A gravity and magnetic study of the Tehachapi Mountains, California

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Content A GRAVITY AND MAGNETIC STUDY OF THE TEHACHAPI MOUNTAINS, CALIFORNIA by Jeffrey B. Plescia A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (Geological Sciences) August 1985 UMI Number: DP28573 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI DP28573 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest' ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES, CALIFORNIA 90089 Ph.D. Ge, ?12Q 3/3 I This dissertation, written by Jeffrey B. Plescia under the direction of h is. Dissertation Committee, and approved by all its members, has been presented to and accepted by The Graduate School, in partial fulfillm ent of re quirements for the degree of D O C T O R O F P H IL O S O P H Y Graduate Studies Date DISSERTATION COMMITTEE Chairperson Yean of ABSTRACT The magnetic field over the Tehachapi Mountains exhibits only a few anomalies, being influenced largely by anomalies in the San Joaquin Valley and Mojave Desert. Plutonic and metamorphic rocks have low remnances and low magnetic susceptibilities. Only the granodiorite of Claraville induces a large magnetic anomaly because of its high susceptibility relative to the other rocks. The Tehachapi Mountains display a gravity high juxtaposed between the gravity lows of the San Joaquin Valley and Mojave Desert. This high results from the high density of the metamorphic rocks exposed in the southwest part of the range and the thick sections of low-density sediments in adjacent regions. The Garlock-Pastoria fault system and the White Wolf fault are characterized by long- wavelength gravity gradients resulting from the crustal- scale density contrasts across these faults. Several local gravity anomalies occur within the range and can be related to the geology. Positive anomalies occur over some of the metasedimentary pendants in the northeastern part of the range but not in the southwest. Modeling indicates that the bulk density of the pendants increases northeastward because of a decrease in carbonate content and an increase in the amounts of clastic and volcanic material. Tertiary volcanic and clastic rocks northeast of Tehachapi Valley display a negative gravity anomaly due to the low density of the material. Profile gravity data were modeled to determine the regional crustal structure of the area. Modeling indicates that the crust beneath the Tehachapi Mountains is approximately 35 km thick, 5-7 km thicker than beneath the San Joaquin Valley or Mojave Desert. The crust thickens gradually rather than abruptly at the edges of the range. Within the range, the crust is modeled as being composed of three major layers and some near-surface lenses. The Tehachapi Mountain crust represents an upended cross section through the Sierra Nevada batholith. The structural level of exposure increases southwestward through the Tehachapi Mountains, from a few kilometers in the northeast part of the range to tens of kilometers in the southwest. The high-density deep crustal layer which represents the base of the batholithic complex is absent from the Tehachapi Mountain section. This section of the batholith has been removed by the thrusting of the Pelona schist and oceanic crust beneath the batholithic complex during Mesozoic subduction. The Tehachapi Mountains appear to be in regional isostatic equilibrium. Modeled crustal columns indicate the pressure at 50 km in the range and in the adjacent San Joaquin Valley and Mojave Desert averages 1.454 GPa. Each crustal column is within 2% of that average. A 35 km thick crust is also consistent with expectations based on topography. Isostatic anomalies over the range vary from -10 to +15 mgal. ACKNOWLEDGMENTS I would like to thank Tim Fogarty for providing the computer programs which allowed the computational aspects of this study to be completed. I would also like to thank Tom Henyey for his continued support through many years and the members of my committee, Greg Davis, Charlie Sammis and Darrell Judge, for helpful suggestions. The cooperation of the people at the Tejon Ranch Company, especially Mr. Duncan Paddy, and the Bear Valley Springs Community Services District, especially Mr. Jack Geary, is greatly appreciated. The Southern California Edison Company, the Tehachapi Cummings Water District, and the California Water Resources Agency provided elevation data which allowed gravity measurements to be made in numerous locations where they would otherwise not be possible. I would also like to thank a whole cast of characters, too numerous to mention individually, who provided physical and moral support during field work. V TABLE OF CONTENTS PAGE ABSTRACT .................................................... ii ACKNOWLEDGMENTS ............................................ v INTRODUCTION ............................................... 1 GEOLOGY ..................................................... 4 A. PLUTONIC ROCKS SOUTH OF THE G ARLO CK-P AS TO RIA FAULTS ............................................... 7 1. GRANITE OF TEJON LOOKOUT .................... 7 2. BIOTITE GRAN ODIORITE OF GATO-MONTES ........ 8 3. BIOTITE GRANODIORITE OF CAMERON ............. 9 4. GRANITE OF BEAN CANYON ...................... 9 5. BIOTITE GRANODIORITE OF LEBEC ............... 10 B. PLUTONIC ROCKS NORTH OF THE GARL OCK-PASTORIA FAULTS ............................................... 11 1. BIOTITE GRANODIORITE OF CLARAVILLE ........ 11 2. GARNETIFEROU S GRANITE OF TEHACHAPI AIRPORT. 12 3. PINK GRANITE OF BISHOP RANCH ................ 13 4. HORNBLENDE BIOTITE TONALITE OF BEAR VALLEY SPRINGS ........................... 13 C. METAMORPHIC TERRANE NORTH OF THE GARLOCK-PASTORIA FAULTS ........................... 14 D. PELONA SCHIST ...................................... 17 E. METASEDIMENTARY ROCKS ............................. 21 F. TERTIARY VOLCANIC AND CLASTIC ROCKS ............ 26 STRUCTURE ................................................... 33 A. REGIONAL CONTEXT ................................... 33 B. FAULTS ............................................... 40 1. WHITE WOLF FAULT .............................. 40 2. GARLOCK FAULT .................................. 43 3. PASTORIA FAULT ................................ 47 4. PINON HILL AND LITTLE OAK CANYON FAULTS ... 50 5. TYLERHORSE AND COTTONWOOD FAULTS............. 50 6. TEJON CANYON FAULT ............................ 51 C. THE VALLEY SYSTEM ................................. 52 MAGNETICS ................................................... 