thin northward and northeastward toward the inland ! hills. i I ! ! : j Palos Verdes Sand j This stratigraphic unit was defined by Woodring and j others (1946, p. 56) to embrace those marine deposits oc- jcurring on the youngest or first terrace of the Palos Verdes Hills. The terraces are well developed on the leeward side i jof the hills in San Pedro and along the northeasterly peri- jphery of the hills. The authors described the typical (characteristics of the Palos Verdes sand as follows: i I i The Palos Verdes sand like the older marine terrace ; 19 deposits, consists of a thin veneer on the terrace plat- j ; form, which levels formations ranging in age from Lower | Pleistocene to Miocene. Also like the older marine | terrace deposits, the strata consist generally of coarse grained sand and gravel but include silty sand and silt. Limestone cobbles are the prevailing constituent of the gravel, but granitic and schist pebbles being locally | abundant. The thickness of the Palos Verdes generally ranges from a few inches to 15 feet and is usually less j j than 10 feet. At places it consists of thin lenses, and j at other places is absent. ! I i ; \ jNorth border of the hills i I i j ! j : Excavations made for housing developments locally have ! i i i I jexposed much of the Palos Verdes Sand and its thickness is | : j jnuch greater than heretofore believed. Along the north j i i border of the hills adjacent to the Hawthorne Avenue i ■approximately 1000 feet southwest of Newton Street deformed i strata dipping 20-23° northeastward and as much as 65 feet | thick, are exposed unconformably overlying the San Pedro | I Formation of Lower Pleistocene age. The exposed section consists of a lower limestone cobble gravel bed about 24 : . j ifeet thick overlain by a 20-foot thick, brownish olive-gray friedium-grained sand containing a fossil horizon from which i | numerous specimens of Donax gouldii. Tivela stultorum and Transenella tantilla were collected. Overlying the sands are cobble gravels approximately 20 feet thick which are lithologically similar to the lower gravels. The upper ; 2o i gravels are in turn overlain by reddish-brown, iron-stained, j Ipartially cemented sands about 5-8 feet thick which are a part of the terrace cover of Recent age. t | Cuts recently excavated along Paseo de las Tortugas i ■ I 'in Torrance exposed a cobble bed 40 feet thick containing j I I ‘ limestone, schist and granitic clasts with thin stringers | |of olive-gray medium-grained sand from which several speci- t i mens of Trochycardium procerum and Nassarius perpinguis were ; i jcollected. The total thickness of the gravel bed which is | jassigned to the Palos Verdes Sand could not be ascertained j ’ ! because of residential landscaping. ! i I | | iGaffey Anticline I The Palos Verdes Sand is represented by several fossil I localities encountered in borings on the north flank of the j i ; j iGaffey Anticline. Other fossil localities, reported by j 1 j Woodring and others (1946) for the Palos Verdes Sand, are in close proximity to those encountered by the writer. i A boring immediately north of Palos Verdes Drive North at the southerly extension of Senator Avenue in Harbor City (locality 1006) encountered 18 feet of non-fossiliferous jolive-gray silt and brownish-gray sandy silt overlying 8 i feet of brownish-gray coarse-grained sand containing j 21 specimens of Anomia peruviana, , Ostrea lurida. and Dendraster excentricus resting un conformably on grayish-brown medium- grained San Pedro Sand. ! | At fossil locality 1004, 50 feet south of Pacific Coast 'Highway and 1075 feet west of Figueroa Street," 26 feet of i I ■ i slight gray to tan silt and silty clay overlying a 4 feet j thick grayish-brown medium sand containing specimens of i Anomia peruviana. Chione gnidia and fragments of Dendraster j iwere encountered in a boring. In another boring, 1400 feet ! north of Anaheim Street and 1600 feet west of Frigate Ave- j : ’ i j nue, a similar sequence was noted. j ; . i The Palos Verdes Sand containing these Late Pleistocene ifossils is folded, forming the north flank of the Gaffey } | Anticline. Therefore, it is concluded that the Gaffey : I i structure came into existence in post-Late Pleistocene time,! i probably in the early Recent. j I ^Baldwin Hills area i | Outside the Palos Verdes Hills, the San Pedro Sand or its stratigraphic equivalent has been identified in several localities within or in close proximity to the study area. j i 1. A section of massive grayish-green, very coarse i | to gravelly quartzose and loosely cemented sands noted in an excavation for the Los Angeles Outfall Sewer on the northeast side of the Baldwin Hills were assigned to the Palos Verdes Sand by Tieje (1926, p. 502-503) on the basis of the contained fauna. Although no faunal list accompanies the paper, Dendraster excentricus is cited as being j indicative of an Upper Pleistocene age for the j sediments. i i About 2 miles northeast of Playa del Rey at the i Ballona Escarpment along the west side of Lincoln j i i | Boulevard, a 10 foot thick sequence of reddish- j brown, locally cemented sand is underlain by about j 10 feet of clay, which in turn is underlain by 15 j | feet of medium-to-coarse-grained brown gravelly j sand of which the lower 6 feet contains an abundant] j | molluscan fauna. Willet (1937, p. 379-406) corre lated the enclosing sand and gravels as the strati- graphic equivalent of Tieje's Palos Verdes Sand in the Baldwin Hills. About 20 feet of light brown sand, presumably the San Pedro Formation, is ex posed below the Palos Verdes Sand. A late Pleistocene fauna has been reported by Rodda (1957) from the Cheviot Hills which are along 23 the Newport-Inglewood Uplift. The Lower Pleisto cene Anchor Silt which consists of 60 feet of soft buff silts is faunally and lithologically similar to parts of the San Pedro Sand and Timms Point Silt at San Pedro as well as the Inglewood Formation of ! | Lower Pleistocene age in the Baldwin Hills. The j Anchor Silt is unconformably overlain by the Upper : j Pleistocene Medill Sand consisting of 60 feet of i E grayish-green, loosely consolidated sand and gravel which contains a Cerithidea californica— Ostrea j l ! lurida fauna correlative of the Centinela gravel | of Willet, cited above. An Ostrea lurida fauna similar to that of the j Cheviot Hills is exposed near Palms. It occurs in a dark reddish-brown sandy silt about 10 feet below I ground surface in a cut on the west side of Over land Avenue at the north edge of Ballona Gap. According to Woodring (Hoots, 1931, p. 121) the faunal evidence indicates the enclosing sediments are of Palos Verdes age. lArea north of the Palos iVerdes Hills i i ! | The writer has mapped sediments containing fauna indi- J cative of a Palos Verdes age between the Palos Verdes Hills j ! ■ ! land those localities cited above. Several of the fossil j I I | | ^localities are from artificial cuts,* others from borings. iThese molluscan faunas occur in sediments that have been : | jpreviously reported in the literature as "nonmarine terrace j I i jcover." A faunal list and locality occurrence is presented] | ■ | ]in Table 1. j About 200 feet south of the intersection of Sepulveda j j on the west side of Vermont (locality 1000), a thin bed of j I j :grayish-green medium-grained sand beneath 10 feet of red- jdish-brown, partially cemented sand contains a molluscan i fauna indicative of Palos Verdes age. The fauna contains i j ithe typical Anomia assemblage of the Palos Verdes Sand on ]the Gaffey Anticline. j A stratigraphic break is not discernable above the ]fossil horizon within the reddish-brown sands. Heavy min- eral analyses were performed on a sample of sand collected below the fossil bed and of the "B" zone soil developed on the reddish-brown sands to determine whether these deposits reflected different provenances. The data are presented in 25 TABLE 1 FAUNA IN SEDIMENTS EQUIVALENT TO PALOS VERDES AGE Locality Species 1000 1002 1006 1007 Anomia peruviana A C A Chalamvs circulata c A Chione crnidia R R Crucibulum sninosura C R Dendraster excentricus C C C Diodora inaequalis R Donax californica C R Diplodonia p.arilis A C Epitonium cooperi R o r ' R Macoma pacis R Nassarius teaula A A Olivella baetica R R Ostrea lurida R C C Senele pulchra C Taaelus subteres A c A Teaula lioulata R C Tellina salmonea R R R Terebra pedroana R R Trachv.cardtum procerum C C A Abundant C Common R Rare |Table 2 and there appears to be very little difference in [ the heavy mineral composition of the two samples. In the ! I light fraction, an appreciable difference in feldspar con- i Itent is noted; the sand below the fossil bed contains 50 j I I ; I ' | I Iper cent feldspar whereas the soil contains 10 per cent. ; | ] I i This would be expected as the feldspars within the soil j : would weather to a clay. Based on the evidence, it is con- I i I I - i jcluded that the reddish-brown sands are not part of a ter- i i irace cover but represent the weathered upper portion of the ! | j [Late Pleistocene deposits. | ! i A greenish-gray sand approximately 18 inches thick is \ Sexposed along the bottom of a stream channel issuing from ! ! j jLaguna Dominguez at the northeast corner of Artesia Boule- ; vard and Vermont Avenue (locality 1002). A few specimens iof gastropods, Epitonium cooperi and Tecula liqulata. and a i : pelecypod, Tellina salmonea. were collected from this sand } j |and thus a Palos Verdes age is indicated. The same fossils occur in the Anomia fauna of locality 1000. I The typical Anomia fauna of the Palos Verdes Sand on 1 the Gaffey Anticline was collected from a greenish-gray medium-grained sand at the ground surface. This locality (1003), in a stream channel at the northwest corner of President and Senator Avenues in Harbor City, has since been TABLE 2 HEAVY MINERAL ANALYSIS Mineral Locality: 1000 Locality: 1001 "B" Horizon Soil Sand* "B" Horizon Soil Sand* Magnetite 3 % 3 % 3% 3 % Hornblende 66 60 57 55 Epidote 38 42 34 37 Garnet 1 — — 1 Hematite 5 2 4 3 Tourmaline 5 1 — 1 Apatite 2 — 2 2 *Sand immediately below fossil horizon covered with man-made fill. A comparable fauna was noted at [locality 1009 in a similar enclosing sand bed in a stream channel that existed prior to residential development at i [what is now the intersection of New Hampshire Avenue and | '210th Street in the Carson area of Los Angeles County. j : i At locality 1007 at the northeast corner of Sepulveda t i jBoulevard and Figueroa Avenue, an Anomia— Ostrea fauna was [ I i Icollected from a recently excavated cut. The fauna occurs i within a yellowish-gray, medium- to coarse-grained sand bed ! ! . I |3 feet thick which is overlain by a greenish-gray clay bed j japproximately 1.5 feet thick which in turn is overlain by : ! | adobe soil. Along with the molluscs, a horse tooth, Equus j ; _ i sp., and mammoth bone fragments were also collected. Between localities 1007 and 1009, a boring west of ! I i i [Vermont approximately .25 mile north of 223rd Street (local-! ity 1001) encountered 15 feet of non-fossiliferous buff sand overlying a greenish-gray, medium-grained sand 5 feet thick I [containing a few specimens of Anomia peruviana. Heavy min- | 'eral analyses were conducted on a sample of sand underlying i the fossil horizon and of the "B" zone soil. Data are pre sented in Table 2. There is close correlation of the heavy mineral composition of these samples compared with those of i jlocality 1000. | Two identifiable specimens of Cerithidea californica | j ialong with finely comminuted shell fragments were noted in i jdrill cuttings from a greenish-gray sand bed at 20 feet in I i jdepth (locality 1011) at the southwest corner of Imperial j i Highway and Dalerose Avenue. This locality marks the most j J. i : 1 I I northern extent of fossils indicative of a Palos Verdes age \ i collected by the writer in the Torrance Plain. ; j ! i Sediments of Palos Verdes age are represented on the ! i I Rosecrans Hills by 3 specimens of Anomia peruviana from a j boring (locality 1010) approximately 1000 feet northeast of j ; i i j [Florence Avenue and Hyde Park Boulevard. The enclosing 1 i i ! greenish-gray medium-grained sand 8 feet thick is overlain ! | by 34 feet of non-fossiliferous buff, fine-grained sand and [silt. j ! . | i j On the west flank of Dominguez Hill near the intersec- j I i ■ I tion of Victoria Street and Avalon Boulevard, Poland and others (1959, p. 36) reported that a marine shell zone 20 ito 30 feet below the ground surface was encountered in water | well 3/13-32F6. Although no faunal list accompanies the report, the authors stated that the shell zone represents the Palos Verdes Sand. Fossils representative of a Palos Verdes age, Anomia peruviana and Ostrea lurida. were noted in a grayish-green fine-grained sand 24 feet below ground level in a boring about 300 feet southeast of the cited well, j In the Redondo Beach area, injection well 9M (locality jl005) of the Los Angeles County Flood Control District en- l I jcountered a marine shell horizon occurring in a grayish- i ! j j green coarse-grained sand at 120 to 130 feet below the land j I ! Ssurface. Specimens of Dendraster excentricus. Nassarius i i i > jperpinguis. Olivella baetica_. and Anomia peruviana indicate ja Palos Verdes age for this sand horizon. The sand horizon ! ! ; i |is overlain by 20 feet of brownish-gray clay which in turn ; i ! f jis unconformably overlain by approximately 100 feet of olderj | '* j dune sand. In injection well 8T, 4500 feet northerly of thej I * aforementioned well, the same fossil horizon occurs at 140 J i ; i j Ifeet below ground surface. The enclosing tan fine-grained ! ! ! | j |sand is overlain by 10 feet of beach deposits, coarse grained sands and gravels, which in turn are overlain by 70 Ifeet of older dune sand. lstratigraphic__relationships ; From the foregoing, it can be said with certainty that the depressed surface between the Palos Verdes and Baldwin Hills southwest of the Newport-Inglewood belt of hills is underlain by sediments of Palos Verdes age as indicated by the contained fauna. Furthermore, the enclosing sand 31 horizon can be traced laterally, albeit at depth, over a large portion of this area. The upper surface of the Palos | Verdes Sand, approximately 0-50 feet above sea level, is eroded and irregular and appears to dip seaward, to the | southwest, at approximately 8°. j | | Wissler (1943) subdivided the Los Angeles Basin Pleis- ! i i tocene section of the basin oil fields into two parts, the I Lower Pleistocene and Upper Pleistocene. The Lower Pleis- i - i jtocene strata were correlated with the San Pedro Formation, j i I ; \ jthe Lomita Marl, Timms Point Silt, and San Pedro Sand, of | the Palos Verdes Hills. The Upper Pleistocene was differ- i i entiated on the basis of a lignite zone at the base and in- j i I jcluded the Palos Verdes Sand. Those deposits occurring on I ! I t the youngest terrace of the Palos Verdes Hills, the Palos Verdes Sand, are shoreline deposits representative of the j I i thick sequence of sediments within the basin deposited dur- j jing the Upper Pleistocene. As defined by Woodring and i bthers (1946, p. 56), the Palos Verdes Sand is restricted j to those deposits occurring on the youngest terrace and, therefore, its designation cannot be applied to those Upper Pleistocene deposits occurring within the area of study. Unnamed Upper Pleistocene Deposits In agreement with Poland and others (1959), the strata of Late Pleistocene age which underlie the study area be tween definite correlations of the Palos Verdes Sand above | I I i I jand the San Pedro Formation below are termed "unnamed Upper j i ! i : '.Pleistocene deposits." These sediments extend as far north; i j i jas the Ballona Escarpment and southerly to the Palos Verdes j [Hills. Between these limits they extend from the coast ! j ■over the crest of the Newport-Inglewood belt of hills, in land beneath the Downey Plain, forming a blanket deposit throughout much of the Los Angeles Basin. Nowhere within the area of study are these deposits totally exposed. They are known from water or oil wells and borings that penetrate the San Pedro Formation of Lower j Pleistocene age. Physical Character The unnamed Upper Pleistocene deposits vary in lithol- ogy both vertically and laterally. They represent shallow lagoonal, tidal or near shore deposits derived from varying source areas and were deposited under rapidly changing con ditions . The upper portion of the deposits are mainly i L_ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ fine-grained, consisting of sand, silt, and clay, whereas : j |the lower part is predominantly sand containing some gravel and subordinate amounts of clay and silt. j The basal or lowest member of the unnamed Upper Pleis- j i j jtocene deposits is a productive aquifer in much of the ! I ! ! i ilnglewood-Torrance area. It was designated the "200-foot i i jsand" by Poland and others (1959) because its midposition is i japproximately 200 feet below the ground surface in the jGardena Syncline extending through Gardena northwest to ! i ] ! ' ! | Inglewood. | i I Although this unit is comprised mainly of sand, its j composition is variable. Well logs indicate that the "200- j j i ifoot sand" underlying portions of El Segundo and Gardena is | j ; largely gravel. In the southeastern portion of the study area near Dominguez Gap the lithology is a fine sand. Along , i i the coast, the "200-foot sand" is represented by the Redondo i ;Tight Zone, a deposit of variable thickness that is com- iprised of clays and silts which overlie the San Pedro For- j mation (Plate IV). In the Redondo Beach area, a coarse sand and gravel, the Merged Silverado Zone, overlies the Redondo Tight Zone. Along the coast extending from the Palos Verdes Hills northward to Manhattan Beach, the upper member of the junnamed Upper Pleistocene deposits is represented by the j i j Manhattan Beach Aquiclude, a brownish-gray clay whose thick-| ness varies from 10 to 40 feet. Well logs indicate this j clay cap to consist of discontinuous lenses intercolated |with coarse-grained sands and gravels. I ! I ' It was thought that the upper surface of the clay cap Imight represent a buried soil horizon and if so would aid i i ! jin dating of the overlying sediments. Thus, X-ray analyses | jof clay samples obtained from this deposit were performed. i | j(The techniques used in the X-ray diffraction study are presented in the sedimentary analyses section of the text.) j i j ; Results of the X-ray study (Table 3) indicate that the clay | icap consists of such minerals as illite, chlorite and mont- j i • i jmorillonite and therefore is a marine deposit and not a | I ; i I jburied soil. Marine environmental conditions favor the formation of montmorillonite, illite or chlorite clay min- ; | erals because sea water is alkaline and contains appreciable [dissolved calcium, and because there is no leaching. Fur- i thermore, diagenesis of chlorite clays can only occur in a marine or lacustrine environment (Grim, 1953). Thickness Thickness of the unnamed Upper Pleistocene deposits TABLE 3 X-RAY DIFFRACTION DATA— MANHATTAN BEACH CLAY CAP Well Number Depth {ft.) Age Predominant Clay Mineral Other Clay Minerals Non-Clay