54 A. DATA COLLECTION AND REDUCTION ................... 54 B. RESULTS .............................................. 56 1. GENERAL COMMENTS .............................. 56 2. SAN JOAQUIN VALLEY ............................ 60 3. BEDROCK OF THE TEHACHAPI MOUNTAINS ......... 60 4. TERTIARY ROCKS NORTHEAST OF TEHACHAPI VALLEY .............................. 65 5. ANTELOPE VALLEY ............................... 67 6. PENDANTS ........................................ 69 7. THE INTERMONTANE VALLEYS ..................... 73 C. SUMMARY .............................................. 7 4 GRAVITY ..................................................... 77 A. DATA COLLECTION AND REDUCTION ................... 77 B. GRIDDING AND FILTERING ........................... 80 C. MODELING ............................................ 82 vi i D. RESULTS .............................................. 83 1. GENERAL COMMENTS .............................. 83 2. SPECIFIC ANOMALIES ............................ 88 a. METAMORPHIC TERRANE ...................... 88 b. GRANITIC ROCKS SOUTH OF THE GARLOCK AND PASTORIA FAULTS............................ 90 c. PENDANTS .................................. 92 d. TONALITE OF BEAR VALLEY SPRINGS ........ 97 e. TERTIARY ROCKS NORTHEAST OF TEHACHAPI VALLEY ...................... 98 f. ANTELOPE VALLEY........................... 100 3. FAULTS .......................................... 101 a. GARLOCK-PASTORIA FAULT SYSTEM .......... 101 b. WHITE WOLF FAULT.......................... 102 4. THE INTERMONTANE VALLEYS .................... 103 a. BEAR VALLEY ............................... 104 b. CUMMINGS VALLEY ........................ 106 c. BRITE VALLEY ............................. 107 d. TEHACHAPI VALLEY ........................ 108 E. VERTICAL DERIVATIVES .............................. Ill F. UPWARD CONTINUATION ............................... 113 G. CRUSTAL MODELS ..................................... 114 1. METHODOLOGY .................................... 114 2. REGIONAL IMPLICATIONS ........................ 120 3. LOCAL IMPLICATIONS ........................... 125 a. TEHACHAPI PROFILE ....................... 125 vi i i b. TEJON CANYON PROFILE ..................... 127 c. PASTORIA CANYON PROFILE ................. 128 4. GEOLOGIC CROSS SECTION ALONG THE TEJON CANYON PROFILE ................................. 129 5. DISCUSSION OF MODEL RESULTS ................ 136 H. SUMMARY OF GRAVITY RESULTS ....................... 138 SUMMARY ..................................................... 145 REFERENCES .................................................. 149 TABLES ...................................................... 172 ILLUSTRATIONS ........................................... 178 APPENDICES .................................................. 242 APPENDIX I GRAVITY DATA ................................. 243 APPENDIX II DETAILS OF THE COLLECTION AND REDUCTION OF GRAVITY DATA ........................................ 262 ix INTRODUCTION The Tehachapi Mountains of southern California form a topographic and structural transition zone between the crystalline batholith terrane of the Sierra Nevada to the northeast and the San Emigdio Mountains-Coast Range terrane to the west. Several of the largest and most active faults in California, the San Andreas, Garlock and White Wolf faults, lie within or adjacent to the Tehachapi Mountains. Within the Tehachapi Mountains, north of the Garlock- Pastoria faults, gneissic and granoblastic rocks are widespread and the metasedimentary pendants are highly metamorphosed when compared with the pendants of the Sierra Nevada (Ross, 1980, 1983, 1985a). As a whole, these rocks represent a deeper crustal level than is currently exposed in the Sierra Nevada proper. Igneous and metasedimentary rocks south of the Garlock-Pastoria faults are more akin to those currently exposed in the Sierra Nevada. Geophysical studies (gravity, magnetic, and seismic refraction) combined with surficial geologic mapping have led to a fairly detailed understanding of the crustal structure of the Sierra Nevada batholith. A considerable amount of geologic data have been compiled for the Tehachapi Mountains and the geologic history of the range is finally beginning to be understood. Geophysical data, however, are largely reconnaissance in nature. Though 1 regional studies of the gravity and magnetic fields have been made, seismic refraction data are completely lacking. Hence, the crustal structure of the southernmost Sierra Nevada is poorly understood. The purpose of this investigation is to develop an understanding of the crustal structure of the Tehachapi Mountains through analysis of potential field data. Relevant questions to be addressed include: (1) what are the characteristics of the gravity and magnetic field; (2) what does the gravity data indicate in terras of crustal thickness, the presence of a root and isostasy; (3) what is the structure of small-scale crustal features (pendants and plutons); and (4) what types of boundaries are the White Wolf and Garlock-Pastoria faults? In order to understand the crustal structure, gravity and surface magnetic data were collected and combined with existing data to provide a potential field data base adequate for interpretation. To quantify aspects of both the local and regional crustal structure the gravity data was analyzed in terms of gravity modeling programs. These programs, referred to as 2V2 D modeling programs, allow the individual crustal bodies to be extended to finite, rather than infinite, distances normal to the model profile. Following chapters deal with the geology and structure of the Tehachapi Mountains, the collection and reduction of the potential field data, and an interpretation of that 2 data in terms of its implications for crustal structure. Since the gravity data were analyzed in a quantitative manner through filtering and modeling, a more thorough discussion of its implications is possible than for the magnetic data. The magnetic data was not modeled and can be discussed only in qualitative terms. 3 GEOLOGY The Tehachapi Mountains of southern California are the southwestern extension of the Sierra Nevada batholith terrane. Forming a east-northeast-trending bedrock ridge, the Tehachapi Mountains separate the Antelope Valley, with an average elevation of 750-900 m, from the San Joaquin Valley, which has an average elevation of 100-250 m. Elevations within the range increase from 1200 m east of Grapevine Canyon to more than 2100 m south of Tehachapi Valley and decrease to 1500-1700 m north of the valley. Topography within the range is rugged with steep-sided canyons and precipitous mountain fronts. The intermontane valleys, Tehachapi, Cummings, Brite, and Bear Valleys, have average elevations of 1200 m. For purposes of orientation, Figure 1 shows the geographic features referred to in the text. Studies of the geology of the Tehachapi Mountains have been both reconnaissance and detailed in nature. The first regional synthesis (Buwalda, 1954) reviewed the existing knowledge of the geology and structure of the range. Subsequently, several studies were completed allowing the more detailed regional compilations of the Bakersfield and Los Angeles 1:250,000 map sheets (Jennings and Strand, 1969; Smith, 1964). More recently, Ross (1980, 1985a) has incorporated significant new information with previously published data to produce a geologic map and detailed analysis of the basement rocks of the Tehachapi Mountains. Several 15' quadrangles which lie completely or largely within the mountains have been published. These quadrangles include; Cummings Mountain (Dibblee and Warne, 1970), Tehachapi (Dibblee and Louke , 1970), Lebec (Crowell, 1952), Willow Springs and Rosamond (Dibblee, 1963), Neenach (Wiese, 1950), Breckenridge Mountain (Dibblee and Chesterman, 1953), and Elizabeth Lake (Simpson, 1934). More recently, Dibblee (1973 a,b) has compiled preliminary maps of the Grapevine and Pastoria Creek 7 sheets. Studies of various local geologic problems have also been made by Turner (1928), Harris (1950), Smith (1951), Lloyd (1957), Michael (1960), Michael and McCann (1962). Additional studies have been made of the geomorphology of the intermontane valleys (Lawson, 1906), the western Tehachapi Mountains (Sharry, 1981), Western Mojave Desert (Dibblee, 1967), the southern and southeastern San Joaquin Valley (Bartow, 1984; Bartow and Doukas, 1978; Hoots, 1930) and the metamorphic and plutonic basement of the Tehachapi Mountains (Ross, 1983, 1985 a,b). The Tehachapi Mountains are dominated by both igneous and metamorphic rocks. Sedimentary and volcanic rocks occur along the flanks and in isolated patches within the range. Figure 2 is a generalized basement geologic map of the Tehachapi Mountains based on Ross (1980). Basement rock 5 units described here are taken from Ross (1980, 1985a) who has presented the only detailed geologic map of the region as a whole. The Tehachapi Mountains can be broadly divided into four areas based on the bedrock geology. Along the length of the range south of the Garlock-Pastoria faults, the granitic plutonic rocks and metasedimentary pendants represent shallow crustal levels (Haase and Rutherford, 1975). North of the Garlock fault and northeast of Tejon Canyon toward Lake Isabella, the plutonic rocks and metasedimentary pendants have come from intermediate crustal levels (Ross, 1985 a,b; Elan and Thomas, 1984). Southwest of Tejon Canyon and north of the Garlock-Pastoria faults is a zone of highly metamorphosed rocks which represent deep crustal levels (Sharry, 1981). Finally, an elongate schist body, the Pelona schist, occurs between the north and south branches of the Garlock fault. Unmetamorphosed volcanic and sedimentary units occur extensively north of Tehachapi Valley and alluvium fills the valleys. Unmetamorphosed sediments also occur along the margins of the range in the San Joaquin and Antelope Valleys. 6 A. PLUTONIC ROCKS SOUTH OF THE GARLOCK—PASTORIA FAULTS Plutonic rocks of the Tehachapi Mountains south of the Garlock-Pastoria faults include the granite of Tejon Lookout, the biotite granodiorite of Gato-Montes, the biotite granite of Cameron, and the granite of Bean Canyon (Figure 2). In addition, several large metasedimentary pendants occur within these plutons. These rocks form an irregular bedrock ridge (<10 km wide) extending northeast from the San Andreas fault toward Cache Creek Canyon near the town of Mojave. All of the plutonic rocks are truncated to the north by the Garlock or Pastoria faults and are overlain southward, in the Mojave Desert, by alluvium. 1- GRANITE OF TEJON LOOKOUT The granite of Tejon Lookout, the westernmost pluton, extends discontinuously eastward from the San Andreas fault to the Tehachapi Willow Springs Road. Petrologic studies by Ross ( 1985a) indicate the rock is composed of 28% plagioclase, 37% potassium feldspar, 32% quartz and 3% - 8 biotite and has a bulk density of 2.61 0.02 g cm • It is generally medium- to coarse-grained except near contacts where it is fine-grained. Crowell (1952) and Wiese (1950) noted that several facies were present, the most common being massive and medium-grained. Numerous pendants of Bean 7 Canyon metamorphic rocks occur within the granite of Tejon Lookout (Figure 2). Wiese (1950) argued that the geometric relations of the pendant margins indicate that those margins represent the original intrusive roof. 2. BIOTITE GRAN ODIORITE OF GATO-MONTES Extending discontinuously between Cameron and the San Andreas fault is the biotite granodiorite of Gato-Montes (Figure 2). Wiese (1950) and Dibblee (1967) mapped it as a quartz diorite, although Ross (1985a) has termed it a granodiorite. The rock is generally medium- to fine grained, although it is locally porphyritic having scattered mafic inclusions. Ross (1985a) noted the granodiorite is composed of plagioclase (52%), quartz (24%), potassium feldspar (12%), biotite (10%) and hornblende (2%). It has a bulk density of 2.67 _+_ 0.03 g cm o . Several samples of the granodiorite have been dated using Rb/Sr methods and indicate an age of approximately 85 m.y. (R.W. Kistler in Ross, 1985a). The Gato-Montes, though generally homogenous, does exhibit a foliation near its contact with the granite of Tejon Lookout. Ross (1985a) suggests that the Gato-Montes is intruded along its margin by the granites of Tejon Lookout and Bean Canyon and that the hornblende diorite bodies mapped in the area by Dibblee (1967) are zones of contamination rather than distinct intrusions. 8 3. BIOTITE GRANODIORITE OF CAMERON The biotite granodiorite of Cameron crops along the south side of the Garlock fault between the Tehachapi Willow Springs Road and Cache Creek. It is coarse-grained compared with adjacent plutons. Similar to the other plutonic rocks, the granodiorite of Cameron is composed of 47% plagioclase, 17% potassium feldspar, 24% quartz, 9% biotite and 3% hornblende and has a bulk density of 2.65 _+ _ o 0.01 g cm . Contacts with the adjacent plutons are hidden and the pluton is covered along its eastern and southern margins by younger (Pliocene) sediments of the Horned Toad Format ion. 4. GRANITE OF BEAN CANYON The granite of Bean Canyon is exposed in several small masses within the granite of Tejon Lookout near Bean Canyon. Detailed mineralogic information was not presented by Ross (1985a) but he noted that the rock was composed of about equal amounts of plagioclase, potassium feldspar, and quartz. Ross suggested that the granite of Bean Canyon may be a felsic differentiate of the granite of Tejon Lookout. 