Minerals 8K 110 Upper Pleist. I K F, Q 9D 100 Upper Pleist. M I Q 9J 109 Upper Pleist. C I, K F, Q 9T 137 Upper Pleist. M H O Q, F 9V 176 Upper Pleist. M I, K, C Q, F M Montmori1Ionite K Kaolinite I Illite F Feldspar C Chlorite Q Quartz i V LO U1 I 36 jvaries from 60 to 560 feet. The approximate thickness and [depth of these deposits (Table 4) indicate that the Man- j hattan Beach Clay cap and the Redondo Tight Zone are not jpresent along the axis of the Gardena Syncline or at least j : I they have not been identified. j ' i ! | Stratigraphic Relationships j i Wissler (1943) reported that oil wells on the Dominguez •Hill encounter nonmarine sands, clays and gravels to 175 j ' i ifeet below the ground surface. These are underlain by lagoonal deposits about 40 feet thick. A thin bed of lig nite and about 300 feet of marine sand and gravel underlie [ the lagoonal deposits. It includes a megafossil zone, San Pedro in age, from 215 to 250 feet below the ground surface. i Wissler assigned the lagoonal deposits and the marine sand j and gravel to the San Pedro Formation; the nonmarine section to the Upper Pleistocene. The upper 25 feet of this section [is marine and of Palos Verdes age as indicated by the Anomia | [fauna collected by the writer. Whether the remainder of the j i Upper Pleistocene deposits are marine cannot be definitely stated because of the absence of fossils. Along the coast, the Manhattan Beach Aquiclude is of marine origin. It cannot be stated with certainty that the TABLE 4 THICKNESS OF THE UNNAMED UPPER PLEISTOCENE DEPOSITS Deposits Along the Coast *Along Axis of Gardena Syncline Thickness of unnamed Upper Pleistocene Deposits 60-560 ft. 180-280 ft. Thickness of "200-foot Sand" 65-135 ft. Thickness of Manhattan Beach Aquiclude 0-130 ft. Thickness of Redondo Tight Zone 20-220 ft. Depth to base below ground surface 140-700 ft. 240-310 ft. Altitude of base below sea level 75-570 ft. 65-135 ft. *After Poland and others (1959). underlying coarse sands and gravels which are considered to jbe in part the stratigraphic equivalent of the "200-foot JSand" are of marine origin because of the lack of fossils. j jWithin the Redondo Tight Zone, brackish water foraminifera [represented by Cassidulina limbata. Uviuerina iuncea. Boli- Ivina spissa and Elphidium sp. are common. A marine origin jis indicated for this unit. From the foregoing, the Upper Pleistocene deposits are Ithus inferred to be partly of marine and partly of contin- jental origin. Injection wells along the coast encounter a jsimilar stratigraphic sequence as reported by Wissler for the marine San Pedro Formation below the base of the unnamed Upper Pleistocene of Dominguez Hills. A lignitic horizon I I I land lagoonal deposits, exemplified by streaks of organic i j matter within clayey gravels, and a marine sand section jincluding a megafossil zone at 335 feet below the ground .surface underlie the Redondo Tight Zone. The contact between the unnamed Upper Pleistocene de posits and the underlying San Pedro Formation in the area of study is not exposed. Well log data are insufficient to supply the stratigraphic relationship. Presumably, the contact would be unconformable along the Newport-Inglewood Uplift. Along the coast, the existence of a lignitic 39 horizon and lagoonal deposits suggests that at least local ly , the contact would be unconformable. It appears likely, however, that the unnamed deposits are conformable on the t jSan Pedro Formation along the synclinal axis of the Gardena j jSyncline. \ j Thomas (1961, p. 56) included all Upper Pleistocene deposits older than the Older Dune Sand in the Lakewood Formation. Its designation was selected from a typical section indicated in a log of a water well at Lakewood. Here, the Upper Pleistocene section attains a maximum thick ness of 340 feet. Included in the Lakewood Formation are Terrace Deposits, Palos Verdes Sand and the unnamed Upper Pleistocene deposits as well as the Gardena Aquifer. As I j will be shown in the text, the Gardena Aquifer is Early Recent in age and the Terrace Deposits span a time interval i from Upper Pleistocene to Recent. There are 13 marine terraces ranging in altitude from | jlOO to 1300 feet above sea level on the Palos Verdes Hills. t The Palos Verdes Sand was deposited on the youngest or low est of these terraces (Fig. 2). The remainder of the ter races were cut during successive periods of uplift during jthe time interval between the deposition of the San Pedro formation and the Palos Verdes Sand. Thus, the sediments, 40 Fig. 2.— Palos Verdes Sand. Pebble to boulder size, flat-lying beach gravels, 10 feet thick of the Palos Verdes Sand unconformably overlie the San Pedro Formation of Lower Pleistocene age. Beach gravels were deposited on the wave-cut platform of the youngest ter race. The San Pedro Formation strikes E-W and dips 23° north. As a result of surficial creep, adobe soil over lies the Palos Verdes Sand. View looking east from Western Avenue. 41 in part, occupying these terraces are correlative of the unnamed Upper Pleistocene deposits. Furthermore, the de formation that created the uplift is probably reflected in the coarse-grained deposits occuring in the lower part of i t the unnamed deposits. Pleistocene to Recent Series | Nonmarine Terrace Cover I iGeneral features 1 ! j [ Lawson (1893) first described and recognized 11 marine i i iterraces on the Palos Verdes Hills. Subsequently, Woodring 1 land others (1946) recognized 13 terraces. Their distribu- i | jtion, designation, and correlation are shown on Plate 22 i 1 I jof the latter reference. The numerical designation as i jused by Woodring is maintained in the present study. In- i jasmuch as a comprehensive treatment of the physiographic | features of the terraces are given by the authors, repeti tion is not warranted. Newly created exposures of the nonmarine terrace cover as well as the underlying platforms were readily accessible to the writer because of the numerous excavations for road construction and housing developments. Moreover, many of 42 the lower or younger terraces have been explored by borings. Thus, much more data are now available as to the lithology and stratigraphy of these deposits. Physical character i j t j Most of the nonmarine terrace cover is comprised of poorly sorted to unsorted rubble and crudely stratified i j jgravelly sands which either overlie marine deposits which in i |turn rest on the wave-cut platforms or overlie the platforms i i per se. The deposits represent talus, slope and rill wash, jfan detritus and landslide material which accumulated after i I [emergence of the terraces. However, in some instances the I i Irubble was deposited prior to emergence as exemplified by [ j jthe exposed deposits on the twelfth terrace at an altitude i |of approximately 1215 feet in a cut on Crest-Road. -Woodring i | land others (1949, p. 54) stated that a 2-foot interval [within the rubble contains abalone (Haliotis crocherodii) and a few turban shells (Tequla crallina) and overlies marine deposits consisting of coarse sand and gravel that contains marine shells. On the second terrace northeast of Long Point, a partially cemented mixture cf cobble to boulder size fragments of rubble and well to subrounded clasts dis playing pholad borings along with comminuted shells were 43 noted in an excavation. Thickness of the deposit ranged from 4 to 6 feet. Thus contemporaneous deposition is indi- |cated. On the tenth terrace on the southwest slope of San Pedro Hill, borings have encountered as much as 30 feet of rubble overlying a fossiliferous, marine, coarse sand, 1 jfoot thick, at about elevation 1110 feet. This is in turn junderlain by 10 feet of rubble. The fossils indicate the I i jsand horizon to be older than the Palos Verdes Sand. In jthis instance the lower section of the rubble predates the jmarine deposit. j Thickness of the nonmarine terrace cover seldom exceeds ilOO feet and the thicker portion is restricted to the cliff ;face of the wave-cut platform. Most of the cover ranges in i i ithickness from 2 to 60 feet. Thickness is usually much t jgreater on the younger terraces than on the older; the lat- | jter having lost most or practically all of the original cover through erosion. However, in places, as on the fourth terrace, exposed in a road cut north of Palos Verdes Drive South near the Marineland entrance, the terrace cover is absent. Here, the adobe soil rests directly on the plat form. On the fourth and fifth terrace east of Palos Verdes Drive West north of the intersection of Hawthorne Avenue, the rubble cover seldom exceeds 6 feet. Further north, in 44 the Margate area, as much as 55 feet of rubble has been encountered in borings on the fourth terrace. Hence, it can be readily seen that the thickness is variable and the ac cumulation was considerably greater in one area than anoth er. Moreover, the detritus comprising the cover usually reflects the lithology of those indurated sediments re- 1 jstricted to the area immediately above the site of accumu- jlation. Basalt rubble is only found where basalt crops out; [similarly with limestone. Barite occurs along two minor [fault zones that transect and predate the fourth and fifth [terraces along Palos Verdes Drive West. The rubble com prising the cover contains an appreciable amount of this mineral. ! I 1 The fifth terrace north of Palos Verdes Drive South jand west of Western Avenue has been displaced westward by a [landslide. The slide, about 25 feet thick, is comprised of I jnonmarine terrace rubble and overlies a nondisturbed terrace ! [cover about 40 feet thick. Field relationships indicate that the slide has overridden a portion of the fourth ter race. That the terrace was not developed on the slide is indicated by fragments of adobe soil that occur along the failure plane at the head of the slide. The lowest terrace along the northern periphery of the 45 hills was deformed subsequent to emergence and deposition of the nonmarine terrace c o v e r . Both the Upper Pleistocene Palos Verdes Sand and the overlying terrace cover display a jnorthward dip as much as 26°. Gaffey Canyon was developed ! ion the warped lowest terrace by an antecedent stream that I breached the Gaffey Anticline. Because deposits younger jthan the Palos Verdes Sand are involved, deformation must I ihave occurred in Early Recent times. i Most of the platforms are flat-lying or nearly so, displaying a gentle seaward dip. Presumably the surface ^represents the initial planation attitude, albeit uplift of j ithe terraces has since occurred. However, the surface of i many of the platforms in the westerly portion of the hills I j are undulatory. Because of the massive character of the jterrace cover, it cannot be said with certainty that the joverlying cover is not deformed. Furthermore, in some in- 1 ■stances where the platform is not undulatory, the surface I jdisplays a transverse dip greater than the seaward dip. Evidently, uplift was not uniform during each terrace rise. The nonmarine terrace cover has been shown by Woodring and others (1946) to encroach onto the Torrance Plain. Poland and others (1959) described the sediments capping portions of the Santa Monica-Torrance area as non-fossilif- 46 erous, probably continental, and consisting of reddish-brown sands and silty sands ranging from a few feet to about 20 feet in thickness. On the basis of fossils found within these sediments, the heretofore described terrace cover as previously mapped is of marine origin and Upper Pleistocene j jin age. Furthermore, the terrace cover that overlies the i marine terrace deposits of the youngest terrace along the ] jnortherly foothills is much unlike the rubble that covers !the older terraces. Mineralogically, a part of this terrace I t jcover is similar to the sands comprising the San Pedro For- jmation, thus indicating its source. i ! Recent Series i ! i Definition and General Features i j Reade (1872) first defined the Recent epoch as that time interval since the beginning of the last major rise in jsea level. Shepard (1956) and Hopkins (1959) have assigned | an approximate age of 15,000 years since the beginning of the Recent epoch. The deposits of Recent age comprise the youngest un consolidated sediments formed during the present cycle of alluviation, as well as deposits indicative of lagoonal and 47 littoral environments, eolian deposits, fluvial deposits and residual and transported soils. Recent deposits are recog nizable by their unconsolidated nature, relationship to the present and past drainage systems, unconformable relation- jship with the underlying Upper Pleistocene sediments, the | [presence of buried soil profiles, and development of youth- i |ful soils. i i Gardena Aquifer i peneral features i ! Richter (1950) described the coarse deposits comprising ] the Gardena Aquifer which extends inland from Redondo Beach, i jacross the Newport-Inglewood Uplift within the confines of i jthe broad saddle between the Rosecrans Hills and Dominguez j Hill to beyond the city of Lynwood (Plate V). He indicated that this aquifer is of fluvial origin because the alignment j [over the Newport-Inglewood Uplift was narrow and perpendicu lar to probable ancient shorelines. Furthermore, he stated j that the deposits comprising the aquifer are similar to those, Recent alluvial deposits in Dominguez Gap. Some an cestral river, possibly the Los Angeles River, which flowed southwest, incised a channel across the Newport-Inglewood 48 Uplift and the channel was subsequently filled with fluvial deposits. According to Thomas (1961, p. 63), the Rio Hondo- San Gabriel River systems may have been the principal transporting agent for sediments comprising the Gardena Aquifer. They further observed that because the two inland j llobes of the aquifer in the Hollywood area extend parallel ! ;to the inland foothills there is a possibility that the Los j jAngeles River may have deposited portions of it. t ! The aquifer ranges in thickness from 40 feet near ] jLynwood to 100 feet near Gardena and increases to 160 feet jnorthwest of Torrance. Contours plotted on the base of the 'aquifer indicate that Recent uplift along the crest of the Rosecrans Anticline has arched the Gardena Aquifer. Fur- i I ithermore, the aquifer is folded in the Gardena Syncline, i | vindicating this structure had its origin subsequent to the I deposition of the fluvial deposits. I I • . The fluvial sediments of the Gardena Aquifer are con sidered to be Early Recent in age because (1) the channel containing the deposits is incised into the underlying unnamed Upper Pleistocene sediments, and (2) in the Redondo Beach area, the Older Dune Sand of Recent age overlies the 49 Gardena Aquifer. Moreover, the Recent sediments of the Gardena Aquifer are older than those fluvial deposits in Ballona Gap because the overlying older dune sand that occu pied the gap was removed by the antecedent Los Angeles River. Thus, if both deposits were laid down by the same ancestral river, gap cutting was done sometime during the Recent epoch subsequent to the deposition of the Gardena [ i iAquifer . ! Redondo Canyon i The outline of Redondo Canyon as determined from the l l Coast and Geodetic Survey Map 5101 is depicted on Plate V relative to the subcrop position of the Gardena Aquifer. I I The alignment of these two features leaves little doubt that 1 the ancestral river which incised the channel that contains the Gardena Aquifer also formed Redondo Canyon. Although it cannot be said with certainty that the Gardena Aquifer ex ists off shore at the head of the canyon, it is well known that the aquifer has been subjected to salt water intrusion along the coast and thus it is inferred that these fluvial deposits are in hydrologic contact with sea water. The Los Angeles County Flood Control District initiated its West 2oast Basin Barrier Project in 1959 to prevent salt water 50 intrusion not only of the Gardena Aquifer but also the Merged Silverado Zone. Thus, it is also inferred that Upper Pleistocene deposits exist off shore and that the upper portion of the canyon is incised into these deposits. The lower portion of Redondo Canyon, however, is cut into Mio- jcene and possibly Pliocene sediments (Emery, 1960, fig. 49). I It is believed that Redondo Canyon is the product of ! jsubaerial erosion which occurred in post-Palos Verdes time jinasmuch as the landward segment of this feature is incised jinto deposits which are.the stratigraphic equivalent of the i 1 fPalos Verdes Sand. Whether uplift or lowering of sea level | lor a combination thereof exposed the Upper Pleistocene sed iments to erosion cannot be said with certainty. However, it is more plausible to believe that uplift was the most Important factor if one considers that the present depth j below sea level of the canyon is about 2000 feet. It is Ivery likely that uplift or tilting of the Upper Pleistocene t jsurface was related to movement of the Newport-Inglewood j Fault zone. The suggested origins of submarine canyons are dis cussed by Shepard (1948). 51 Older Dune Sand General features A belt of stabilized dunes, parallel ridges and aligned [hills 2 to 5 miles wide and about 12 miles long parallels i I Ithe shoreline from the Ballona Escarpment to the Palos Ver- j jdes Hills and extends inland from 3 to 6 miles to overlap I jthe Torrance Plain (Fig. 3). These sediments are also ex- | posed north of Ballona Gap and cover a portion of the Ocean Park Plain. In Ballona Gap the older dune deposits were removed by the antecedent ancestral Los Angeles River. i ! The older dune sand has been described by Poland and j jothers (1959) and by Thomas (1961). Merriam (1949) gave a f | ^'comprehensive treatment of the sand composition and mineral- I j ;ogy as well as characteristic sedimentary features of this deposit. i i j Thickness and physical character The older dune sands and other sediments which comprise the El Segundo Sand Hills are no thicker than 150 feet and consist of fine- to medium-grained sand with minor sandy silt, clay, and gravel lenses. These deposits can be Fig. 3.