9 5. BIOTITE GRANODIORITE OF LEBEC Although it occurs north of the Garlock fault, the biotite granodiorite of Lebec is petrologically similar to other rocks south of the fault, hence it is included here. Occurring primarily west of Grapevine Canyon, the pluton extends only a short distance eastward into the study area. It is truncated by the Garlock fault on the south and by the Pastoria thrust fault on the north. The granodiorite of Lebec initially was termed a quartz monzonite by Crowell (1952). Petrologic studies of the rock indicate it is composed of 50% plagioclase, 13% potassium feldspar, 25% quartz, 12% biotite and 1% — 3 hornblende and has a bulk density of 2.67 _+_ 0.02 g cm . Crowell noted two facies, a dominate fine-grained facies and a subordinate coarse-grained facies. Slickensides and shearing are common throughout the rock, particularly near the San Andreas and Garlock faults. One Rb/Sr age of 85 m.y. is reported in Ross (1985a). The rock bodies described above are similar to the batholithic rocks of the Sierra Nevada. They are medium- to coarse-grained, have low densities and exhibit little or no pervasive metamorphic fabric. The Bean Canyon metasedimentary pendants, like those in the Sierra Nevada farther north, are only mildly metamorphosed. Geobarometric 10 analyses suggest that the plutons and metamorphic rocks south of the Garlock fault represent crustal depths of only a few kilometers (J. Sharry, 1984 , personal communication; Haase and Rutherford, 1975). B. PLUTONIC ROCKS NORTH OF THE GARLOCK—PASTORIA FAULTS The plutonic rocks of the Tehachapi Mountains north of the Garlock-Pastoria faults can be divided along the 118° 30' meridian into two groups based on the percentage of mafic minerals, bulk density and textural fabric (Figure 2). Westward of that meridian, a single pluton, the hornblende-biotite tonalite of Bear Valley Springs dominates. The area to the east is characterized by smaller and more numerous plutons which include the biotite granodiorite of Claraville, garnetiferous granite of Tehachapi Airport and the pink granite of Bishop Ranch. 1. BIOTITE GRANODIORITE OF CLARAVILLE The biotite granodiorite of Claraville is exposed discontinuously both north and south of Tehachapi Valley (Figure 2). In overall outcrop area it rivals the tonalite of Bear Valley Springs, but most of its exposure is north of the study area. Northeast of the valley the granodiorite is covered by Tertiary volcanics, replaced by other plutons 1 1 or metamorphic rocks. The granodiorite is composed of 51% plagioclase, 14% potassium feldspar, 23% quartz, 11% biotite and 2% hornblende, and has a bulk density of 2.68 _ O 0.03 g cm • Dibblee and Louke (1970) mapped the unit as a hornblende-biotite quartz diorite. They noted that it was massive to faintly gneissoid or foliated and locally contained elongate, dark-colored xenoliths whose long axis lies parallel to the foliation orientation. Rb/Sr ages determined for this pluton indicate ages of approximately 90 m.y. whereas K-Ar dates on biotite give younger ages of 75-85 m.y. (Ross, 1985a). 2. GARNET1FEROUS GRANITE OF TEHACHAPI AIRPORT The garnetiferous granite of Tehachapi Airport outcrops in an isolated hill in Tehachapi Valley and in a narrow zone about 5 km wide north of the valley. It is composed of 27% plagioclase, 38% potassium feldspar, 33% quartz and 2% biotite and has a bulk density of 2.59 _+_ 0.02 _ o g cm . Intrusion of the granite has domed the metasedimentary rocks suggesting to Ross (1985a) that the present exposures are close to the original roof of the pluton. 12 3. PINK GRANITE OF BISHOP RANCH Pink granite of Bishop Ranch is exposed in a limited area in eastern Tehachapi Valley. The rock forms a high ridge on the south side of the valley and a hill at the mouth of Cache Creek. It has a density of 2.58 _+_ 0.03 g cm"" 3 and is composed of plagioclase (24%), potassium feldspar (40%), quartz (34%) and biotite (2%). The granites of Tehachapi Airport and Bishop Ranch were originally mapped as part of a widespread quartz monzonite unit by Dibblee and Louke (1970) who described it as massive and medium-grained. They reported a U-Pb date of 95 m.y. from what Dibblee (1963) considered to be a correlative rock in the Rosamond Hills in the Mojave Desert. 4. HORNBLENDE BIOTITE TONALITE OF BEAR VALLEY SPRINGS Hornblende biotite tonalite of Bear Valley Springs represents the most widespread plutonic rock in the range. The tonalite is dark, foliated and inclusion rich. Ross (1985a) noted that the rock has a "messy" texture resulting from foliation, mafic schlieren, "ghost-gneiss" areas, and abundant mafic inclusions, all of which resulted from the contamination of the tonalite by pre-existing country 13 rocks. It is composed of 53% plagioclase, 2% potassium feldspar, 22% quartz, 13% biotite and 11% hornblende, and _ o has a density of 2.74 +_ 0.04 g cm . It was originally mapped as a diorite by Wiese (1950) and a hornblende biotite quartz diorite by Dibblee and Chesterman (1953), Dibblee and Louke (1970) and Dibblee and Warne (1970). Dates (K/Ar and Rb/Sr) on the tonalite indicate ages of 80-88 m.y. (Ross, 1985a). Along Tejon Canyon, Ross (1985a) has identified a zone in which the highly metamorphosed rocks to the southwest grade into the less- to un-met amorphosed rocks to the northeast. He termed these rocks "hornblende-rich diorite to tonalite of the Tehachapi Mountains". They are composed of 55% plagioclase, <1% potassium feldspar, 10% quartz, 6% biotite and 29% hornblende. The tonalites and diorites have an average density of 2.82 _+_ 0.05. These rocks were suggested to be texturally and minerologically transitional between the dark amphibolitic rocks of the metamorphic terrane and the tonalite of Bear Valley Springs. C. METAMORPHIC TERRANE NORTH OF THE GARLOCK—PASTORIA FAULTS A belt of high-grade metamorphic rocks occurs north of the Garlock and Pastoria faults, extending southwest from Tejon Canyon to Grapevine Canyon. Ross (1985a) included this area as part of the mafic-metamorphic terrane of the 14 San Emigdio-Tehachapi Mountains and noted it included gneiss, amphibolite, granofels, and metasedimentary rocks. On a regional basis, Ross separated only the quartzo— feldspathic gneiss from the other rock types which he included in this terrane. The quartzo-fe1dspathic gneiss includes the metasedimentary rock units as well as bodies which Ross (1985a) felt may be magmatic. Within the metamorphic terrane are local zones of homogenous diorite and tonalite that appear to be magmatic. In more detailed mapping along the Garlock fault, Sharry (1981) noted five units within this metamorphic terrane: raylonite; Bison granulite; White Oak diorite gneiss; Tunis Creek garnet granulite; and quartzo-feldspathic gneiss. Ross' gneiss is a strongly foliated, dark colored, hornblende-rich rock that dominates the lithology in the metamorphic terrane. This is the same unit as Sharry's Bison granulite. It is composed of andesine (40%), quartz (<20%), hornblende (20-30%) and biotite (Sharry, 1981; Ross, 1985a). Sharry noted that the presence of coexisting ortho- and clinopyroxene indicated that the rock had undergone granulite facies metamorphism. A meta—igneous protolith was suggested by Ross for the hornblende-rich gneis s• Amphibolite is composed almost exclusively of intermediate plagioclase and hornblende. Wiese (1950) mapped much of this rock as diorite and gabbro, although 15 Ross believes it was of metamorphic origin having local zones of melting that produced homogenous textures. Massive granofels are widespread throughout the range and are composed of varying amounts of plagioclase, hornblende, quartz, biotite and clinopyroxene (Ross, 1985a). Rocks termed granulite by Ross occur in only a few locations and are characterized by the presence of hypersthene, indicative of granulite facies metamorphism. Metasedimentary rocks include impure quartzite and calc-hornfels which both Ross and Sharry termed quartzo- feldspathic gneiss. In addition to the quartz and calc- hornf els , Sharry reported the presence of marble and amphibolite. The contacts of these rocks with surrounding metamorphic rocks were not observed, but Sharry believes they were probably both structural and intrusive, forming at deep crustal levels. Along the north branch of the Garlock fault, Sharry noted small patches of mylonite. The mylonite lies between the Pelona schist, which occurs south of the north branch of the fault, and the White Oak diorite gneiss which is structurally higher. The mylonite is composed of a matrix of crushed hornblende and quartz surrounded by white plagioclase augen. Petrologic data from Ross (1985a,b) and geobarometric data from Sharry (1981) indicate that rocks of the metamorphic terrane represent a deep crustal level. Ross 16 summarized the petrologic evidence for a deep origin as follows: 1) presence of hypersthene, coarse red garnets, and brown hornblende; 2) the difficulty in differentiating between igneous and metamorphic origin on the basis of texture; 3) metamorphic grades up to granulite; 4) the occurrence of migmatites. Sharry's (1981) data for the metamorphic rocks immediately north of the Garlock fault indicate metamorphic conditions of 7.3-8.7 kbar and temperatures of 526°-631°C. Granulites farther north of the fault have been metamorphosed at temperatures as high as 850°-950°C, corresponding to depths of 26-30 km. D. PELONA SCHIST Several bodies of schist occur within the Tehachapi and San Emigdio Mountains (Wiese, 1950; Dibblee and Louke, 1967; Sharry, 1981; Ross, 1983, 1985a; Davis, 1983). In the Tehachapi Mountains, these rocks occur between the north and south branches of the Garlock fault and in Cache Creek Canyon. The rock is composed of thinly layered quartzo- feldspathic schist, and fine-grained quartzite. The main schist body, between the branches of the Garlock fault, is composed of about 75% gray albite-quartz-mica schist and 25% amphibole-albite-chlorite greenschist (Sharry, 1981; Ross, 1985a). The quartzites are 80 to 95% quartz and have 17 minor garnet, mica and feldspar. The smaller body in Cache Creek Canyon is composed of dark-gray to greenish, highly foliated albite schist in a groundmass of actinolite, biotite and epidote (Ross, 1985a). Sharry (1981) reported the only conglomerate ever observed in the Pelona schist in the Tehachapi Mountains. The conglomerate is a moderately coarse-grained, matrix supported rock composed of clasts of quartz and quartzo-fe1dsphatic rock. Within the range, the main schist body is bounded on the north side by the so-called north branch of the Garlock fault. The fault is a thrust fault which dips northward at a shallow angle and presumably correlates with the Vincent thrust (Sharry, 1981). The southern boundary of the schist is formed by the steeply-dipping south branch of the Garlock fault. The schist of the Tehachapi Mountains has been correlated by several authors (Ehlig, 1968; Haxel and Dillon, 1978) with schists that out crop elsewhere in southern California; the Pelona, Rand and Orocopia schists. The correlation is based on the numerous similarities between these various exposures including: a) the most abundant rock being a gray, quartzo-feldspathic schist; b) subordinate rock types include greenschist, amphibolite, metachert, siliceous marble and serpentine; c) distinctive porphyroblasts of gray to black albite and bright green fuchsite; d) the occurrence of thrust sheets of gneissic 18 and granitic rocks above the schist; and e) the sparse intrusion of the schist by granitic plutons. The total thickness of these schist bodies is unknown as the base has never been observed. However, up to 4 km of schist is exposed in the San Gabriel Mountains (Jacobson, 1983). Based on seismic refraction data, Malin et a 1. ( 1984) indicate that the schist on Sierra Pelona Ridge, to the southwest of the Tehachapi Mountains, may be only 1 km thick. I n t e r b e d d e d g r a y w a c k e , s i l t s t o n e a n d s h a l e a r e i n t e r p r e t e d a s t h e p r o t o l i t h f o r t h e s e s c h i s t s . T h e g r e e n s c h i s t a p p a r e n t l y r e s u l t s f r o m b a s a l t i c t u f f a n d t h e q u a r t z i t e f r o m c h e r t l a y e r s . T h e s e r o c k s w e r e d e r i v e d f r o m a c o n t i n e n t a l s o u r c e a n d d e p o s i t e d i n a n o c e a n i c e n v i r o n m e n t . The age of the Pelona schist protolith and the timing of its metamorphism is speculative. Schist and mylonite from the Vincent thrust have yielded K-Ar and Rb-Sr dates of 47-59 m.y. and