— El Segundo Sand Hills. Active dunes appear as the light colored belt along the coast. Older sand dunes on the landward side. View looking south. Photo graph by Pacific Air (1947). u i ro 53 divided into 3 lithologic units: (1) a deeply weathered and partially cemented dune sand extending to about 20 feet in depth, underlain by noncemented dune sand consisting of medium-grained, compact, and clean sands; (2) an intermedi ate zone of terrace deposits; and (3) a lower horizon con sisting of beach gravels and coarse sands. I The upper portion of the dune sand is comprised of dark ! i r eddish-brown (10 R 3/4} to yellow-brown (10 YR 6/4), fine- i I ■to medium-grained, cross-bedded sands. Deep weathering has i j |oxidized the iron minerals which through leaching and cemen tation processes have partially filled the interstices be tween the mineral grains. According to Merriam (1949, p. I |27), hornblende is the most common heavy mineral, ranging from 10 to 60 per cent of the heavies. In the light frac tion, quartz varied from 60 to 80 per cent. Cross-bedding j jis of the eolian type in that the truncating planes display i I steep dips up to 40° to the planes of deposition. This is well displayed in a cut about 40 feet in height on the south side of Pacific Coast Highway near its intersection with Calle Mayor. The intermediate zone is not exposed and is known only from excavations or injection wells drilled by the Los Angeles County Flood Control District in the West Coast 54 Basin Barrier Project and from water well data of the State of California, Division of Water Resources. At a variable depth of 50 to 80 feet below the dune surface, the cross bedded, medium-grained sands give way to bedded, finer and coarser sand deposits whose colors range from yellow-brown to tan to gray. Interspersed are occasional streaks of 'lenticular white to gray silty clays less than 1 foot thick. i i jThe intermediate zone or terrace deposit represents a j transition in depositional environment from the underlying jbeach deposits and the overlying dune sands. ; The beach deposits are for the most part comprised of i !medium to coarse sands that contain abundant mica flakes. I llnterbedded layers and lenses of multicolored gravels, s jgranule to pebble size, along with shell and wood fragments !make up the remainder of the deposit. Its thickness is ivariable and well logs indicate a range of 25 to 70 feet. Well log data and exposures show these zones are not continuous along the coast. In Ballona Gap the older dune sands rest directly upon the Palos Verdes Sand. In the Hermosa Beach area, the older dune sands rest on the clays of the Manhattan Beach Aquiclude. Furthermore, the older dune sands directly overlie the youngest nonmarine terrace cover in the Palos Verdes Hills. Beach sands and gravels 55 overlie and transgress the fluvial deposits of the Gardena | Aquifer. i I jOricrin I i | j According to Poland and others (1959) and Eckis (1934), [the parallel ridges and aligned hills are interpreted as ‘ offshore bars modified by wind and stream action since their emergence from the sea and that the bar deposits were prob- j I ably formed during a high level of the seas immediately ! prior to the latest Pleistocene withdrawal. If these de posits are indeed offshore bars, then one would expect lagoonal deposits to be present inland and adjacent to the I hills. Well logs show this is not the case. i j 1 Lowering of sea level undoubtedly exposed the beach i Sands to the action of the wind resulting in the formation of the older dune sand. ! i Age i, A Recent age is indicated for the older dune sand based on its stratigraphic position relative to the first non marine terrace cover. At Malaga Cove, the nonmarine terrace cover is approximately 25 feet thick and is overlain by about 30 feet of older dune sand. The terrace is considered 56 to be of Late Pleistocene age (Woodring and others, 1946). Moreover, the older dune sands in Ballona Gap rest on sedi- ! ' j ments of Palos Verdes age. Inasmuch as the beach deposits underlying the older sand dunes overlie the Gardena Aquifer jwhose fluvial deposits are deposited in a channel that has [been incised into Upper Pleistocene sediments, there can be ;little doubt as to the Recent age of the older sand dunes. However, comminuted and identifiable fossils indicative of a Late Pleistocene age have been collected at several local ities occurring as pockets at the base of the older dune sand or within the intermediate zone. These fossils are 'considered to be reworked and undoubtedly were carried to i the sites of deposition by small streams that drained the ] then existing Upper Pleistocene surface. j The relationship of the overlying beach deposits to the Gardena Aquifer indicates that the time interval between the backfilling of the landward segment of Redondo Canyon jand the formation of the beach deposits was one of rising | sea level. There is no way to estimate the time lapse; at least within a portion of this interval, approximately 130 feet of fluvial deposits were deposited in the canyon along the coast. 57 Active Dune Sand I i Eolian sands occur xn a narrow strxp fringing the coast j 0.2 to 0.5 mile inland and extend from Ballona Gap southward to the city of Redondo Beach for a distance of about 9 i jmiles. These deposits are lenticular, composed of fine to i medium, white to grayish-white sands that are usually well i ‘ sorted. The dunes display a crestal altitude ranging from j i 185 to 185 feet above sea level. Thickness of the dune sand i sranges from a feather edge to as much as 70 feet. Because the wind direction is fairly constant blowing i jacross the fronting sandy beach, a long parallel ridge of j Isand has developed transverse to the prevailing wind direc- ! jtion. The dunes display a windward slope of about 10-15°; j |the leeward side is much steeper, ranging from 18° to 32°. The dune sands, which are Recent in age, overlie the older dune sands; and in places, the latter deposit pro- i jtrudes through the younger dune sand. Horizontal movement ! of the sand was computed by Merriam (1949, p. 22) to be 5 feet per year west of the dune crest. Migration of the dune sand has been halted by encroacihing residential development. That the dunes have undergone several stages of devel opment is shown by the formation of thin soil layers as 58 much as 0.5 inch thick as seen in several excavations on the windward side of the dunes. Occasionally, cut and fill of I ■the soil layers undoubtedly due to wind scour was noted. I jLateral correlation of these soil horizons was not possible j because of their limited areal extent. | ! Fifty-foot Gravel i J Iphvsical character j j At about an average depth of 50 feet near the coast I within the confines of Ballona Gap, a gravel bed approxi- j jmately 10 feet thick increasing to 40 feet in thickness I upstream is comprised of coarse sand, rounded to subrounded I Ipebbles and cobbles up to 8 inches in diameter. j ! Poland and others (1959, p. 30) termed the gravel bed ■the "50-foot gravel" and a hydrologic treatment of this ideposit is given by the authors. The deposit is also known 1 as the "Ballona Aquifer" (Thomas, 1961). As determined from well logs by Poland, the transverse profile of the base of the "50-foot gravel" west of the Baldwin Hills dips south eastward across Ballona Gap. The tilt of the gravel bed coupled with difference in chemical structure of the native waters within the underlying Lower Pleistocene San Pedro 59 Formation north and south of the gap is believed by Poland to indicate that the straight alignment of Ballona Escarp ment west of the Baldwin Hills may in part represent a fault (scarp. However, the authors stated that there is no hydro logic evidence indicating a ground water barrier along the escarpment. If the escarpment represents a fault scarp, i 'then the fault must be of Recent age; younger than the Re- I [cent older dune sands inasmuch as these sediments are ex- ( [posed in the face of the escarpment. | Bore hole data indicate a vertical offset of the gravel (bed across the Inglewood Fault. Whether this offset is due l ito faulting or due to deposition on a pre-existing irregular i i i isurface could not be ascertained. i i [origin j Pebbles and cobbles of the "50-foot gravel" are of both (granitic and metamorphic derivation. Some of the pebbles i [are composed of slate and spotted slate indicating that the I source was the Jurassic Santa Monica Formation exposed in the Santa Monica Mountains, On the other hand, the granitic pebbles and cobbles indicate that their source may have beer the San Gabriel Mountains. It is believed, however, that the granitic clasts, in part, are reworked as evidenced by the superimposed abrasion of the rounded cobbles. Their immediate source was very likely the Upper Pleistocene ter race deposits that comprise the Santa Monica Plain and the gravels were deposited by southward flowing tributary streams discharging directly into the gap. That this oc curred is evidenced by the tongue-like projections of the ! gravel bed (Plate V) . The gravel projection on the souther i i ;ly side of the gap is presumed to have been deposited by ! j fcentinela Creek. Prior to the integration of drainage by i j the Los Angeles County Flood Control District, Centinela r i Creek maintained a course parallel to the river along its j South margin and its course presumably was altered subse quent to the deposition of the gravels by the uplift that j tilted the older dune sand. j f t q e , i i I Regardless which streams accomplished the backfilling I [ pf the gravels, the older dune sand was removed by stream erosion and thus the gravels must be Recent in age and younger than the older dune sand. Because the older dune sand overlies the Gardena Aquifer, the "50-foot gravel" is younger than the aquifer. Ancestral Los Angeles River 61 Ballona Gap was presumably cut by the ancestral west ward flowing Los Angeles River into Upper Pleistocene (Palos Verdes) sediments and the gap is floored by Recent alluvial deposits from a depth of 50 feet near the coast to about 80 feet 9 miles upstream. Thus, the antecedent river reached ia level of at least 50 feet below present sea level and as i i much as 400 feet below the Upper Pleistocene surface along jthe Inglewood-Newport Uplift. Poland and others (1959) jbelieved that the existing gap represents an inland segment j ;of trenching and that the incised stream was graded to a i base level much greater than 50 feet below present sea level I |and possibly as much as 2 to 3 miles seaward from the pres- j lent coast. | The relationship of Santa Monica Canyon to the subcrop jlimits of the "50-foot gravel" as shown on Plate V indicates ! jthat the alignment of these two features are not as apparent as for Redondo Canyon and the Gardena Aquifer. However, if Ballona Gap represents an inland segment of trenching, then there is a possibility that Santa Monica Canyon may have been incised by the ancestral Los Angeles River. Detailed studies of the head of the canyon reveal the presence of 62 3 tributaries, any of which could be the ancestral Los Angeles River. Because of deposition by long shore currents and the several streams that empty into Santa Monica Bay, the area between the coast and the presently known head of the canyon has been built up and any indication of the sea- jward extension of the canyon from shore cannot be discerned. j The age of canyon incision is not as clear as that of i (Redondo Canyon. It is likely that Santa Monica Canyon was I iincised at the same time as Redondo Canyon. If not, then a I jsubsequent lowering of sea level of about 1900 feet would be required. There is no substantiating evidence to indi- i cate this event occurred even though there was a slight jlowering of sea level which exposed the beach deposits to form the older dune sand. ! It is assumed that both rivers drained the Los Angeles jBasin in Early Recent time prior to the deposition of the Gardena Aquifer. Movement probably occurred along the south portion of the Newport-Inglewood Fault zone to cause a change in stream regimen for the river that incised Redondo Canyon so that its channel was aggraded. Consequently, the ancestral Los Angeles River was the only through-flowing stream in the area of study that continued to degrade its channel. Degradation continued until the antecedent river 63 could not maintain itself through the Baldwin Hills Uplift. The river subsequently altered its course presumably to flow through Dominguez Gap and a new cycle of gap-cutting was initiated. Inception of the older dune formation is closely re- | jlated to the history of the ancestral Los Angeles River. ;Dune formation is obviously subsequent to canyon cutting. jFurthermore, the ancestral river is antecedent only in re lationship to the Baldwin Hills Uplift. The existence of | jthe older dunes as a continuous deposit across Ballona Gap jis not possible. If this were not the case, then the dunes j iwould have to have been breached after deposition. More- i [ (over, this premise suggests that the uplift of the Baldwin I Hills that caused the change in course of the ancestral Los i jAngeles River occurred prior to the dune formation. There- | jfore, it is postulated that the dune sand was removed con- l jcomitantly as it was deposited across the mouth of the river either by (1) the ancestral river prior to uplift, (2) the antecedent river during uplift, or (3) by the streams that drained the southern slopes of the Baldwin Hills subsequent to the uplift and change in course of the ancestral Los Angeles River. Considering the thickness and breadth of the existing dunes, it is likely that dune sand was removed 64 prior to uplift inasmuch as the transporting capacity of the streams postulated in the two alternatives does not appear adequate. Gan configuration Field evidence indicates that the coastal dune belt was juplifted and tilted slightly to the southwest. Whether this (reflects the uplift that caused deposition of the "50-foot [gravels," or a subsequent uplift cannot be ascertained. i i However, the elevated terrace of the Ocean Park Plain north £>f the gap tends to favor the former premise. If the es- ( carpment of Ballona Gap is a fault scarp as postulated by I [Poland and others (1959), then the existing configuration ! I jof the gap has been modified to such an extent as to mask I i jits fluvial history. ] Peat Deposits | Peat accumulates in two distinct environments: inter distributary basins with local peat accumulations and coast al marshes in which blanket peats cover large areas (Coleman and Smith, 1964, p. 834) . The former develops in restricted basins between active distributaries. The sediments are jcharacterized by intercalations of silt, clay and organic 65 remains which are contributed to the basins during river flooding. According to Coleman and Smith, this type of peat deposit displays a high sulphide content, is usually black, and displays limited lateral distribution. Brown spongy peat I I i ! \ Brown spongy peat up to 4 feet thick occurs at an ele- I yation of 69 feet within the confines of Ballona Gap. It is i (separated from an overlying clayey peat horizon by a zone i [ (comprised of interbedded coarse sands, silts and clays which (ranges in thickness from 4 to 8 feet and is separated from | the underlying "50-foot gravel" by a variable thickness of | jinterbedded fine sands, clays, and silts. The brown spongy j I c [peat is of the blanket type. The deposit, as determined | j jfrom bore holes, displays a southeasterly dip across Ballona 1 Gap similar to the "50-foot gravel." j It appears that subsequent to the deposition of the gravels a change in stream regimen ensued which led to the deposition of fine-grained materials. In turn, deposition ceased and a static condition was attained which led to the formation of the blanket peat. The buried blanket peat represents a former marsh in which peat development was arrested by the influx of coarse-grained deposits. Burial, 66 therefore, is direct evidence of a positive change in eleva tion resulting from subsidence and/or an eustatic change in sea level. Black clayey peat Overlying the coarse-grained detritus are discontinuous Iseams, pockets, and layers of black clayey peat and black I jpeat up to 1 foot thick intercalated with greenish-gray i jclays, and green silts, and fine sands occurring in a hori- i jzon that diminishes in thickness in an upstream direction i jfrom 14 to 4 feet. The top of this horizon is fairly con- j teistent in elevation, ranging from 89 to 92 feet above i present sea level. The upper portion of the peaty horizon, j i |the black clayey peat, contains an appreciable amount of transported adobe, indicating that active erosion of the ; | residual adobe source(s) has been periodic since the forma- i tion of the residual soil. Ground water is associated with the black peat. Sul phate content of the water is high, ranging from 450 to 11,200 ppm; cloride content is from 78 to 3860 ppm; and bicarbonate from 356 to 1130 ppm. pH is alkaline with values ranging from 7.7 to 8.7. 67 Subsidence Compaction, the reduction in volume of the sediments i since deposition, is included in subsidence. The amount of compaction undergone by the peats is not known. In-place jdensities of both the interdistributary and blanket peats j jshow a wide variation between 50 and 78 lbs./cu.ft. Mois- !ture or water content varied from 40 to 80 per cent. ! Peat beds are not encountered below the "50-foot i i 'gravel." Hence, subsidence as indicated by the black clayey | peat horizons has been operative since the deposition of the j jgravels within Recent time. Subsidence and accompanying I luplift in the Baldwin Hills is occurring at the present. j The isobase map issued by the office of the Los Angeles County Engineer shows that movement up to 0.25 feet has joccurred in the interval of 1961-62. i j Gaspur Aquifer l Physical character Beneath the confines of Dominguez Gap extending to San Pedro Bay and the alluviated area southwesterly of Dominguez Hill, a water-bearing fluvial deposit consisting of sand anc gravel ranging from 40 to 80 feet in thickness, exists 68 approximately 75 to 85 feet below the ground surface. The deposit is comprised in its lower part of clean gravels to | icobble size and an overlying part, generally 20 to 50 feet thick, of medium to coarse sand. Discontinuous elongate I lenses and pockets of silts and clays occur within the upper part. The petrology of the cobbles indicates that they were mainly derived from the San Gabriel Mountains. I j The deposits are not exposed within the area of study jand are only known from well logs. However, the gravelly rphase is exposed in the Los Angeles Narrows in an area i bounded by the Los Angeles River and the Harbor Freeway. ! In Dominguez Gap, the channel containing the Gaspur I deposits is cut into fine-grained deposits of Upper Pleisto- | Icene age. Presumably, these deposits also underlie the i aquifer in San Pedro and well logs indicate that the aquifer i may even extend under San Pedro Bay. In the area of study, i the base of the aquifer has a gradient of about 10 feet per i jnile, from about 60 feet below sea level near Compton to 1170 feet below sea level at the coast. Contours (Plate V) i plotted on the base of the aquifer indicate that the depos its have not been disturbed by the folding responsible for the Gardena Syncline; however, they appear to be arched along the Newport-Inglewood Fault zone. 69 Origin I I The Gaspur was deposited in the Recent by an ancestral I I jsan Gabriel River; and undoubtedly some deposition was con tributed by the Los Angeles River subsequent to its change i in course caused by the Baldwin Hills uplift. It is pos- ! Isible that the upper fine-grained portion of the deposit ■reflects this deposition. However, no substantiating data i I are presented. ! Whether or not the Gaspur is the time equivalent of i |the "50-foot gravel" cannot be said with certainty. The i |lower gravelly part of the Gaspur could be older, as data ! indicate that it was deposited by the ancestral San Gabriel jRiver. j | Alluvium A distinction is made between transported adobe soil i and alluvium although in a strict sense the former is allu- I jvium. This was done in order to show the geologic and I j environmental history undergone by the adobe soils. Allu