a post-metamorphic quartz monzonite of Mt. Barrow has yielded a K-Ar date of 14-23 m.y. (Haxel and Dillon, 1978). These dates suggest a pre-Eocene age for the deposition of protolith and an Eocene age for the onset of metamorphism. Haxel and Dillon ( 1978) have suggested that these schist bodies formed in a Paleocene or Late Cretaceous orogenic event. They propose that the protolith was 19 deposited in an intracontinental back-arc basin and was subsequently metamorphosed during closing of the basin by overthrusting of granitic basement from the southwest. They do not believe that these schist bodies are correlative with the Franciscan schist because the Franciscan apparently has an older metamorphic age (95-109 m.y.). Burchfiel and Davis (1981) have argued that since no evidence of the rifting and collision required by the Haxel and Dillon model has been observed, that these schist bodies probably are correlative with the Franciscan metasedimentary rocks. The current exposures of Pelona schist would therefore represent local uplift of a schist body which is continuous at depth and which is connected with the Franciscan—type rocks exposed along the coast. The recent COCORP seismic reflection profile (Cheadle et a1., 1984, 1985) detected a subsurface reflector which has been correlated with the Rand thrust in the Rand Mountains. This reflector was traced south and southwest toward Mojave where it flattens into a horizontal layer at 3 sec two-way travel-time (TWTT), about 5-6 km depth. Though this data suggests that the Rand thrust, and by inference the Rand schist, continues to some depth, it does not resolve the broader questions of the correlation of the Rand schist with the Franciscan rocks, its subsurface connection with the other southern California schist bodies, or the total thickness of the schist. 20 E. METASEDIMENTARY ROCKS Pendants of slightly metamorphosed sedimentary rocks occur within the plutonic rocks of the Tehachapi Mountains. Pendant rocks on the north side of the Garlock fault, and in the southern Sierra Nevada in general, have been referred to as the Kernville Series of Miller (1931) by several authors (Buwalda, 1954; Dibblee and Warne, 1970; Dibblee and Louke, 1970; Ross, 1985a). Metasedimentary rocks south of the Garlock fault have been correlated with the Bean Canyon Series of Simpson (1934) or the Bean Canyon Formation of Dibblee (1967) (Wiese, 1950; Ross, 1985a). Pendants north of the Garlock fault are strongly elongate, trending northwest to north-northeast. South of the Garlock fault the pendants are generally elongate in the northeast direction. North of the Garlock fault, two large pendants occur at the western end of Tehachapi Valley; surrounding Brite Valley (the Brite Valley pendant) and north of Tehachapi Valley (the Tehachapi pendant). South of the Garlock fault numerous small bodies are strung out through the range. From west to east they include the La Liebre, Bronco Canyon, Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon pendants. These names are informal and are intended only to facilitate discussion of individual bodies. 21 The Tehachapi pendant is quite large and irregular in outline. Outcrops are oriented north-south and are a few hundred meters to several kilometers wide. Attitudes within the pendant strike north to north-northeast with steep (45- 80°) dips (Dibblee and Louke, 1970). Several plutons surround and intrude the pendant; the tonalite of Bear Valley Springs to the west, granodiorite of Claraville in the center and granite of Tehachapi Airport to the east. Litho 1ogically the pendant rocks consist of schist, quartzite and marble. The schist is a phyllitic schist having gneissic bands and it is fine-grained except near plutonic contacts where it is medium- to coarse-grained. It is composed of mica, quartz and, locally, plagioclase or calc-silicate minerals. Quartzite and marble occur as layers within the schist (Dibblee and Louke, 1970; Ross, 1985a). P h y l l i t i c s c h i s t a n d i n t e r l a y e r e d q u a r t z i t e a n d m a r b l e c h a r a c t e r i z e t h e B r i t e V a l l e y p e n d a n t . T h e m i n e r a l o g y o f t h e s e r o c k s i s s i m i l a r t o t h a t o f t h e T e h a c h a p i p e n d a n t . T h e t o n a l i t e o f B e a r V a l l e y S p r i n g s s u r r o u n d s t h e p e n d a n t o n a l l s i d e s . W i t h i n t h e b o d y , t h e r o c k s s t r i k e n o r t h - n o r t h w e s t a n d d i p t o t h e e a s t at a b o u t 60° ( D i b b l e e a n d W a r n e , 1970). L o c a l l y , a l o n g t h e c o n t a c t s w i t h t h e t o n a l i t e , t h e s c h i s t b e c o m e s c o a r s e - g r a i n e d a n d g n e i s s i c . Age control on the metasedimentary rocks is poor. As they are intruded by the 80-88 m.y. tonalite of Bear Valley 22 Springs (Ross, 1985a) they must be pre-Late Cretaceous. Dibblee and Warne (1970) and Dibblee and Louke (1970) consider them to be equivalent to the Kernville metasedimentary rocks (Miller and Webb, 1940) exposed farther north which are considered to be Paleozoic. South of the Garlock fault, in the southwestern Tehachapi Mountains, the dominate metasedimentary lithology is marble. To the northeast the amount of marble decreases. Simpson (1934) suggested that the steep to overturned attitudes of the rocks reflected tight folding prior to intrusion. Wiese (1950) and Crowell (1952) both noted the complex folding and faulting within these rocks. 2 The La Liebre pendant covers about 25 km and is predominately marble having a few lenses of quartzite and siliceous hornfels. An elongate body of quartz-feIds par- biotite schist and hornfels occur along the north side of the marble (Crowell, 1952). Ross (1985a) has described what he believed to be andesite flows or intrusions in the hornfels. Crowell (1952) and Dibblee (1967) noted that the attitudes within the pendant were quite irregular with strikes varying from north to west and dips of 5-50°. Crowell mapped the lower contact of the pendant as planar; the individual units cut off along this boundary. T h e B r o n c o C a n y o n p e n d a n t i s c o m p o s e d p r e d o m i n a t e l y o f m a r b l e a n d a l s o c o n t a i n s c a l c - h o r n f e l s a n d q u a r t z i t e w h i c h g r a d e s i n t o s c h i s t . L a y e r i n g w i t h i n t h e p e n d a n t s t r i k e s 23 northeast and dips at about 60° to the southeast (Wiese, 1950). Wiese noted that this body, like the La Liebre pendant, has a planar lower contact which uniformly truncates the steeply dipping beds. He suggested this relationship, in both the Bronco Canyon and La Liebre pendants, indicated the presence of a widespread, pre- intrusive thrust fault which had cut through the metasedimentary rocks. The remaining pendants to the northeast, the Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon 2 pendants, are small (3-5 km ) and lithologically and structurally different from the two large bodies to the southwest. Though marble still is present, it is not the dominate lithology. Micaeous schist, pure to impure quartzite and siliceous calc-hornfels are common. Metavolcanic rocks also occur in these bodies. Dibblee (1967) and Simpson (1934) described a metabasalt from the Bean Canyon pendant. Ross (1985a) noted the presence of an ultramafic body within the Bean Canyon pendant as well as other metavolcanic rocks in the Cottonwood, Gamble Spring and Oak Creek Canyon pendants. Ross (1985a) and Dibblee (1967) suggest these pendants extend into the enclosing plutonic rocks rather than being flat bottomed like those to the southwest. Saleeby et al . ( 1978) have noted that pendants of the southern Sierra Nevada are quite variable in lithology. 24 They found it difficult to make correlations between pendants on either a local or regional scale. Carbonate and volcanic contents seem to be the major variables. Overall in the southern Sierra Nevada - Tehachapi Mountains there is a general eastward increase in the percentage of volcanics and a decrease in carbonate. Most exposures in the southwestern Tehachapi Mountains (i.e., the La Liebre and Bronco Canyon pendants) are dominantely marble having minor quartzite, schist and hornfels (Dibblee, 1963, 1967; Wiese, 1950; Crowell, 1952). Northeastward, the percentage of elastics increases and volcanics become locally important in the form of flows and tuffs (i.e., the Bean Canyon pendant) (Dibblee, 1963, 1967). In the Saltdale quadrangle, beyond the study area to the northeast, volcanics dominate the pendant lithology (Dibblee, 1952). Simpson (1934), Wiese (1950), Crowell (1952) and Dibblee (1967) have suggested that the Bean Canyon metasedimentary rocks were Paleozoic(?) in age. However, that inference was based simply upon a lithologic similarity to Paleozoic rocks elsewhere in the southern Sierra Nevada. Diagnostic fossils have never been found in Bean Canyon pendants. Dunne e t al. , ( 1975) have suggested that the protolith for the Bean Canyon rocks was a deposit of graywackes, sand- and silt-stones and limestone and minor volcanics deposited in a Mesozoic arc—trench gap. 25 Saleeby et al . ( 19 78) have suggested that both the Bean Canyon and Kernville rocks are correlative with the Late Triassic - Early Jurassic Kings sequence of the central Sierra Nevada to the north. Ross (1985a) reported a Rb/Sr date on dacitic metavo lcanics from the Bean Canyon pendant by R.A. Fleck which indicated an age of 150 m.y. Such an age could indicate either the time of volcanism or metamorphism. Ross has interpreted the date to be the time of volcanism indicating a Late Jurassic age for the pendant which is younger than that suggested by Saleeby e t a 1. ( 1978) . F. TERTIARY VOLCANIC AND CLASTIC ROCKS T e r t i a r y s e d i m e n t a r y a n d v o l c a n i c r o c k s o c c u r a l o n g t h e f l a n k s of t h e T e h a c h a p i M o u n t a i n s b u t i n o n l y o n e m a j o r a r e a w i t h i n t h e r a n g e . T h e m o s t e x t e n s i v e o c c u r r e n c e w i t h i n t h e r a n g e l i e s n o r t h e a s t of T e h a c h a p i V a l l e y . T h e r e , t h e W i n e t , K i n n i c k , a n d B o p e s t a F o r m a t i o n s o c c u r , a l l of w h i c h a r e n o n m a r i n e a n d m o d e r a t e l y d e f o r m e d . I n t h e S a n J o a q u i n a n d A n t e l o p e V a l l e y s , T e r t i a r y r o c k s o u t c r o p i n a n a r r o w z o n e a n d r e s t u n c o n f o r m a b l y o n t h e c r y s t a l l i n e b a s e m e n t . The Winet Formation consists principally of coarse arkosic sandstone and thinner beds of sandy shale and siltstone. Sandstones predominate in the upper part and shale and siltstone dominate the lower part. It lies 26 depositionally on the Mesozoic basement and is overlain unconformably by the Kinnick Formation. The Winet is unfossiliferous, but Dibblee and Louke (1970) suggest it is correlative with the Paleocene Goler Formation in the El Paso Mountains to the east. The Kinnick Formation is distinctly different from the overlying Bopesta Formation and the underlying Winet Formation in that it is largely volcanic debris. It consists of highly colored basic volcanic tuffs and coarse agglomerates and minor basic lavas. Thickness of the formation is highly variable, ranging from 275 to more than 600 m. These thickness variations led Dibblee and Louke ( 1970) to suggest that it was deposited on a high relief surface. Mammalian fossils found in the upper part of the Kinnick indicate a middle Miocene age. The Bopesta Formation is a light-colored, variably- grained quartzose sandstone having some siltstone, ash and volcanic flows. Arkosic sandstone characterizes the upper Bopesta and the thinner lower part is composed of siltstone, sandstone and some tuff. It is about 910 m thick with the upper part being 670 m thick and the lower part about 240 m. An upper Miocene age is assigned to the Bopesta Formation on the basis of Mammalian fossils. Unnammed volcanics (lavas and pyroclastics) overlie these units in several areas and have compositions of basalt to rhyolite, porphyritic andesite being the most 27 widespread. Dibblee and Louke (1970) suggest that the bulk of the volcanics are Miocene in age, but that the youngest members could be Pliocene. Intrusive dacite and felsite occur as dikes and plugs and are probably associated with the extrusive volcanics. The plugs have been suggested to mark former eruptive vents (Dibblee and Louke, 1970). Tertiary strata are exposed along the northern margin of the Tehachapi Mountains in the San Joaquin Valley (Hoots, 1930; Buwalda, 1954; Bartow and Doukas, 1978 Bartow, 1984). These rocks occur in a narrow strip less than 2 km wide at the base of the mountain from the San Emigdio Mountains to the Tejon Hills. Tertiary rocks are not exposed at the surface along the mountain front northeast of the Tejon Hills. Several different units are present in the San Joaquin Valley along the Tehachapi Mountains. These include the Tejon Formation, Tecuya Formation, Chanac Formation, Santa Margarita Formation, Vaqueros Formation