vium is here considered to be those deposits (1) of a transitory type occurring in ephemeral stream channels, and (2) older alluvium which predates that of both (1) and the 70 transported adobe soil. Two large areas of alluvium were mapped. The first underlies the central portion of the Torrance Plain extend ing westward to the Los Angeles River and the second is in jthe Walteria Lake area, the Torrance Fan. I i ! i Older alluvium i i | Sediments comprising the alluvium of the Torrance Plain las noted in borings and exposed in several pits from which j i clay deposits were mined for the manufacture of bricks and in the Gardena Drainage Sump consist of yellow (10 YR 6/4), 1 ifine-grained, dense sands, silts, and clays which apparently occupy a depression developed in Upper Pleistocene sedi- i ! ments. Water well logs indicate that the Upper Pleistocene ) sediments are warped to form the Gardena Syncline. I About 50 feet of these flat-lying sediments are exposed lin the artificial cuts within the pits. Approximately 90 i per cent of the exposed alluvium is finer than 0.42 mm and the sand size fraction consists predominantly of angular flakes of fresh biotite and angular, sharp grains of quartz. Biotite content varies between 15 and 30 per cent. Plagio- clase fragments are common. Some of the sand grains reflect their granitic provenance, being comprised of aggregates of 71 the above minerals. The source of the alluvium could either be the granodiorites exposed in the Hollywood Hills or the granitics of the San Gabriel Mountains. Considering the distance of transport from the latter source, the angularity jof the mineral grains and the freshness of the biotite I iflakes would preclude the San Gabriel Mountains as the jsource. Furthermore, the mineralogical composition of sands I jfrom the San Gabriel River, which has its headwaters in the I jsan Gabriel Mountains, is much different from that of the jalluvium. It is presumed that the alluvium was deposited by the 1 !Los Angeles River as this is the only through-flowing stream that drains, among other areas, the Hollywood Hills. f - ilf the alluvium is considered a flood plain deposit because j :of its fineness, then one is hard-pressed to account for the idepositional occurrence because of the restriction of topo graphy as the highs along the Newport-Inglewood Uplift separate the present course of the Los Angeles River from the limits of the alluvium as mapped, unless deposition was prior to uplift. A broad saddle separates the Dominguez Hill from the southern extremity of the Rosecrans Hills. Northeasterly of this saddle in the Compton area fluvial deposits which 72 are similar to the alluvium in the Gardena-Torrance area are within a few feet of the ground surface. Thus, it is con cluded that the alluvium was deposited by the Los Angeles River whose outlet was blocked as the result of continuing Recent uplift along the Newport-Inglewood Fault zone. Be cause the alluvium is flat-lying, deposition was probably linto an interior trough or basin created by the folding that ■formed the Gardena Syncline. In addition, it does not ap- j ipear that the basin subsided concomitantly with deposition | jinasmuch as the alluvium shows no indication of a basinward •dip. The broad saddle between Dominguez and Rosecrans Hills i iis a wind gap which undoubtedly has been modified by con tinuing uplift. i ! I i The alluvium is younger than the Gaspur Aquifer inas- i | Imuch as the alluvium overlies this fluvial deposit. Because | ithe "50-foot gravel" was not deposited by the Los Angeles i River but by streams draining both the Baldwin Hills and the southerly slopes of the Santa Monica Mountains, there is no way to determine the age relationship between the alluvium and the "gravels." The alluvium south of Dominguez Hill which occurs as a tongue-shaped wedge between the outcrop limits of the un named Upper Pleistocene deposits is unlike the alluvium just 73 described. As exposed in several excavations for cut and I jcover dumps, the alluvium is comprised of brownish-gray to !olive-gray clayey silts and clays. Thickness of the allu vium decreases from approximately 55 feet along Alameda Street to a feather edge in a northwestern direction within j jthe confines of the several stream channels that drain both !the older alluvial and Upper Pleistocene surface. The main t jstream that supplied these alluvial sediments prior to i t jintegration of the drainage by the Los Angeles County Flood jControl District was Laguna Dominguez. 1 iTorranee Fan j The Torrance Fan, which is along the toe of the low I j jfoothills of the Palos Verdes Hills, encompasses about 1900 | jacres and is approximately 2.75 miles wide in an east-west I jdirection and 1.2 miles long down the slope of the fan (Fig. | |4). It is comprised of an older portion occupying approxi mately the easterly quarter of the feature and a younger portion comprising the remainder which in turn consists of two coalescing fans having a common toe or apron. The apex of the older fan is George F Canyon, which in the Palos Verdes Hills has incised the Miocene and Pleisto cene sediments in the low foothills. _bordering the main LEGEND ALLUVIUM UNNAMED UPPER PLEISTOCENE SAN PEDRO FORMATION = 7 PACIFIC CO AST HIGHW AY ^ ” f ~ M TOPOGRAPHY FROM U S G EO LO G ICAL SURVEY t L6hG 8EACH SHEET, I95J AREAL DISTRIBUTION OF THE TORRANCE FAN 74 PLEISTOCENE DEPOSITS MATION PROFILE A PROFILE B PROFILE C PROFILE SCALE : HORIZONTAL: 2 0 0 0 ' VERTICAL • ZOO' FIGURE 4 75 hills. The main body of the older fan rests on reddish- jbrown, weathered silty sands of Palos Verdes age which dis- J Iplay a well-developed "A" horizon soil several feet thick. Fan-head and midfan areas are composed of a relatively thin* | jto 6 feet, poorly sorted mixture of adobe soil and platy j jshale fragments. This portion of the fan is more deeply weathered and displays a more gentle topography than the iyounger portion. i I The apices of the younger portion of the fan are both jAgua Magna and Agua Negra Canyons, which are incised into jthe San Pedro Sand and the unconformably overlying Palos iVerdes Sand. Slope angle along profiles A and B (Fig. 4) iare 3/4 to 3° and the slope profile is concave upward. The I [surface of the fan-bay (Davis, 1938, p. 1374), fan-head and I imidfan is composed of adobe soil intermingled with platy [fragments of shale up to 6 inches in length and discoid, jpebble to cobble size, particles of silicified limestone. I jwith increasing distance down the fan, the shale and lime- | stone fragments are smaller in size and are absent near and at the toe. Borings along the fan apron encounter adobe soil under lain by "A" and "B" horizon silty sand soils developed on sediments that are Upper Pleistocene in age. In its westerr. 76 portion, the fan laps onto older dune sand (Fig. 5). A we11-developed "A" and a thin "B" soil horizon have formed Ion the older dune sand surface. i | ' Alluvium in the western portion of the fan, which ap- i i ipears to be restricted to the areal extent of Walteria Lake, jis composed of dark gray (2.5 YR 4/1) sandy illite clays and sands. The mineralogy of the sand indicates its source ! is the San Pedro Sand and undoubtedly it was deposited as ia result of stream downcutting of Agua Negra Canyon. i Borings within the upper reaches of the midfan area I encounter poorly sorted sediments (SQ = 6.7), consisting of j iadobe and shale fragments (approximately 40 per cent) with 'interbeds to 3 feet thick of dark brown adobe soil not con taining shale fragments. This sequence is limited to 45 ifeet in depth below which the fan detritus consists of ^alternating layers of gravelly, granule to pebble size, jsandy silts and yellow to brown clays. Petrologically, the i I jgravels are similar to those in the San Pedro Formation. Those Upper Pleistocene sediments at the toe of the fan were not encountered to the total depth of exploration, 55 feet in the midfan area. It appears, then, considering the distance between borings (0.65 mile), that the younger portion of the fan was either deposited in a trough or in a 77 Fig. 5.— Walteria Lake Drainage Sump. Upper ! Pleistocene deposits are overlain by older dune sand. ! Note the soil horizon at the top of the dune sand, j above drainage bench. In turn the dune sand is overlain by alluvium of the Torrance Fan which at the surface ! displays a 3-foot thick blanket of transported adobe | soil. The older dune sand on the skyline in center of photograph is covered with residences. The youngest terrace of the Palos Verdes Hills on the skyline at the left of photograph. View looking west toward the west wall of the sump. i j j 78 subsiding area. If a trough did exist, it may have been jrelated to movement of the Palos Verdes Fault, inasmuch as i |the Upper Pleistocene Palos Verdes Sand is affected by the jfault. On the other hand, because of the weathered nature I jand relatively thin deposits of the older portion of the |fan, this portion appears to have been uplifted. Further more, the younger fan laps onto it. The seemingly anomalous i jsituation could then be related to the uplift and folding ithat created the Gaffey Anticline and Syncline. Because I [the Upper Pleistocene sediments exposed at the crest of |Gaffey Anticline are affected, the uplift must be post- | iupper Pleistocene and therefore occurred during Recent time I According to Woodring and others (1946, p. 110), post-Palos 1 I Verdes deformation is probably represented by slight de- i j [formation of alluvium along the crest of the Gaffey Anti- i |cline and the anticline may still be growing. ; The topography of the western portion of the younger j jfan indicates that subsidence has occurred since deposition. Because the fan deposits are interpreted as the result of mud-flow and sheet flood deposition, the mechanics of such deposition would allow the deposits to flood any low area as in the northwesterly part of the fan. Immediately adja cent to and westerly of the fan a pronounced depression 79 exists. If this depression were in existence at the time of fan deposition, then it would have been filled with detri tus. Inasmuch as it has not, the depression must be related to subsidence. Profiles A and C in Figure 4 are drawn with the vertical scale exaggerated to show this phenomenon. [Whether the subsiding area is a local isolated feature due ! [to compaction of the fan detritus or related to a major [structural trend could not be ascertained. Nonetheless, I jthe area of subsidence coincides with the axis of the Lomita 1 jSyncline. For reasons stated above, the Torrance Fan, at least I * Ithe upper 45 feet of sediments of the younger portion of I the fan which contain transported adobe soil, is younger \ | than the older alluvium of the central portion of the Tor- j ranee Plain. Furthermore, these sediments containing the [reworked adobe soil represent deposition that occurred since the formation of the residual adobe soil on the Palos Verdes t t ! ! Hills. Inasmuch as the adobe overlying the residual soil jdeveloped on the alluvium of the Gardena-Torrance area is a transported deposit, as will be demonstrated further in the text, the residual soils are therefore older than the upper 45 feet of fan sediment. There is no way to date the lower sequence of the fan 80 sediments. Intuitively, it is believed that they are young er than the older alluvium and may be the time equivalent of the younger alluvium. Beach Deposits I I 1 i | Recent beach deposits consisting of sand and gravel Jform a continuous narrow strip fringing Santa Monica Bay. j jThey are the chief source of material which is supplied to ithe coastal active dune belt. The beach sands consist for | jthe most part of individual mineral grains. Heavy mineral janalyses show a high concentration of augite at the upper jlimits of Santa Monica Bay near the city of Santa Monica, jgiving way to hornblende further south along the coast near i ! jPoint Fermin. The black sands of Redondo and Hermosa i | [Beaches have been mined in the past because of the high [percentage of contained ilmenite and magnetite (Stimson, i 1957) . Beaches consisting predominantly of gravel occur at the base of many of the cliffed shores of the Palos Verdes Hills. They commonly occur on the sides of projecting headlands rather than at the ends, and the beaches are usu ally less than 100 feet in width. Most of the boulders, cobbles, and pebbles are subrounded to rounded and consist 81 of igneous and metamorphic rock. Locally, clasts of lime stone, schist, and cherty shales which are representative of the bedrock types of the Palos Verdes Hills are common. | Individual gravel beaches usually display a longshore jdecrease of grain size and a decrease of sorting coefficient i iaway from the source of the gravels (Emery, 1960, p. 184). IA preferred orientation of individual clasts is usually well I jexhibited with the short or C-axis dipping landward. Well i jdeveloped gravel beaches occur at Abalone Cove, Vicente Cove and Bluff Cove. j Soils I Soils of the southwestern portion of Los Angeles County i S jare for the most part comprised of dark gray (10 YR 3/1) to black (10 YR 2/1) clays which are termed "adobe" by agrono mists and soil engineers. By definition, adobe is an allu- ! ! ivial or playa clay which occurs in arid regions. Inasmuch as common usage has ingrained the term in the literature, the term "adobe" will be used by the writer for those black clayey soils which occur in the area of study even though the climate is semi-arid. The origin of this soil poses a problem in that dis tribution is sporadic although large areas are covered. 82 Moreover, the sediments underlying these adobe clays are varied in composition, indicating to the casual observer I Ithat the adobe was derived from different underlying sedi- i |ments . ] | | Other types of soil occur in the study area besides !the adobe clays. Their distribution and origin is discussed i 'as they relate to the Recent geologic history of. the region. Sedimentary analyses i j In order to determine the origin of the adobe soils, jsurface samples as well as those from auger borings were mechanically and statistically analyzed in the laboratory. I |A total of 400 samples were treated. The analyses present- ! |ed, coupled with field observation and mapping, form the basis for the interpretation of whether the soils are resid- j lual or transported. i Methods ! i X-ray diffraction.— Samples of the adobe soils as well as from the underlying rocks and sediments were prepared by gentle crushing and then dispersed in distilled water to l settle for 123 minutes to obtain clay size particles; a procedure outlined by Krumbein and Pettijohn (1938, p. 166). 83 U-shaped stainless steel supports containing 3 glass slides were lowered into crocks containing the dispersed material to a depth of 10 cm and left for 12 hours. Clay size par ticles, according to Bradley and others (1937, p. 216), settle with the (001) faces parallel to the surfaces of the islides. The air-dried oriented slides were then examined j jwith a Norelco recording scintillation counter diffracto- f jmeter with nickel filter and copper radiation at 40 kv and !20 ma. The instrument settings were as follows: Chart j jspeed, 1/2° per minute; scale factor, 4; slit, 1°. One of I ;the 3 slides was untreated and one was treated with ethylene; j iglycol (MacErvin, 1951, p. 115). The third slide was placed f jin a muffle furnace and heated to 550° C. I Montmorillonite as used here is a group term for clay ] jminerals which display diffraction peaks between 10 and |14A, which collapse to loA upon heating to 550° C, and swell to 1?A upon saturation with ethylene glycol. No attempt i jwas made to distinguish between individual minerals in the montmorillonite group as their identification by X-ray diffraction is almost impossible in complex mixtures. o Micaceous minerals having an 001 peak at 7A which dis appears upon heating at 550° C are termed kaolinite. Unless! the clay is monomineralic, it is not possible to differen- 84 tiate kaolinite from other members of this group and there fore, kaolinite refers to the group designation. Grim, Bray, and Bradley (1937) proposed the term illite jfor all platy minerals that possess a strong reflection at i |10A which remains unchanged following heat treatment and i I jglycolation. i i | ! ! Coarse fraction analyses.— Staining techniques as devel- ) loped by Hayes and Klugman (1959, p. 228) were employed to | ^determine the percentages of calcite and quartz as well as i the type of feldspar present in the sand fraction of the i adobe soils from the Torrance Plain. i j j Hydrometer analyses were utilized to determine the [ percentage of total sand occurring in the adobe soils of j the Torrance Plain. Furthermore, the sand fraction thus iobtained was studied under the microscope to determine the 1 i percentage of frosted sand grains. Rock fragments in the isand fraction were also identified utilizing a binocular microscope. Grain size.— One of the fundamental principles on which mechanical analysis is based is that particles settle with a constant velocity in a fluid medium. The frequency dis tribution is simply the arrangement of the numerical data 85 according to size. Under certain conditions of deposition sedimentary particles may assume a given size distribution depending on the depositional agent. Hence, cumulative Jcurves, based on pipette and sieve analyses were utilized to j (determine grain size frequency of the adobe soils as well as the other soil types in the area of study. i j Consistency limits.— Increasing the water content of a i 'clayey soil changes its consistency and the soil passes from j i a solid state through a plastic state and finally to a i i iliquid state. Most soils possess a characteristic set of \ jlimits to these 3 states. These limits of consistency were i [established according to arbitrary criteria in empirical I I [tests proposed by Atterberg (Terzaghi and Peck, 1948, p. i ' (32—36). The liquid limit of a soil is the water content, [expressed as a percentage of the weight of the oven-dried | [soil, at the boundary between the liquid and plastic states, i jwhereas the plastic limit measures the boundary between the i plastic and semi-solid states. The plasticity index is the numerical difference between the plastic and liquid limits and thus defines the range of moisture content in which the soil is plastic. The consistency limits were determined for that frac- 86 tion of the adobe soils smaller than 0.42mm in accordance with the procedures outlined by Atterberg. i i | Carbon analysis.— Carbon analysis, utilizing a Leco Car bon Analyzer, was performed to determine the amounts of total carbon in the adobe soils. Alkalinity.— The symbol pH designates the negative loga- i jrithm to the base 10 of the hydrogen ion concentration in ! ' i imoles per liter, being 0 to 7 for acids and 7 to 14 for | bases. pH of the adobe soil (slurried with fresh distilled i jwater) was measured by a Beckman pH meter utilizing calomel land glass electrodes. i | Sulphate content.— The percentage of water soluble sul- ! jphate was computed from an extract of the adobe soil- |distilled water solution according to a procedure outlined | in the Earth Manual of the Bureau of Reclamation (1960). Results and conclusions X-rav diffraction.— The major portion of the Palos Verdes Hills is covered by adobe soils which are generally a few feet in thickness. Samples for X-ray study were obtained from both the soils and the underlying rock types (sample 87 nos. 101-107, 117, and 140). The samples of the rock were obtained below the soil-rock interface to assure that the rocks were not contaminated by the overlying soils. The diagnostic clay mineral in this series of samples is mont- | imorillonite with non-clay minerals consisting of quartz and I I jfeldspars. The rock types representative of the 3 members !of the Miocene Monterey Formation contain only the clay jmineral montmorillonite. The overlying adobe soil also contains this clay mineral (Table 5). Because of this re- I jlationship, it is concluded that the soils are residual, i [having been derived from the weathering of the underlying I jrock. i ! Along the west side of Crenshaw Boulevard approximately 1 ! '0.5 mile north of the intersection of Crest Road, the soils I ’ jare in fault contact with the Altamira Shale (Fig. 6). i ! Approximately 10 feet of soil is preserved along this fault, [indicating that the soils at least in places were much | jthicker than now exist. X-ray traces depicted in Figure 7 are for soils obtained from the surface and at intervals of 3 feet along the fault. The clay mineral in this series of samples is also montmorilIonite. The most abundant clay mineral in the glauconitic siltstones of the Repetto Formation of Pliocene age is TABLE 5 X-RAY DIFFRACTION DATA— PALOS VERDES HILLS Sample Number Sediment Type Formation Age Predominant Clay Mineral Other Clay Mineral Non-Clay Minerals 101 Adobe Soil Recent M .. Q, F 101-1 Limestone Altamira Miocene — — C 102 Adobe Soil Recent M : — Q, F 103 Adobe Soil Recent M — Q, F 103-1 Diatomite Valmonte Miocene M — — 104 Adobe Soil Recent M — G 104-1 Basalt Altamira Miocene M — — 105 Adobe Soil Recent M — — 105-1 Shale Altamira Miocene M — — 107 Adobe Soil Recent M — Q, F 107-1 Mudstone Malaga Miocene M — — 117 Adobe Soil Recent M — Q, F 117-1 Mudstone Malaga Miocene M — — 140 Siltstone Repetto Pliocene M I Q, F M Montmor i1lonite F Feldspar I Illite G Gypsum Q Quartz C Calcite 00 00 89 i j Fig. 6.— Adobe soil in -fault contact with the Altamira Shale. View looking east from Crenshaw Boule- ; vard. Upthrown side of normal fault on the viewer's I right. Note drag folding of the shales. Crush zone i is about 6 feet wide, consisting of broken pieces of ! shale mixed with soil. PLAGIOCLASE | QUARTZ MONTMORILLONITE MONTMORILLONITE MONTMORILLONITE MONTMORILLONITE I 06-2 MONTMORILLONITE 106-3 X -R A Y DIFFRACTOMETER TRACES OF ADOBE SOILS USING NICKEL FILTERED COPPER RADIATION FIGURE 7 91 montmorillonite (sample 140); illite is the subordinate clay mineral. Non-clay minerals are quartz and plagioclase. The illite occurrence probably represents original accumulation |of the mineral. However, as noted by Hendricks and Ross I (1941), glauconite is a dioctahedral illite with consider- i 3+ 3+ i lable replacement of Al by Fe and thus illite may have formed through marine diagenesis of the glauconite. Fur- i jthermore, Barshad (1950) has shown in the laboratory that at. jordinary temperatures and pressures a material substantially ilike illite is produced from montmorillonite when all the .exchange positions are occupied by potassium ions and the ^material is thoroughly dried at about 110° C. I The predominant clay mineral in the adobe soil and i I underlying Upper Pleistocene (Palos Verdes) sediments of (the Baldwin Hills is montmorillonite (sample nos. 126, 127, j ;128) (Table 6). Some illite is present, although not in iall samples. Because both the soils and the underlying isediments display similar clay mineralogy, it is concluded that these soils are residual. Talc in sample 126 from the adobe soil marks the only occurrence of this mineral. It is believed that the talc formed from hydrous alteration in the zone of weathering from either amphiboles or pyroxenes. Grains of augite and hornblende are common in the underlying TABLE 6 X-RAY DIFFRACTION DATA— DOMINGUEZ AND BALDWIN HILLS Sample Number Sediment Type Formation Age Predominant Clay Mineral Other Clay Minerals Non-Clay Minerals Baldwin Hills 126 Adobe Soil Recent M — F, T 126-1 Adobe Soil Recent M — Q, F 126-2 Sand Palos Verdes U. Pleist. M — — 126-3 Sand Palos Verdes U. Pleist. M — F 127 Adobe Soil Recent I M Q, F 127-1 ■Sand Palos Verdes U. Pleist. M — Q, F 127-2 Silt Palos Verdes U. Pleist. M — Q, F 128 Adobe Soil Recent M I Q, F 128-1 Adobe Soil Recent M I Q, F 130 Adobe Soil Recent M I 3 K Q, F Dominguez Hill 125 Adobe Soil Recent M & I (interlayered) 125-1 Adobe Soil Recent M — Q, F 125-2 Silt Palos Verdes U. Pleist. M — C M Montmorillonite I Illite K Kaolinite Q Quartz. C Calcite F Feldspar T Talc IX) ro 93 Upper Pleistocene sandy sediments. j j The adobe soil (sample 125) capping Dominguez Hill I I 1 icontains both montmorillonite and illite clay. However, \ ithe X-ray trace displayed a peak at 12.28A and upon satura- i |tion with ethylene glycol did not swell comparable to mont- i imorillonite. Because clays may be composed of more than one clay mineral in a mixed arrangement, either randomly or iregularly interstratified, the peak as recorded by the trace |is interpreted as a mixed-layer mineral comprised of the |two. Mixed layers of illite and montmorillonite as well as chlorite and verraiculite are common (Grim, 1953). The two clay minerals also occur in the "B" horizon soil. Further more, the X-ray trace of the limey siltstone underlying the i soils displays a montmorillonite peak (Table 6). Thus, it is concluded that these adobe soils are residual. I i The only clay mineral in the adobe soils and the under lying Upper Pleistocene sediments in the Rosecrans Hills is jmontmorillonite (sample 114 and 115). Based on the X-ray I traces, it is apparent that the adobe soil is also residual (Table 7). X-ray traces indicate that the adobe soil of the Tor rance Plain is predominantly comprised of montmorillonite (Table 8). Figure 8 depicts X-ray traces of adobe soil TABLE 7 X-RAY DIFFRACTION DATA— ROSECRANS HILLS Sample Number Sediment Type Formation Age Predominant Clay Mineral Other Clay Minerals Non-Clay Minerals 114 Adobe Soil Recent M — Q, F 114-1 Adobe Soil Recent M — Q, F 115 Adobe Soil Recent M — Q, F 115-1 Sandy Clay Palos Verdes U. Pleist. M — Q, F 115-2 Sandy Clay Palos Verdes U. Pleist. M — — 129 Adobe Soil Recent M I Q M Montmorillonite I Illite Q Quartz F Feldspar kd TABLE 8 X-RAY DIFFRACTION DATA— TORRANCE PLAIN Sample Sediment _ , Predominant Other Clay Non-Clay L m Formation Age . w. , J , Number Type Clay Mineral Minerals Minerals 111 Adobe Soil Recent M — Q, P 112 Adobe Soil Recent M — Q, P 113 Adobe Soil Recent M — Q, F 116 Adobe Soil Recent M — Q, P 118 Adobe Soil Recent M — Q, P 118-1 Sandy Clay Alluvium Recent M I Q, F 118-2 Sandy Clay Alluvium Recent M — Q, F, 118-3 Clay Alluvium Recent M I Q 118-4 Clayey Sand Alluvium Recent M I Q, P 119 Adobe Soil Recent M — Q, f, 119-1 Sandy Clay Alluvium Recent M K Q, P 119-2 Sandy Clay Alluvium Recent M I Q, F 131 Adobe Soil Recent M — Q, F 132 Adobe Soil Recent M — F 133 Adobe Soil Recent M — Q, F 134 Adobe Soil Recent M I, K Q, F 135 Adobe Soil Recent M Q, F U1 TABLE 8— Continued Sample Number Sediment Type Formation Age Predominant Clay Mineral Other Clay Minerals Non-Clay Minerals 136 Adobe Soil Recent M Q, F 138 Clay Loam Soil Recent I — Q, F 139 Adobe Soil Recent M — Q, F 141 Clay Alluvium Recent I M Q, F 141-1 Silt Alluvium Recent I M Q, c 141-2 Clayey Silt Alluvium Recent I M, K Q, F M Montmorillonite F Feldspar I Illite A Actinolite (?) K Kaolinite C Calcite Q Quartz vO MONTMORILLONITE Sample No. 120 FELDSPAR ILLITE CHLORITE MONTMORILLONITE 121 FELDSPAR CHLORITE FELDSPAR CHLORITE MONTMORILLONITE 122 FELDSPAR CHLORITE X-RAY DIFFRACTOMETER TRACES OF ADOBE SOILS USING NICKEL FILTERED COPPER RADIATION FIGURE 8 samples at 1 foot in depth. The important aspect of these I jsamples is the presence of chlorite. Weiss and Rowland i I 1(1956) demonstrated that chloritic clay minerals dehydrate I at variable temperatures beginning at 550-650° C. Intensi- ■ * ;fication of the 14A peak accompanies dehydration. Thus, if o la peak at about 14A was observed after heating to 550-650° ■ ' ! C for 1 hour, it was attributed to chlorite. j Diagenetic formation of clay-size chlorite in some j . | ‘ Recent marine sediments was proposed by Powers (1954). The- ; i i proposed mechanism for chlorite formation is the lateral growth of brucite between the basal surfaces of montmoril- : j I Ionite and of micas stripped by weathering of part of their potassium. Conditions are considered far more favorable in sea water for the growth of chlorite than in fresh water bodies. Inasmuch as the chlorite in the soil samples could not have been formed in either environment, it is believed that the chlorite is not due to diagenetic formation but rather represents transport of the mineral from the parent i [source. In this instance, the Franciscan (?) chlorite schists exposed in the Palos Verdes Hills are presumably the source rocks. On the basis of thousands of X-ray anal yses of clay minerals from different sediments, Weaver 1(1958) concluded that clay minerals are only slightly 99 modified by their depositional environment and reflect pri marily the character of the parent material. ; Chlorite was not found in the adobe soil in the north- i ierly portion of the Torrance Plain; the predominant clay i jmineral is montmorillonite. Just north of the constriction |of the adobe ground-surface near Hawthorne, X-ray traces of ; i sample 134 indicate that montmorillonite, illite and kao- j j j |linite are present in about equal amounts in the adobe soilj i | The same clay mineral association occurs in the adobe soil ! ■within Ballona Gap (sample 130). The writer is at a loss to explain the presence of kaolinite as the X-ray traces do : i ■not indicate the presence of this mineral in the adobe or jUpper Pleistocene sediments of the Baldwin Hills; and pre- [ i Isumably from field evidence the adobe in the northerly por tion of the Torrance Plain as well as Ballona Gap was de- j rived from this source. Although kaolinite can be trans formed from montmorillonite in the laboratory, the process as outlined by Caillere and Henin (Grim, 1953), because of I its attendant chemical treatment, would not occur in nature. j j Possibly X-ray studies of the clays in the Lower Pleistocene and Pliocene sediments of the Baldwin Hills may render an i l explanation. | In the Walteria Lake area at the extreme southwesterly 100 part of the Torrance Plain, a portion of the alluvium com- iprising the Torrance Fan which consists of dark gray, clayey i I Isands, contains appreciable amounts of illite (sample series 1109) (Table 9). It is possible that montmorillonite in the alluvium is the result of downward migration of the colloid al clay particles from the overlying adobe soil. In the i i presence of calcium carbonate and bicarbonate, montmoril- i- ■Ionite clay can exist in a flocculated form. As bicarbonate is leached downward, the electrolyte concentration of the ; j adobe soil is reduced below the flocculation value of the clay. Abetted by the protective action of the colloidal i soil humus, the clay disperses. Hence, the fine clay par- .ticles are carried by the percolating waters to the allu- i yium. On the other hand, the sand mineralogy of the allu vium indicates its source to be the San Pedro Formation. The clays within these Pleistocene deposits contain illite and therefore, the montmorillonite-illite association may be the result of deposition. The adobe soil on the surface of the Torrance Fan is i j predominantly comprised of montmorillonite. However, illite and chlorite also occur and presumably these clay minerals i lare of depositional origin and not due to diagenesis of the i I i jmontmorillonite; the source is doubtless from the Repetto TABLE 9 X-RAY DIFFRACTION DATA— TORRANCE FAN Sample Number Sediment Type Formation Age Predominant Clay Mineral Other Clay Minerals Non-Clay Minerals 108 Adobe Soil Recent M — Q, F 109 Clayey Sand Alluvium Recent M I — 109-1 Clayey Sand Alluvium Recent M I Q 109-2 Clayey Sand Alluvium Recent M ■ I Q 109-3 Clayey Sand Alluvium Recent M I Q, F 109-4 Clayey Sand Alluvium Recent M I — 110 Adobe Soil Recent M — Q, F 110-1 Sand Palos Verdes U. Pleist M I Q, F 110-2 Sand Palos Verdes U. Pleist M K Q, F M Montmorillonite I Illite K Kaolinite Q Quartz F Feldspar 101 102 siltstone and the Franciscan schist. The clays in the underlying Upper Pleistocene sediments at the toe of the fan (sample series 110) contain both illite and kaolinite. i The alluvium immediately underlying the adobe in the icentral part of the Torrance Plain is a yellow (10 YR 6/4) I (calcareous clay loam; the lime is either distributed uni- j i j ■ formly or may be concentrated in spots, resulting in a mottled appearance. Although X-ray traces show that mont morillonite is the predominant clay mineral in these sedi- j ! I ; | jments, illite and kaolinite are present (sample series 118 and 119). It should be noted that illite and kaolinite occur neither in the overlying adobe nor in the adobe of ! the Palos Verdes Hills. Other X-ray traces of the alluvium (sample 141) reveal the predominant clay mineral to be illite with subordinate amounts of montmorillonite and kaolinite. The residual clay loam soil (sample 138) devel oped on the alluvial surface is comprised of illite. Adobe which overlies this residual soil contains only montmoril- l I ! Ionite. j Thus, the difference in clay mineralogy as shown by j I the X-ray diffractometer studies show that the adobe of the t i . i !Torrance Plain did not form from the weathering of the ! (underlying alluvium or the Upper Pleistocene sediments. It 103 is concluded that these adobe soils were derived from the jerosion of the residual adobes of the Palos Verdes Hills. i i | Coarse fraction analyses.— Stain test analyses of the ! * * isand fraction of the adobe soil of the Torrance Plain which i jare shown in Table 10 indicate that soda-lime feldspars are j the main mineral constituent along with quartz. In all | I s probability the soda-lime feldspars were derived from the erosion of the diabase or basalt exposed in the Palos Verdes Hills, as this is the closest source of these minerals. The calcite grains were derived from the limestones within the Altamira Shale. | : i i i i I Percentage of total sand, as determined from hydrometer 'studies, and the percentage of frosted sand is shown in Figure 9. It is noted that the percentage of total sand increases from the Palos Verdes Hills northward to the Haw thorne area. A portion of the sand is undoubtedly of eolian prigin as shown in the lower graph and was introduced during the time that the adobe clay was being deposited within the | porrance Plain. Moreover, the increase in percentage of j [frosted grains in the Torrance area is attributed to the jproximity of dune sand from the El Segundo Sand Hills I frosted grains were not found in the soils covering the 104 I i i ■ TABLE 10 j | STAIN TEST RESULTS, | PERCENTAGE OF NUMBER OF GRAINS Locality Sample Number Calcite Quartz Potash Feldspar Soda-Lime Feldspar Walteria 108 6 42 2 50 ! 110 5 46 3 56 Torrance 111 5 38 3 51 112 7 46 8 50 113 5 51 9 47 118 6 54 5 42 Lawndale 116 1 55 2 32 Hawthorne 121 48 7 D /o FROSTED SAND O F TOTAL SAND % TOTAL SAND 105 PALOS' VERDES W ALTE R IA HILLS TORRANCE LAWNDALE HAWTHORNE 60 40 20 DISTANCE 60 20 D IS T A N C E COURSE FRACTION ANALYSIS FIGURE 9 106 Palos Verdes Hills. | Rock fragments in the coarse fraction of the adobe soils of the Torrance Plain were identified under the micro scope . Fragments of glaucophane schist were conspicuous in I ithe adobe soil samples as far north as 174th Street; about | 8 miles from the closest source area. Occasionally, frag- ; ! i ments of porcellaneous and cherty shale were noted. Some | : j of the samples from an xsolated adobe remnant occupying a j i ilocal topographic high (elevation 55 feet) near the inter- ! section of the Harbor Freeway and Sepulveda Boulevard con tain along with the shale fragments pieces of unweathered | biotite. Mineral analyses of the Upper Pleistocene sands ■ I immediately underlying the adobe soil failed to disclose any of these rock types or minerals. It is inferred that these rock fragments were derived from rock types exposed !in the Palos Verdes Hills. The source of the biotite is believed to be the saussuritized basic igneous rock asso- i i iciated with the Franciscan (?) schists. ! The adobe within Ballona Gap occasionally contains granules and pebbles which are of the same petrologic com position as those Pleistocene gravelly beds underlying the residual adobe of the Baldwin Hills. Likewise, the adobe northwesterly of the hills contains granules of the same 107 petrologic composition. Sediments immediately underlying i jthese adobes do not contain gravels so that they could not jhave become incorporated if these were residual soils. i Grain size.— According to Trask (1932), a sorting coef- ificient (SQ) of less than 2.5 indicates a well sorted sedi- iment, a value of about 3.0 a normally sorted sediment, and a value greater than 4.5 a poorly sorted sediment. Because residual soils are the complex end-product of j ! ! :in-place weathering as influenced by such factors as cli mate, topography, drainage, time, and parent material, and jalthough in a strict sense they are sediments, the grain isize distribution can vary within the soil horizon at any i igiven depth or interval of time. It is apparent that be cause of weathering processes there would be a change in the particle size as the soil becomes zonal from a "C" to an "A" horizon. Regardless, cumulative curves were drawn, based on ipipette analyses, for those adobe soils which are considered jto be residual (Fig. 10) and the quartile measures computed (Table 11) so that a comparison could be made of the same iparameters for adobe soils that are considered to be trans- | ported (Figs. 11 and 12 and Table 12). Median diameter of CUMULATIVE CURVES RESIDUAL ADOBE SOIL 100 PALOS VERDES HILLS ROSECRANS HILLS BALDWIN HILLS DOMINGUEZ HILL 80 60 - i 40 20 MILLIM ETERS SIZE .001 FIGURE 10 j I 109 J TABLE 11 COMPARISON OP QUARTILE MEASURES OF RESIDUAL ADOBE SOIL 1 [ i \ Locality Md (mm) Q1 (mm) Q3 (mm) QDa So Sk 1 Palos Verdes Hills .0016 .0011 .015 .0069 2 .77 0.673 Dominguez Hill .030 .0012 „ 104 .0514 2 .94 1.386 Baldwin Hills .038 .004 .086 .0410 1.46 0.238 ' Rosecrans Hills .009 .0013 .074 .0363 7 .55 1.187 i i i CUMULATIVE CURVES TRANSPORTED ADOBE SOIL — HARBOR CITY — WILMINGTON — COMPTON — BALLONA GAP CUMULATIVE CURVES TRANSPORTED ADOBE SOIL HARBOR CITY WILMINGTON COMPTON BALLONA GAP 100 80 ~ D 40 20 MILLIMETERS SIZE 0 o . 0 0 1 FIGURE II CUMULATIVE CURVES TRANSPORTED ADOBE SOIL 100 TORRANCE FAN TORRANCE PLAIN (HAW THORNE) TORRANCE PLAIN ( LAW NDALE) TORRANCE PLAIN (TORRANCE) 80 60 m z - 40 m 20 MILLIMETERS SIZE .001 .0 1 O .l 1.0 FIGURE 12 TABLE 12 COMPARISON OF QUARTILE MEASURES OF TRANSPORTED ADOBE SOIL Locality Md (mm) Q1 (mm) Q3 (mm) QDa Sk | j i 1 Torrance Plain (Hawthorne) .0125 .0012 .100 .0493 3 .56 i 3 ! 0.814 I Torrance Plain (Hawthorne) .004 .0012 .032 .0159 1.94 1 2.150 Torrance Plain (Lawndale) .011 .0014 .017 .0078 2 .87 0.214 Torrance Fan .0014 .0011 .013 .0059 2.91 6.801 ; Harbor City .027 .0014 .300 . 1493 2.16 0.576 I BaIlona Gap .0108 .0014 .056 .0273 5.00 0.067 I Compton .0095 .0014 .060 .0293 4.83 0.930 Wilmington .015 .0014 .170 .0843 9.07 I 1.058 | 113 the residual adobe ranges from .0016 to ,038mm, whereas the itransported adobe shows a range from .1004 to .027mm, indi- I Seating that median diameters are not significant in differ- i jentiating between a residual or transported adobe. Further more, the similarity of the grade size of the 7 5 per cent j quartile does not permit differentiation of the two soils I i on this basis. Sorting coefficients show that both soil j I Jgroups range from poorly to well sorted; there being no ! ; i j 'suggestion from the arithmetical data that the transported j j adobe is better sorted than the residual adobe. Moreover, the quartile skewness is of no value in differentiating the i two soils as either group may show a positive or negative J departure. Therefore, based on this study, quartile meas- I ures apparently cannot be used to distinguish adequately between a residual and transported adobe soil. However, if a larger number of samples were analyzed, statistical anal yses may render more definitive results. Cumulative curves for the illite-bearing residual clay ]loam developed on the alluvium in the Gardena-Torrance area I I iare shown in Figure 13. There is a marked difference in j sthe grain size distribution of these clays compared to the I i I overlying adobe soil. i [ CUMULATIVE CURVES RESIDUAL CLAY LOAM UNDERLYING ADOBE TORRANCE PLAIN 100 80 m o m . 60 m 40 20 M ILLIMETERS SIZE .001 .01 0.1 FIGURE 13 114 115 Consistency limits.— Statistical studies of the Atterberg i jlimits of clays by Casagrande (1947, p. 803) have shown that jwhen the plasticity indices and liquid limits for a large inumber of clay samples from the same bed or from geological- I ily related deposits are plotted on a graph, the data approx- ;imate a straight line. Furthermore, the linear plots of ] i J clays of different geologic origin or environment occupy j ^different areas on the graph. j ; The relationship of liquid limit to plasticity index j ; j 'shown in Figure 14 for the adobe of the Palos Verdes Hills j ■ I and that of the Torrance Plain reveals that two environments are represented by the plots. The same distinction would hold whether or not the Torrance Plain adobe was residual. Thus, this evidence is only of a contributory nature and cannot in itself be utilized to distinguish between a transported or residual soil. Carbon content.— The adobe soils in the area of study jappear to have a high percentage of organic matter as at- ! tested by their dark color. Carbon analysis (Table 13) shows that a wide variation in total carbon is apparent and that carbon content cannot be used as a distinguishing criterion. It is interesting to note that the adobe 60 50 o PALOS VERDES ADOBE • TORRANCE PLAIN ADOBE 7 l i q u i d LIMIT LIQUID LIMIT - PLASTICITY INDEX H1 I-1 Jcn FIGURE 14 PLASTICITY INDEX TABLE 13 CARBON ANALYSIS Sample Number Locality Per Cent Total C Per Cent C After HCl Leaching Difference Per Cent CO3 Residual Adobe 101 Palos Verdes Hills 1.26 .99 .27 106 Palos Verdes Hills .27 .15 .12 106-1 Palos Verdes Hills .00 .00 .00 106-2 Palos Verdes Hills .00 .00 .00 115 Rosecrans Hills .77 .54 .23 125 Dominguez Hill .82 .25 .57 128 Baldwin Hills 2.49 1.72 .77 Transported Adobe 108 Torrance Plain .84 .78 .06 110-1 Torrance Plain .40 .30 .10 116 Torrance Plain .82 .77 .05 118 Torrance Plain .54 .53 .01 118 preserved along a fault, samples 106-1 and 106-2, contains j ho carbon. 1 i i i | Alkalinity.— Alkaline soils occur predominantly in arid i regions. They differ, in one respect, from acid soils in ! i the direction of ground water movement; upward in alkaline I 'soils, downward in acid soils. The upward movement is f accompanied by precipitation of salts, mainly calcium and sodium, in the soil profile. The attendant high pH of j | | I alkaline soils is attributed to these salts. According to Beeking and others (1960, p. 252), soils may be divided into 3 categories dependent upon their water | retention characteristics; mainly, wet soils whose pH ranges jfrom 3.7 to 8.5 (?), waterlogged soils with a pH range of , |5.0 to 8.0, and normal soils that display a pH range of 2.8 to 10.0 plus. Wet soils are subject to seasonal waterlog- i ging and may be dry during other periods of the year. The adobe clays of this study, because of the Mediterranean type i pf climate, are classified as wet soils. The correlation of i i high pH and semi-arid conditions of formation suggests that under waterlogged conditions, soils of high pH would not i form. Acidity in soils may arise from several different 119 sources. Leaching, weathering, plant intake, the amount of humus and its composition, and influence of soluble salts, i jamong other things, influence the acidity of a soil. In ! j jalkaline soils, the pH is principally influenced by ex- ichangeable calcium or by exchangeable sodium, j The alkalinity of the adobe appears to increase in the direction of transport northward from the Palos Verdes Hills to the Hawthorne area (Table 14). Furthermore, the residual 1 1 , [ iadobe capping the Palos Verdes and Rosecrans Hills is more I jacidic than the adobe of the Torrance Plain. Also, within the Torrance Plain, the adobe soils are less alkaline with depth and there is a pronounced increase in alkalinity for J ithose alluvial clays underlying the adobe. From clay synthesis experiments by Grim (1953), acid conditions apparently favor the formation of the kaolinite I 1 type of clay, whereas montmorillonite would form under j alkaline conditions. i Sulphate content.— Inasmuch as the adobe clays of the j Torrance Plain were presumably deposited in a low-lying larea, it was thought that deposition may have taken place junder a paludal environment. Therefore, percentage of water i ! soluble sulphates was determined for both these soils as TABLE 14 120 pH AND SULPHATE CONTENT OF ADOBE SOILS i I ! Locality i ) Sample Number Water Soluble Sulphate (Per Cent) pH Palos Verdes Hills 101 .028 7.2 | 102 .062 6.2 i 103 .056 6 .6 1 104 .062 6.0 1 105 .075 6.4 Torrance Plain i Torrance 111 .003 6.0 j .004 6.0 118 .007 7.0 .004 7.0 .003 6.8 [ .004 6.5 1 .007 7.0* Lawndale 113 .009 7 .6 . .007 7.6 .005 7.3 .006 6.9 .006 7.5* Hawthorne 116 .004 8.1 .001 7.2 .008 8.8 .005 7.0 ■ .008 7.9* j Rosecrans Hills 115 .040 6.0 .037 6.5 129 .030 6.0 .078 6 .4 *Determinations for the underlying alluvial clays. 121 jwell as the adobe soils capping the Palos Verdes and Rose- prans Hills in order that a comparison could be made (Table |14) . j I Because the residual soils contain a much higher per- I jcentage of sulphates than the transported adobe, it is pos sible that there may have been a loss during transport. | : i These salts could either have become part of the ground j i water by percolation or were lost as run-off through an : i Outlet from this low-lying area. On the other hand, inas- | t I much as sulphate content is dependent on the pH of the soil (Krumbein and Garrels, 1952, p. 15), the residual soils with a lower pH would have a greater percentage of sulphates. In other words, sulphate content increases with decreasing i pH (and Eh). The data presented in Table 14 show a corre lation of this relationship. In any event, it appears from the foregoing that depo sition within the Torrance Plain did not occur under paludal conditions. Moreover, borings have failed to disclose any peat beds or zones of high humic concentrations within the adobe blanket or at the base of this sediment. Summary ] The sedimentary study of the adobe soils indicates that 122 the transported adobe can be differentiated from residual jadobe on the basis of the clay mineralogy as determined by jx-ray diffraction studies. Furthermore, coarse fraction j jstudies indicate the provenance of the transported adobe, bther data such as consistency limits and pH are in them- i I [ selves secondary and contributory evidence. Grain size | analyses and carbon content apparently cannot be used as a ! distinguishing criterion. Field Relationships of the Adobe Soil Although the foregoing sedimentary analyses indicate that the adobe soils can be differentiated as residual or transported, their relationship to each other and to the i underlying rocks and sediments can best be delineated in the field. The geological implications of soils, aside 'from the attendant weathering processes, generally have been neglected by geologists. Much of the pedological work of i [the past is concerned with the geographic concept of soils. This concept deals primarily with specific conditions of topography, climate and vegetation as related to the forma tion of soils. ! ! j Soil development keeps pace with the physiographic changes, and in some instances, as in the case of paleo- 123 soils, is an indicator of past climates. Furthermore, ero- i jsion and deposition of the soils could be the manifestations | ;of minor orogeny which all too often is not preserved in the j jgeologic record. j Residual soils I j I Adobe.— Most of the Palos Verdes Hills is covered with a blanket of adobe soil generally less than 4 feet thick. The isoil profile consists of a well developed "A" horizon rest ing directly upon the parent rock (Figs. 15, 16, and 17). The "B" horizon is not present except locally where it may be preserved along faults. Locally, the "C” horizon is well developed, especially on the Altamira Shale. It is an i inescapable conclusion that the adobe clays have developed i I by weathering of underlying rocks. The writer, however, does not wish to imply that all the adobe soils in the Palos Verdes Hills are residual. i |Many of the larger valleys and arroyos contain valley fill consisting of an admixture of adobe and rock fragments and discontinuous layers, lenses, and tongues of poorly strati fied beds of rock fragments intermingled with adobe soil. i Much colluvial soil of similar composition also occurs on the steeper slopes (Fig. 18). Where deposition and erosion 124 I l Fig. 15.— Adobe overlying diabase basalt of the Altamira Shale. Residual adobe soil is 2 feet thick. (See X-ray sample series 104, Table 1.) Undulatory contact is due to soil talus and not to differential weathering. Exposure in road cut along Hawthorne Ave nue on the fourth terrace. Rubble is not preserved on the terrace surface. Note the weathered appearance of the basalt. 125 Fig. 16.— Adobe overlying the Valmonte Diatomite. Note the uneven contact between the residual soil and the underlying diatomite, indicating differential weath ering of the rock. Inclusion of rock fragments within | the soil is not evident at the contact. Soil thickness is 2.7 feet. Fig. 17.— Adobe overlying the Altamira Shale. Note inclusions of shale fragments in the adobe soil, indi cating its residual nature. The contact of the soil is highly irregular due to differential weathering of the shales. Thickness of soil is about 3 feet. Fig. 18.— Colluvial soil. Two distinct colluvial soil layers which "dip" towards the viewer's left are present. Exposure is in a roadcut along Crenshaw Boule vard looking east. 128 in the larger valleys have ceased due to inactive or altered jdrainage patterns, the valley fill in places occasionally i displays a newly created but poorly developed "A" and 1 1 B" i i jhorizon overlying an "A" horizon adobe. i j i The on-slope residual soils are subject to a slow. j . i (imperceptible, downs lope movement or creep facilitated be- j cause the adobe is expansive. The attendant volume changes i ■ which occur seasonally are of such magnitude as to cause jshrinkage cracks several inches wide and several feet deep |to develop at the ground surface during periods (summer) of meager rainfall. As these soils absorb moisture during iperiods of rainfall (winter), the soils swell and the cracks Iclose. In the process of swelling and closing, a downslope j movement of the soil particles occurs. Because of this creep phenomenon, adobe soils are Ifound covering beach gravels (Fig. 19) which in turn floor, i in places, wave-cut terraces. Similarly, rubble (Fig. 20) I f which rests on the platform is also blanketed with adobe soil. The exact boundaries of residual or transported soil, i for the most part, on the Palos Verdes Hills cannot be ac curately delineated. From the numerous auger borings, road cuts, and excava tions examined, it appears that no soil other than adobe Fig. 19.— Adobe soil covering beach gravels. Adobe soil, the result of creep, overlies beach gravels which consist of well-rounded, pebble to cobble size clasts resting on the wave-cut platform comprised of basalt on the fourth terrace. The fifth terrace is at the skyline. View looking north along Palos Verdes Drive South near Marineland. Beach gravels thin to the viewer's right. 130 Fig. 20.— Adobe soil covering rubble. Transported adobe soil, the result of creep, overlying rubble which rests on the truncated bedding of limestone in the Alta- I mira Shale on the second terrace south of Palos Verdes Drive South near Marineland. The rubble is comprised i of both angular and rounded cobbles and boulders. 131 ever formed on the Miocene and Jurassic rocks. If this were not the case, then evidence of such soil should be present f i jeither in the Torrance Plain as a transported deposit or within the larger valleys on the Palos Verdes Hills. I The adobe soil capping the Dominguez Hill is of minor jareal extent as compared with that of either the Palos 1 Verdes or Baldwin Hills. A well developed soil profile j jconsisting of an "A" zone approximately 2.5 feet thick rest ing on a "B" horizon varying in thickness from 2 to 6 feet is common. The underlying ”C" horizon consists primarily Of dark reddish brown {10 R 3/4), sandy, poorly indurated sediments of presumably Upper Pleistocene age. This reddish color is reflected by the residual adobe. The zonation ■leaves no doubt as to the residual nature of the soil. The I west flank of the hill displays no adobe. Probably, none was ever formed as the nearest transported adobe soil within i -the Torrance Plain does not display the typical reddish i ! polor or the associated mineralogy. Furthermore, inasmuch j las the east flank of the hill is drained by a large gully, l j it is believed that any adobe that was eroded was carried in this direction and concomitantly removed by the southward flowing Los Angeles River. Careful reconnaissance of this jarea failed to disclose any surface indication of 132 transported adobe soil. Adobe soil capping the Rosecrans Hills is also consid- ! ■ered to be residual as indicated by the zonal character of i I jthe soil relative to the underlying sediments. These soils i [are relatively thin, seldom exceeding 3 feet in thickness, i i except in those areas where the soils are considered to be c ‘ transported deposit occurring in draw bottoms in the south westerly and westerly portion of the hills. These draws have been the paths through which adobe was transported to jthe Torrance Plain. The adobe soils capping the Baldwin Hills are inter preted as residual on the basis of well-developed zonal horizons. The "A" horizon seldom exceeds 2 feet in thick- i iness, the "B" varies from 2 to 5 feet thick, and the transi tion zone or "C" horizon grades downward imperceptibly into ithe relatively unweathered Pleistocene sediments. The "B" horizon often contains pebbles of the same petrologic com- i [position of that of the "C" horizon. Much of the higher I elevations of the Baldwin Hills have been denuded of adobe and these areas expose silts and fine sands of the under lying sediments which display either no soil or a poorly developed "A" horizon, indicating the recentness of soil formation as well as erosion. The northern portion of the 133 hills display deep valleys and these are floored with transported adobe as much as 15 feet thick. No zonation, 'however, is discernible in these latter deposits. The i i southerly slopes lack an adobe cover; presumably it has since been eroded. The valley in which the present route |of La Brea Avenue north of Manchester Boulevard travels is | [floored with a blanket of adobe soil indicating the direc- i jtion of transport of these soils . ' j i As is the case on the Palos Verdes Hills, no other | i * j jsoil underlies the adobe on either the Dominguez Hill, Rose- crans Hills or Baldwin Hills. Other residual soils.— The alluvium underlying a portion i jof the Gardena-Torrance area is overlain by a residual, [reddish (5 YR 3/4 to 5 R 3/4) illite clay loam which attains a maximum thickness of 4.0 feet. The "A" zone is well de veloped and is usually 3.0 feet thick; the "B" horizon i [varies in thickness from 0.5 to 1.0 foot. This soil is [termed the Yolo clay loam by Nelson and others (1919). Overlying the clay loam is a blanket deposit of transported adobe soil. Soils developed on the Upper Pleistocene sediments (Palos Verdes equivalent) reflect the underlying sediment 134 type; the soils are either loams or silty sands of the Ramona Series. These soils are residual, seldom attaining jnore than several feet in thickness, and they usually dis play a well developed "A" horizon and a poorly developed i I"B" horizon. The "C" horizon is most conspicuous at the j jheads of valleys where deep weathering has occurred. These Isoils are overlapped in places within the Torrance Plain by i jtransported adobe. I The surface of the older sand dunes displays a residual jsoil, the Oakley fine sand, which consists of a well devel oped "A" horizon up to 3 feet thick. The "B" horizon may be totally lacking and where present, seldom exceeds 1 foot ;in thickness. I j Age.— In the Palos Verdes Hills where the adobe covers the beach gravels which rest on the terraces, a Recent age ■is indicated. On the bedrock surface, however, the residual j jadobe could be in part of Late Pleistocene age if one con- i jsiders the possibility that the adobe soil began to form ! soon after emergence of the hills. Hence, samples of the adobe at the bedrock interface were collected for palyno- logical examination. i Eight samples were examined by Mr. Gyula Kiss of the 135 Palynological Laboratory of Richfield Oil Corporation. He jstated: i i | The samples were barren of pollen and spores except for j sample 103. This sample contained a few pollen grains | of the genus Chenopodium of the Chenooodiacea family and | some grains of the genus Ambrosia of the Compositae I family. These plants belong to a group commonly known | as "sage brushes" and the pollen grains found are of j recent origin and no significance can be attached to i their presence. i Although no actual C ^ dating was attempted on samples of the residual adobe soils, from discussions with members i ! jof Dr. Libby's staff of the University of California at Los Angeles it was concluded that dating could not be accom plished because of the low carbon content of the soils. [Furthermore, there would be no assurance that dates obtained j jwould be correct because of inherent contamination of the soils by plant and animal remains. Because the upper 45 feet of sediments in the younger i portion of the Torrance Fan contains reworked adobe soil jand because the adobe overlying the Yolo clay loam is a i transported deposit, the Yolo clay loam is older than the i i younger portion of the fan. There is no way to determine conclusively what the age relationship of the residual soils are to each other. How ever, it is postulated that the soils developed on the Upper I 136 Pleistocene sediments, the Ramona Series, are older than the Oakley fine sand; and in turn the Oakley fine sand is older than the residual adobe. I l i I [Transported adobe j The boundaries of transported soils are usually marked by contacts which may be designated overplaced and under- i placed (Butler, 1959, p. 14). The overplaced contact is \ | lone in which two soils are separated by deposition; the j iyounger soil overlies the older soil. An underplaced con- i [tact is one in which two soil layers become separated by i 'erosion, the older soil appears to "run off into the air" i [and disappears, and the younger soil appears below it. The relative position of the soil, therefore, indicates its j priority in time. The former illustrates the simple and 'self-evident principle of the Law of Superposition. The [latter can be said to be analogous to a regressive overlap ! |or off-lap. I i Adobe remnants.— That the adobe was transported from the Palos Verdes Hills northward to the Torrance Plain is evi denced by the Torrance Fan. That the adobe soil was trans ported from the fan to the Harbor City area can be determined by tracing the ground surface adobe within the [confines of a northeasterly trending stream valley to an l f 'elevated adobe remnant which overlies Upper Pleistocene pediments. The surface of these sediments underlying the ! ' ' ladobe displays an "A" and "B" horizon silty sand soil. I (Although the soil map shows the adobe as isolated patches, l the adobe is doubtless continuous throughout the stream I [valley bottom. Much of this channel has been filled for tract housing. Thickness of the adobe in the stream bottom 1 ivaries from 8 to 12 feet. i j The adobe remnant is about 20 feet topographically higher than the stream channel. The adobe soils comprising i [the remnant are relatively thin, seldom exceeding 3 feet in j thickness and are deeply weathered. This anomaly can be j explained either by assuming the adobe to be residual or [that uplift has taken place since the deposition of the adobe. The sedimentary analyses as presented earlier leave | [little doubt as to the provenance of the adobe. Further more, the existence of an older soil underlying the adobe ! ! shows its depositional character. Therefore, uplift must have occurred subsequent to the deposition of the adobe. The remnant occupies the crest of the Torrance Anticline. According to Crowder (1956), the anticlinal structure was 138 ,«» * initiated in Late Miocene time. One can conclude, there fore, that the structure was growing since its inception. Although no definite connection could be established between the adobe remnant paralleling Sepulveda Boulevard [with that along the Pacific Coast Highway, the ground-sur- j jface of the adobe as mapped indicates that very likely there was a connection and that it has subsequently been eroded. jThe relationship of the adobe to the underlying Upper I iPleistocene sediments indicates the adobe is a transported ! deposit and not a residual soil. This adobe occupies a Sportion of the surface expression of the Wilmington Anti- icline. As is the case with the Torrance Anticline, the jWilmington structure has grown in Late Recent time. i A portion of Gaffey Canyon which flows southward to jSan Pedro Bay is partially floored with adobe containing !shale fragments. It is believed that this deposit was de prived directly from the Palos Verdes Hills by means of i . [westerly flowing canyons and arroyos which empty into Gaffey jCanyon. There does not seem to be any physical connection with the Wilmington adobe remnant to that of Gaffey Canyon, j It is of interest that in Gaffey Canyon buried adobe j occurs. Approximately 2 to 3 feet of silts and fine sands overlie the adobe within the channel bottom. These covering 139 sediments are being derived from active erosion of the Pleistocene sediments at the headward portion and walls of |the canyon. Torrance Plain.— The Torrance Plain contains the largest i t jareal extent of transported adobe soil. A two-pronged con- 1 nection from the Harbor City and Sepulveda Boulevard remnant ! adobe bodies to the Torrance Plain exist. These connections I represent stream channels that were elevated because of up- i jlift of the aforementioned anticlines. i i The Torrance Plain may be subdivided into 3 areas i dependent upon the provenance of the adobe. The largest i body is that portion southeasterly of the adobe ground- jsurface constriction near Hawthorne. It is postulated that i this extensive body of adobe was derived from the Palos jVerdes Hills except for that portion in the northeastern i part that more likely received adobe from the erosion of I the Rosecrans Hills. The area northwest of the constriction i i jreceived most of the adobe from the Baldwin Hills through i i stream channels now represented by elevated adobe remnants. Undoubtedly, some intermingling or transfer of adobe from both north and south occurred at the constriction. I The adobe along the eastern and southern periphery of 140 the largest body laps onto sediments of Upper Pleistocene and Recent age. Along the western periphery, the adobe laps onto older stabilized dune sand, Recent in age. Borings in I i I [the center of this presently low-lying area encounter adobe i ! [underlain by fine-grained alluvium which overlies Upper i Pleistocene deposits. ! ; "A" and "B" horizon soils of the Ramona Series con- ! i sisting of silty sands and loams are well developed on the | Upper Pleistocene sediments and the overplaced contacts ileave no doubt as to the transported character of the adobe. i i The adobe of the Torrance Plain displays similar physi- I cal characteristics of the parent adobe of the Palos Verdes Hills. Shrinkage cracking is better developed, the cracks i » being larger and deeper than those of the residual soils j ! only because the adobe is thicker. Cracks are wedge-shaped, j i may be as much as 4 inches in width at the surface decreas ing in width with depth, and extend to 5 or 6 feet, the I I [depth being limited by the thickness of the deposit. For jthe most part shrinkage cracks are randomly oriented. How- i ever, those that form first may be subparallel. As shrink age continues, secondary and tertiary cracks form that [either intersect or abut into the primary ones. Polygonal development as in typical mud cracking is not apparent. 141 Shrinkage cracking is related to the water or moisture con- jtent of the soil. As the water content of the soil is re- I t Iduced below the plastic limit, the soil assumes a semi-solid condition. As further drying takes place, the soil mass i ! [eventually attains a solid state at which point further i i jshrinkage wi'll not occur. The water content needed to fill [the soil voids under this condition is termed the "Shrinkage i I [Limit." This is the water content below which a reduction lin moisture will not cause a decrease in the volume of the ] 1 jsoil mass. During periods of rainfall, the cracks close because of the increased moisture content and closure begins i ;at the surface and continues downward as percolation of rainfall increases with depth. The shrinkage cracks are [not self-perpetuating; that is, they do not form at the same i i i place seasonally. J | Swell characteristics of the two soils are also simi- jlar. In montmorillonite clays, the structural elements, [silica and gibbsite, are arranged in a 3-layer system con sisting of 2 silica sheets separated by a hydrated alumina sheet (Scott, 1963, p. 40). The forces holding the layers together are of the oxygen bond type which are weak com pared with those between kaolinite (hydrogen bond) layers. Thus, water molecules can enter between the montmorillonite 142 sheets, causing strong swelling characteristics. In illite clay, the same structural elements occur except that potas sium ions bond the sheets together, causing a much stronger lattice resulting in a lesser swell tendency than montmor- jillonite. Sodium montmorillonites are much more susceptible ito swell than montmorillonites containing calcium. Expan sion tests conducted in the laboratory show that adobe soils jexert swell pressures up to 4 tons per square foot, i Maximum thickness of the adobe in the Torrance Plain j joccurs within the center of this depressed area and from jbore hole data is up to 12 feet thick. When the thickness of residual adobe on the Palos Verdes Hills is compared with that of the transported adobe of the southern portion of the Torrance Plain, one cannot but wonder what the total thick- i I ness of the residual soils were to account for this mass of i transported adobe. Casagrande (1936) proposed an empirical 1 method for the graphical determination of the preconsolida- i Ition load, that is, the determination of the greatest pres- j sures under which a clay has been consolidated during its past geologic history. The compression of a soil occurs primarily as a function of a decrease of the volume of voids. Thus, if the voids in a soil are entirely filled with water, compression that can be measured occurs as a 143 result of the escape of waters from the voids. Gradual compression of a soil, such as the overburden weight of the soil per se. is termed consolidation. Most of the early studies on consolidation were performed on marine clays that had not been subjected to seasonal variations in moisture. In such clays, the preconsolidation load closely approxi- j imated the weight of the overburden and it could usually be I jshown that the excess corresponded to the weight of sedi- i tnents which had been removed by erosion. Later Studies on ] - ■ jsoils, however, show that much of the preconsolidation load i i jcould be attributed to compressive forces which acted on i ithe soil during drying. New investigations reveal that high i lvalues of preconsolidation load can also be attributed to i chemical action (Tschebotarioff, 1951, p. 103). Consolida tion characteristics of the residual and transported soils were determined and the curves are depicted in Figures 21 i - ■ I jand 22 respectively. The preconsolidation load of the re- ! jsidual soil is calculated to be 3.7 tons per square foot. i j The dry densities of the soil were determined to be 100 lbs/ cu.ft. Hence, the thickness of the residual soil indicated by this empirical method is 74 feet. On the other hand, the preconsolidation load for the Torrance Plain adobe in dicates a thickness of 36 feet. Because these latter soils PRE-CONSOLIDATION LOAD CONSOLIDATION CURVE PALOS VERDES HILLS ADOBE in >- 20 LOAD - T O N S /S Q .F T . 24 FIGURE 21 1 4 4 CONSOLIDATION CURVE TORRANCE PLAIN ADOBE P R E - CONSOLIDATION LOAD 20 L O A D -T O N S /S Q .F T . 100.0 10.0 FIGURE 22 146 are a transported deposit, the preconsolidation load must be attributed to either drying or chemical action Or both. Nonetheless, if one considers the latter thickness as being the excess preconsolidation load, then the thickness of the i (residual soil is 38 feet. Considering that 10 feet of soil | i jhas been preserved along a fault, the thickness of the (residual soil determined by this method is within the realm 1 j |of possibility. There is also a possibility that a portion iof the preconsolidation load of the residual soil may be (inherited from the parent sedimentary rock. i Inasmuch as the field evidence indicates that no other j (type of soil formed on the bedrock surface of the Palos Iverdes Hills, the adobe must, therefore, indicate soil for- ) Imation under one particular climatic condition. The fresh- i ,ness of the deposits on the younger portion of the Torrance i (Fan indicates that the climate was not much different from i 1 Ithat of the present Mediterranean type. I The poor sorting of the fan deposits suggests that j much of the deposition was by mudflow; and that the well- to moderately-sorted adobe within the Torrance Plain indi cates deposition by stream flooding from stream valleys or channels as they emptied into the depressed area. Under natural conditions, the pre-adobe surface was 147 probably very poorly drained. Drainage was to a depression pr downwarp between Hawthorne and Torrance. This area is the site of a thick accumulation of alluvial silts and clays yhich overlie Pleistocene sediments. Standing water must i have remained for long periods of time as both the trans ported adobe and the underlying alluvial deposits would | inhibit percolation. Penetration of rainwater and water f jfrom surface runoff through these deposits is slow. Coeffi- I bients of permeability for the sediments are extremely low, i j ranging from 0.5 feet per month to 0.01 feet per month. Thus, according to Poland and others (1959, p. 12), the haturally inferior quality of the shallow water in the iSardena area is related to this undrained depression. | The adobe in the northwestern portion of the Torrance Plain is similar to that of the southern portion in physical jcharacteristics. The thickest section of adobe appears to be restricted to that area just northwest of the constric- i jtion where bore holes have encountered adobe up to 15 feet thick. The sediments underlying the adobe consist of older 3une sand and Upper Pleistocene sediments comprised of interbedded sands, silts and gravels which on the periphery o f the basin display well-developed "A" and "B" soil hori zons. Whereas the southern portion of the Plain contains, 148 in part, underlying alluvial deposits, these deposits are lacking in the northern portion. Isolated areas of older i jdune sand and Pleistocene deposits which existed as highs i - ■ i when the adobe was deposited protrude through the adobe I blanket. j l i I Other adobe remnants.--Those adobe remnants westerly of i the constriction overlie older dune sand on which "A" and ! i !"B" silty sand soil horizons are developed. These remnants ! 'occupy local topographic depressions which are approximately I ; 2 to 5 feet below the surrounding countryside and are swales i developed on the surface of the older dune sand. These i i ;swales, which are about 0.2 mile in width, may have been j i jchannels for the transfer of the adobe sediment between the i {two basins . i The relationship of the adobe remnants between the larger expanses of residual adobe on the Baldwin and Rose- jcrans Hills is not clear. Because it is a totally developed ■j area consisting of residential neighborhoods, there was no opportunity for exploration. Inasmuch as the remnants occupy topographic highs along the Newport-Inglewood Uplift, they are probably residual, being the non-eroded adobe occupying the crests of the Potrero and Inglewood Anti- 149 clines. i | The adobe north of Inglewood occupies a south-draining jvalley on the present route of La Brea Avenue. This valley i ' . i jwas doubtless one of the paths of the transported adobe from I jthe Baldwin Hills to the Torrance Plain. The valley bottom I Icontains alluvium overlain by adobe. I ! The "arrowhead"-shaped expanse of the adobe west of jlnglewood (Plate II) is residual, having developed on the i Isurface of the underlying Upper Pleistocene sediments. A' i Iconnection can be shown extending from this area to the deposited adobe of the northern extremity of the Torrance i Plain by means of several isolated elevated remnants of transported adobe. i i ! The adobe remnant southwest of Compton is a transported i deposit. The adobe overlies alluvium, composed of fluvial sands, and "A" horizon loams that comprise the north flank lof Dominguez Hill. In view of the black color and clay jmineralogy of the adobe, its source was undoubtedly the residual adobe capping the Rosecrans Hills. Deposition could have been by the ancestral Compton Creek. BaIlona Gao.— Inasmuch as the adobe occupying the gap bottom is underlain by Recent alluvium, there can be no 150 doubt as to its transported nature. A portion of the adobe was derived from the Baldwin Hills and the remainder from the Santa Monica Mountains by streams that drain its south ern slopes. X-ray diffraction studies indicate that the residual adobes from these 2 sources are montmorillonitic, | I jand therefore it is not possible to determine the amounts leach source contributed. The adobe along Washington Boule- I jvard is separated artificially from the main adobe deposit t by the paved channel of Ballona Creek. The expanse of adobe inorthwest of the Baldwin Hills was not mapped in its entire ty, as this adobe reflects deposition from a source indica- j Itive of a physiographic division not included in the present i is tu d y . i I Thickness of the adobe within the gap varies from 3 to I j & feet and in most instances the thickest adobe reflects ^deposition within narrow distributaries that were developed fc>n the alluvial surface. | Age.— The transported adobe represents the latest cycle . of alluviation that'has occurred in the area of study in Late Recent time except for those deposits in Gaffey Canyon which overlie the transported adobe. 151 Drainage patterns For the most part, the main drainage systems within the area of study since the end of the Pleistocene epoch was in a westerly or southerly direction, discharging into Santa jMonica or San Pedro Bays. ! | The stream transporting the adobe from the Torrance Fan 1 I ito the Torrance Plain was in a northeastern direction and j i ithis stream had its course altered by the growth in Recent i itime of the Torrance Anticline so that the stream flows | isouth into Bixby Slough, which was evidently a part of j jGaffey Canyon which discharges into San Pedro Bay. Uplift | !along the Gaffey Anticline caused the upper reaches of this i j |stream channel to be blocked, forming the present landlocked i i jdrainage basin. j The present ephemeral drainage has been superimposed |on the post-Palos Verdes deformational surface. Compton Creek drains an area of about 30 square miles north of Dominguez Hill and east of the Rosecrans Hills. In the 1890's, the creek maintained a course along the west side of Dominguez Gap and discharged southward into San Pedro Bay. The creek is now paved and joins the Los Angeles River near its intersection with Del Amo Boulevard. 152 The most important stream in the northern portion of the study area is Ballona Creek, whose tributaries drain the southern slopes of the Santa Monica Mountains and the north ern part of the Baldwin Hills. The stream discharges di rectly into the Playa del Rey Marina, Centinela Creek, which drains the south and southwest slopes of the Baldwin jHills, flows northwestward and discharges through a paved I jchannel into Ballona Creek. Prior to the integration of r jdrainage by the Los Angeles County Flood Control District, j } Centinela Creek maintained a course parallel to Ballona ] | jcreek along its south margin, emptying into the low coastal marshes. i Drainage of the southern portion of the Torrance Plain I i ! was to the downwarp north of the city of Gardena. The area i jsouthwest of Gardena drained to Laguna Dominguez. Most of i i ithis drainage has been integrated by the paved Dominguez i jchannel and discharges into the East Basin Channel of Los I jAngeles Harbor. j j Bixby Slough was and is still receiving sediments from a well-developed drainage area, about 70 square miles, draining the Harbor City and Wilmington areas; and in time this landlocked basin will become filled. Most of the tributary streams leading to the slough are being filled by 153 placement of fill ground for housing developments. A simi lar situation prevails for the drainage system discharging into Laguna Dominguez. I i i RECENT-PLEISTOCENE BOUNDARY Reade's (1872) definition of the Recent epoch as that time interval since the beginning of the last major rise in sea level does not apply to the area of study. The incising j jof both Redondo and Santa Monica Canyons must have occurred i Iprior to the rise of sea level. It might be argued that the i t |rise in sea level was a contributory factor in the back- Ifilling of the landward segment of Redondo Canyon. If this j i jis true, then the landward segment of Santa Monica Canyon jwould have become backfilled also. This is not the case. I Furthermore, according to Reade1s definition, the incising of the canyons would have occurred in the Late Upper Pleis- ! jtocene and the backfilling in the Recent. The stratigraph- I iic relationship of the Gardena Aquifer to the Upper Pleis- j I tocene sediments indicates backfilling took place in the Recent. The beginning of the Recent epoch, therefore, should not be delineated by a major rise in sea level but by the withdrawal of the-Late Upper Pleistocene sea. The Upper 154 155 Pleistocene was a time of marine deposition, at least within the area of study, whereas the Recent epoch is a period of degradation and continental deposition. Furthermore, along with the withdrawal of the sea, the beginning of the Recent is marked by uplift; otherwise, the Upper Pleistocene sedi ments could not have been subjected to erosion as the record i i i 'indicates . I j Thus, the end of the Pleistocene epoch is marked by j jthe deposition of the Palos Verdes Sand in the Palos Verdes jHills and its stratigraphic equivalent within the south western portion of the Los Angeles Basin. Marine deposits younger than the Palos Verdes Sand, excluding those that are F jcurrently being deposited along the shore, do not exist in | i jthe area of study. The fossiliferous marine deposits which occur on the higher terraces on the Palos Verdes Hills are older than the Palos Verdes Sand. From the foregoing, one must conclude that the Recent epoch reaches back further in time than heretofore supposed. Shepard (1956) assigned an approximate interval of 15,000 years since the beginning of the Recent epoch. It appears that this time span may be of too short duration to account for the fluvial history of the area. What the length is in years is unknown, and will remain so until such time that 156 organic material which can be isotopically dated is avail able . i RECENT MOVEMENT That the Recent epoch is not a period of quiescence is shown by sediments of Late Upper Pleistocene and Recent age which are folded and faulted. Moreover, the implications of jthe transported adobe soils indicate the recentness of j icontinual uplift. The Recent uplift of the Baldwin Hills j |as well as of the other structures along the Newport- I i llnglewood Fault zone cannot be disputed in light of the i I Ifluvial history undergone by the ancestral Los Angeles iRiver. The history of Ballona Gap further indicates that jthe Recent epoch is a time of structural instability. More- ! lover, recent major earthquakes, the Inglewood earthquake of ! j !1921 and the Long Beach earthquake of 1933, attest to the i ! slate crustal instability of the area. j The writer does not intend to discuss the Recent structural history of the region, as it is beyond the scope of this paper. A comprehensive treatment of the Pleistocene structural history of the north border of the Palos Verdes Hills relative to the basin geology is given by Woodring and 157 158 others (1946). The relationship of the ground water hydro logy to the Newport-Inglewood Fault zone is discussed by jPoland and others (1959) . SUMMARY The study of the geology and sediments of the south western portion of Los Angeles County has resulted in the following salient factors: i i I | 1. The southwestern portion of Los Angeles County is i junderlain by marine sediments of Late Upper Pleistocene age i (which heretofore were mapped as terrace deposits. These | jsediments, the unnamed Upper Pleistocene deposits, are the | Istratigraphic equivalent of the Palos Verdes Sand which l Irests on the youngest marine terrace of the Palos Verdes |Hills. i The Late Upper Pleistocene sediments represent !shallow lagoonal, tidal or near-shore deposits from varying source areas and were deposited under rapidly changing con ditions. The upper portion of the deposits is predominant ly fine-grained, consisting of sand, silt and clay, whereas the lower part is mainly sand containing some gravel and subordinate amounts of silt and clay. Along the coast, 159 16 0 these deposits, which attain a maximum thickness of 560 feet, are divided into 3 zones: the lower Redondo Tight zone, the overlying Merged Silverado zone and an upper zone, the Manhattan Beach Aquiclude. In the Gardena Syncline extending through Gardena northwest to Inglewood, the "200- ! jfoot sand" is the stratigraphic equivalent of the Redondo i fright zone. I 5 The Recent-Pleistocene boundary is marked by the i j withdrawal of the Pleistocene sea and accompanying uplift. i ! The Upper Pleistocene marks the end of marine deposition, | whereas the early Recent is a time of degradation and flu- j ivial deposition. I 2. A subaerial origin and a Recent age is indicated i for Redondo and Santa Monica Canyons. The ancestral river that incised Redondo Canyon deposited the Gardena Aquifer. i jSanta Monica Canyon was incised by the ancestral Los Angeles i River. 3. A nonmarine terrace cover, Pleistocene to Recent in age, is comprised of poorly sorted to unsorted rubble and crudely stratified gravelly sands which either overlie ma rine deposits of Pleistocene age which in turn rest on the wave-cut platform or overlie the platforms per se of the 13 marine terraces of the Palos Verdes Hills. The terrace i ______________________________________ __________________ _ 161 cover represents talus, slope and rill wash, fan detritus and landslide material which for the most part accumulated after emergence of the terraces. In some instances, how ever, rubble was deposited prior to emergence, j 4. Deposits of Recent age comprise sediments indica tive of lagoonal and littoral environments as well as those \ |of eolian and fluvial origin. I i j The Gardena Aquifer, a coarse-grained fluvial i deposit which extends inland from Redondo Beach across the I Newport-Inglewood Uplift within the confines of the wind gap between the Rosecrans Hills and Dominguez Hill, was deposit- led by an ancestral westward flowing river that incised its i i !channel into the post-Upper Pleistocene deformational sur- i face. j | Underlying Dominguez Gap and extending southward jto San Pedro Bay, the Gaspur Aquifer, which consists of I sand and gravel, was deposited by an ancestral San Gabriel River in Recent time. The upper fine-grained phase of the aquifer may have been deposited by the Los Angeles River. The petrology of the "50-foot gravel" indicates that this deposit, which underlies Ballona Gap, was deposit ed in part by Centinela Creek, which drained the north slopes of the Baldwin Hills and by the several streams that 162 drained the south slope of the Santa Monica Mountains. Interdistributary and blanket peats which overlie the grav els indicate that a positive change in elevation resulting from subsidence and/or an eustatic change in sea level occurred in the Late Recent. A belt of stabilized dunes, aligned ridges and ihills parallels the shoreline from Ballona Gap to the Palos j jVerdes Hills and extends inland to overlap the Torrance r |Plain. Sediments comprising these hills and ridges consist j {of a weathered and partially cemented dune sand underlain i I by non-cemented dune sand; an intermediate zone of terrace I {deposits; and a lower horizon comprised of beach sands and 'gravels. Active dune sands which occur in a narrow strip {extending from Ballona Gap southward to Redondo Beach over- | jlie the older stabilized dune sand. 5. Alluvium that underlies the central portion of the Torrance Plain was deposited by the Los Angeles River as a {flood-plain deposit prior to uplift along the Newport- Inglewood Fault zone. The Torrance Fan, which is along the toe of the low foothills of the Palos Verdes Hills, is comprised of an older portion occupying approximately the eastern quarter of the feature and a younger portion which in turn consists 163 of two coalescing fans having a common apron or toe. The i jtopography of the western portion of the younger fan indi- 1 cates that subsidence has occurred since deposition. ! 6. Surface adobe soils of the area are both residual i land transported and can be so differentiated on the basis of ! 1 i i jclay mineralogy and coarse fraction analyses, as well as by j j I field relationships. The transported adobe soil represents j | I ithe latest major cycle of alluviation of the region. X-ray diffractometer studies show that the adobe j . j soils of the Palos Verdes Hills are comprised of montmoril lonite. The clay fraction in the underlying rocks of the ■ i Monterey Formation is also comprised of montmorillonite, indicating the residual character of the adobe soil. The alluvial clays which underlie the adobe soil in the Torrance Plain contain montmorillonite, illite and i kaolinite. Inasmuch as the adobe soil contains only mont morillonite, the soil could not have formed from the weath ering of the underlying alluvium. Furthermore, the over- placed contacts leave little doubt as to the depositional i nature of the adobe soil. It is believed that the adobe soils of the Torrance Plain are a transported deposit de- i rived from the erosion of the residual adobe of the Palos t J yerdes Hills, Rosecrans Hills and Baldwin Hills. 164 Adobe soils on the highs along the Newport- Inglewood Uplift are also residual as indicated by X-ray diffractometer studies of both the soils and underlying Upper Pleistocene sediments. ’ Residual soils developed on the Upper Pleistocene l I ideposits, the Ramona Series, are older than the residual j i [soils, the Oakley fine sand, developed on the older sand jdunes. These soils in turn are older than the residual 'adobe soil. I 7 . Late crustal instability of the area is shown by [deposits of Upper Pleistocene and Recent age which are i i folded and faulted. i i i ! i REFERENCES i REFERENCES |Barshad, I., 1950, The effect of interlayer cations oji the j expansion of the mica type of crystal structure: Am. | Mineralogist, v. 34, p. 225-238. j i iBeeking, B., Kaplan, I., and Moore, D., 1960, Limits of the ! | natural environments in terms of pH and oxidation re duction potentials: Jour. Geol., v. 68, p. 243-284. I i i \ [Bradley, W. F., Grim, R. E., and Clark, W. L., 1937, A study I of the behavior of montmorillonite upon wetting: Zeitj | & Krist., v. 97, p. 216-222. i _ ! i ; SButler, B. E., 1959, Periodic phenomena in landscapes as a ■ | basis for soil studies: Com. Sci. Indust. Org., Aus- | tralia, no. 14, p. 1-20. i ; Bureau of Reclamation, 1960, Earth manual: U. S. 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A., 1956, Effect of heat on vermiculite and mixed-layered vermiculite-chlorite: | Am. Mineralogist, v. 41, p. 899-914. j i : jWillet, G., 1937, An Upper Pleistocene fauna from the Bald- ; win Hills, Los Angeles County, California: Trans. San | Diego Soc. Nat. Hist., v. 8, p. 379-406. 1 Willis, R., and Ballantyne, R. S., 1943, Potrero oil fields: | Geologic formation and economic development of the oil and gas fields of California: Calif. Dept. Nat. Res., ! j Bull. 118, p. 310-317. Winterburn, R., 1943, Wilmington oil field: Geologic for- ! mations and economic development of the oil and gas | fields of California: Calif. Dept. Nat. Res., Bull. ! 118, p. 301-305. I ; iWissler, S. G., 1943, Stratigraphic formations of the pro- ! ducing zones of the Los Angeles Basin oil fields: Geologic formation and economic development of the oil ! | and gas fields of California: Calif. Dept. Nat. Res., : j Bull. 118, p. 209-234. ! i jWoodrmg, W. P., Bramlette, M. N., and Kew, W. S. W., 1946, j Geology and paleontology of the Palos Verdes Hills, California: U. S. Geol. Survey Prof. Paper 207, 145p. 118 ° 20' 118 ° 10 ' RBCtJfT AND UPPER PLEISTOCENE SEDIMENTS or THE SOUTHWESTERN PORTION or LOS ANGELES COUNTY, CALIFORNIA by Joseph Frank Riccio 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 (Geology) June 1965 n s ^ o ' 1 I 8 ° 2 0 ‘ B A LD W I N HILLS 1 8 ° IO ‘ UJ Or I cn Uj Uj < S > O DOMINGUEZ HILL O Q V o 5 M I L E S 1 __ 1___ 118 ° 3 0 ' PHYSIOGRAPHIC FEATURES OF PORTION OF LOS ANG PLATE X ' c\ co Uj LU CD C O O, O DOMINGUEZ HILL o Q 5 M I L E S R I C C l O 1965 FEATURES OF THE SOUTHWESTERN OF LOS ANGELES COUNTY P LA TE X 1 10° 30' 1 10 ° 20’ S L A U S O N 130 V / V )> Inglewood M A N C H E S T E R o Hawthorne LU R O S E C R A N S o X . LU Torrance LEGEND X-RAY DIFFRACTION SAMPLE tto. LIMITS OF ADOBE SOIL R E S ID U A L I I t r a n s p o r t e d too C O A S T 1 1 8 ° 2 0 ' b l v d . b l v d a v e . SLAUSON Inglewood M ANCHESTER A VE V - " m Hawthorne I izt L U ROSECRANS AVE. Compton Gardena v . S T la C E L U L O a. Torrance BLVD. H W Y C O A S T o > 33 Hawthorne > I ^ % is*m t/' r~>ii-v— LT\ *.'39 R O S E C R A N S I — t / 4 < Torrance LEGEND • X-R AY DIFFRACTION SAMPLE LIMITS OF ADOBE SOIL I -IT ;] R E S ID U A L [ ] TRANSPORTED Iio. C O A S T toe .toe 5 M IL E S 110° zo' I i B ° 3 0 ' AREAL DISTRIBUTION OF ADOI SOUTHWESTERN PORTION OF L PLATE 31 o _l CD Hawthorne UJ R O S E C R A N S A V E . Compton H 3 • U4 Gardena i — S T lu t r UJ c n U J Torrance ^ b l v d . 1 09 H W Y C O A S T L J tO € OS 5 M IL E S R IC C IO 1 1 0 ° 2 0 ' IUTION OF ADOBE SOIL IN THE. PORTION OF LOS ANGELES COUNTY PLATE 31 118 ° 30' 118 ° 20' SEDIMENTARY ROCKS IQ o M a l l u v i u m m A C T IV E O U N E S A N D O L D E R O U N E S A N D R E C E N T I5 S 7 1 P A LO S V E R D E S F O R M A T IO N fQ p u l U N N A M E D P L E IS T O C E N E D E P O S IT S B B S SAN P E D R O F O R M A T IO N U P P E R G AFF£Y ANTiCt-iNC LOW ER 118° 20 118° IO P = to o 4 W f F f Y ANTlCi-lN£ 33? 50 o " p * C P ■ pv LEGEND S E D IM E N T A R Y ROCKS P L E IS T O C E N E ■ p l i o c e n e M IO C E N E l Q ° ' l A l l u v i u m ■ B a c t i v e O U N E S A N D L 9 * ° I O L D E R D U N E 5 A N D l.a h « l P A l O S V E R D E S F O R M A T IO N l o p o l U N N A M E D p l e i s t o c e n e d e p o s i t s t g g p j S A N P E D R O F O R M A T IO N H R R E P E T T O F O R M A T IO N M O N T E R E Y F O R M A T IO N IGNEOUS A N D M E TA M O R P H iC R C C t\S M IO C E N E J U R A S S IC B A S A L T F R A N C IS C A N F O R M A T IO N 1 " /OOS 0 0 5 0- - .'WLELif b T ..... 1 SvACUtfr S77?L/CTtWE F A U lT I M S * < f O w h E R E a p p r o x i m a t e I C O N C E A L E D F A U L T A N T lC L J N E f D A S H E D W H E R E A P P R O X I M A T E , S O T T E D W H E R E C C N C E A - E O } 5 1’ N C L IN E { D A S H E D W H E R E A P P R O X I M A T E t D O T T E D W H E R E C O V C E & l E O ) CONTACT { O A S H E D L A N D S liO E W HERE A P P R O X I M A T E } • F U S S lL L O C A l IT V - - 1 G E O L O G r A D A P T E D FROM S T A T E uses o r C A ^ i F O W R B U L L P R O F P A P E R 2 0 ? iQ A I 118° 30 118° 20 AREAL GEOLOGY OF PORTION OF LOS THE ANGEL PLATE HI t 0 0 2 '004 GAFFtY ANTIC syncun f a R iC C lO >965 18 20 ie° io Y OF THE SOUTHWESTERN F LOS ANGELES COUNTY PLATE 3H 725 H 724 A 713 B PACIFIC Qso Qso 7 0 3 D 704 D 702 K 705 & Qsr Qsr H * L l J U J c c < / > CD OLDER SAND DUNE 725 H 726 D 725 J RICO 12 726G Qso 716 J 705B ' 717 C b a y SCALE ; I" = 2000' SUBSURFACE G E < J — U J U J a: t - OLDER DUNE SAND SAND P L A T E H L UBSURFACE GEOLOGY OF REDONDO - HERMOSA BEACH AREA Qsr ACTIVE DUNE SAND Qso OLDER DUNE SAND CROSS - SECTION LE G E N D FILL M GRAVELLY SAND 1 I SAND SANDY SILT SILT CLAY SCALE : 1 = 9 0 0 Horiz. l" = 150' Vert. M -3 FOR AM ZONE 7 0 4 D W E LL N U M B ER CJ o < _ > cc to C \ J SAND 702 K c c . L lI CD SAND DUNE OLDER b e a c h MANHATTAN m e r g e c M -3 U i Z > z UJ w JO > < t SAND d u n e OLDER GRAVEL SAND BEACH MANHATTAN BEACH AQUICLUDE MERGED SILVERADO ZONE M-3 REDONDO TIGHT ZONE SAN PEDRO SAND m D U N E S A N D O L D E R S A N D DEPOS BEACH TERRACE AQUI FER GARDENA JJDE MANHATT ZONE SILVERADO MERGED M - 3 ' ONE TIGHT M-3 M - 3 SAND PEDRO SAN Q < 3 - O r- SAND GRAVEL 3UICLUDE ZONE ZONE sand M-3 m in O N UJ n e LU > < < t n o 5 q: L a J X T A A \ M-3 GARDENA REDONDO AQ TIGHT ZONE 726 D C v ! SAND DEPOSITS BEACH SAND a g r a v e l AQUICLUDE MANHATTAN BEACH M -3 ! GO O - ICO 1 - 200 — - 300 - 400 4- -500 -GOO - 700 IOO SAND DUN E OLDER M A N H A TTA N BEACH AQUICLUDE AQUI FE R - 100 ZONE SIL V E R A D O M E R G E D ----200 M-3 Z O N E — - 3 0 0 M - 3 LU 3 UJ 3 Z UJ LU 1 3 O uj UJ SA D U N E O L D E R BEACH GRAVE SAND M AN HATTA N BEACH M ER G ED AQUI M-3 SILV E R A D O Z O N M -3 REDONDO T IG H T S A N P E D R O SAN d a t a FR O M LOS A N G E LE S C O U NTY f l o o d c o n t r o l d i s t r i c t B£DONOO_ M-3 M-3 SAND PEDRO SAN UJ < < <A O SAND GRAVEL GARDENA CLUDE Z O N E TIGHT M-3 R E D O N D O Z O N E M-3 A N D M-3 I- ■ M -3 B 4 0 0 -500 ■ 600 700 ~3 — OLDER SA N D DUN E MANHATTAN BEACH AQUICLUDE AQUI FE R MERGED SILVERADO ZONE M-3 ZONE — 100 o ----100 200 - 3 0 0 - 4 0 0 - 5 0 0 6 0 0 - - - 7 0 0 R IC C IO 1965 118° JO i i8°JO BALLONA AQUIFER GARDENA AQUIFER LEGEND LINES OF EQUAL ELEVATION ON THE BASE OF THE AQUIFERS 1 1 8 ° 2 0 SUBCROP LIMITS OF BALLONA, GA SHOWING RELATIONSHIP OF SANTA f PLATE : GARDENA AQUIFER 5 0 ' ' GASPUR AQUIFER 5 M il e s AD APT ED FROM STAT E OF C A L I F O R N I A D*ft. B u l L 104 RiCCiO '9 6 5 .ONA, GARDENA AND GASPUR AQUIFERS ' SANTA MONICA AND REDONDO CANYONS PLATE 2!

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Asset Metadata

Creator Riccio, Joseph Frank (author)

Core Title Recent And Upper Pleistocene Sediments Of The Southwestern Portion Of Losangeles County, California

Degree Doctor of Philosophy

Degree Program Geology

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

Tag Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Stone, Richard O. (committee chair), Chilingar, George V. (committee member), Gorsline, Donn S. (committee member), Merriam, Richard (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-179924

Unique identifier UC11359238

Identifier 6509982.pdf (filename),usctheses-c18-179924 (legacy record id)

Legacy Identifier 6509982.pdf

Dmrecord 179924

Document Type Dissertation

Rights Riccio, Joseph Frank

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