and unnamed volcanic and conglomeratic units. These rocks rest unconformably on the crystalline basement and dip at moderate to steep angles into the valley. The Tertiary section thickens from a few hundred meters in eastern outcrops to thousands of meters to the west. E a s t o f G r a p e v i n e C a n y o n , t h e T e j o n F o r m a t i o n o f Eocene age narrows and pinches out against a northwest t r e n d i n g f a u l t w h i c h l i e s b e t w e e n P a s t o r i a a n d T u n i s 28 Canyons. In the San Emigdio Mountains, west of Grapevine Canyon, a much wider zone of Tejon Formation is exposed. Along the front of the Tehachapi Mountains, the Liveoak Shale and Metralla Sandstone Members of the Tejon Formation are exposed (Dibblee, 1973 a,b). The Liveoak Shale Member is composed of siltstone, shale and some sandstone and the Metralla Member is a fine-grained sandstone. The Tecuya Formation is of Oligocene age and pinches out northeast of Tunis Canyon. Dibblee (1973 a,b) mapped two members here, a granitic sandstone and conglomerate, which dominates the section, and a subordinate granitic alluvial conglomerate. These units are overlain by volcanics and conglomerates of 01igocene(?) to Pliocene(?) age (Dibblee, 1973 a,b). The volcanics are dominated by flows of basalt, minor dacite and andesite, and tuff breccias. Unconformably overlying the volcanics are weakly consolidated alluvial conglomerates, sandstones and claystones. T h e T e j o n F o r m a t i o n i s a m a r i n e u n i t a c r o s s i t s e n t i r e l e n g t h o f e x p o s u r e . Y o u n g e r u n i t s , t h e T e c u y a F o r m a t i o n a n d c o n g l o m e r a t e d e p o s i t s a r e c o n t i n e n t a l a n d a r e e q u i v a l e n t to t h e m a r i n e S a n E m i g d i o F o r m a t i o n , P l e i t o F o r m a t i o n a n d M o n e t e r y S h a l e w h i c h a r e e x p o s e d f a r t h e r w e s t i n t h e S a n E m i g d i o M o u n t a i n s . T h i s a r e a r e p r e s e n t e d a n o c e a n m a r g i n e n v i r o n m e n t i n T e r t i a r y t i m e h a v i n g s u b a e r i a l e x p o s u r e s to t h e e a s t a n d a d e e p m a r i n e e n v i r o n m e n t to t h e w e s t . 29 In the Tejon Hills, the section has been divided into different units by Hoots (1930), Bartow and Doukas (1978) and Bartow (1984). There is little correlation of names used by Hoots (1930) or Bartow (1984) and Bartow and Doukas (1978). Based on Bartow and Doukas, and Bartow, the section includes the Olcese Sand, Round Mountain Silt, Bena Gravel, Santa Margarita Formation and Chanac Formation. At the base of the section is the Olcese Sand, a unit of variable- grained sandstones and silty-sandstone interbeds. Both the upper and lower parts of the Olcese are marine whereas the middle part is nonmarine. Round Mountain Silt is a marine section of claystone, siltstone and shale and is early Middle Miocene in age. The Bena Gravel is composed of poorly consolidated gravels, arkosic sand and sandy- siltstone and is of fluvatile origin. Pebbly sandstone and very-coarse sand compose the late Miocene Santa Margarita Formation. Uppermost in the section is the upper Miocene Chanac Formation which is composed of arkosic sandstone, siltstone, claystone and fanglomerate. Exposures of Tertiary rocks in the Antelope Valley are much more restricted than in the southern San Joaquin Valley. The widest exposures occur near the San Andreas fault in the southwestern most part of the range. There, several thousand meters of clastic and volcanic rocks outcrop from the San Andreas fault northeast for about 19 km. The section consists of marine sandstone and shale 30 overlain by nonmarine fanglomerate, gravel, sandstone, sand, shale, and clay. Crowell (1952) and Wiese (1950) referred to these rocks as upper Miocene Santa Margarita Formation and unnammed continental deposits. Dibblee (1967), however, has subdivided the section into three formations, the Quail Lake, Oso Canyon and Mecke Mine Formations. Dibblee's Quail Lake Formation is about 7 50 m thick and composed of mostly shale in the lower part which grades upward and laterally into sandstone. The late Miocene Quail Lake Formation correlates with rocks referred to as the Santa Margarita Formation by Crowell and Wiese. The Oso Canyon Formation is late Miocene in age and composed of about 1700 m of intergradational fanglomerate, conglomerate, sandstone and siltstone. These rocks were in part referred to as Santa Margarita and in part continental deposits by Crowell and Wiese. A section of fluviatile gravels and lacustrine clay about 450 m thick has been named the Mecke Mine Formation. These units are late Pliocene or early Pleistocene in age and are the Pliocene(?) lake bed deposits of Wiese. Further to the northeast along the front of the range, northwest of Mojave, is a continental deposit referred to as the Warren beds by Buwalda ( 1954) and the Horned Toad Formation by Dibblee (1967) and Dibblee and Louke (1970). The formation is exposed on the ridge separating Cache 31 Creek from the Antelope Valley. This unit is a Pliocene continental sedimentary deposit composed of friable arkosic sandstone and minor siltstone and clay. About 320 m of the formation lies unconformably on the granodiorite of Cameron (Dibblee, 1967). Pleistocene and Recent alluvial deposits cover wide expanses of the western Mojave Desert and San Joaquin Valleys. Within the range, each of the intermontane valleys is floored by alluvium. Within Tehachapi Valley an older alluvial unit, the Tehachapi Formation, has been mapped in the northwest part of the valley (Lawson, 1906; Dibblee and Louke, 1970). The unit is Pliocene or early Quaternary in age (Buwalda, 1954) and has been deformed into a southeast trending syncline which presumably underlies much of the present Tehachapi Valley. It is a fanglomerate composed of crystalline (granitic and metamorphic) and volcanic rubble and is at least 100 m thick (Dibblee and Louke, 1970). 32 STRUCTURE A. REGIONAL CONTEXT The Tehachapi Mountains exhibit a complicated structural pattern having numerous faults and folds as well as the juxtaposition of differing crustal blocks. Faults reflecting both regional and local stresses occur both along the margin of the range and within it (Figure 2). T h e n o r t h w e s t s t r u c t u r a l g r a i n o f t h e S i e r r a N e v a d a e x t e n d s i n t o t h e T e h a c h a p i M o u n t a i n s w h e r e , w i t h i n i t s c e n t r a l a n d w e s t e r n p a r t s , a d i s t i n c t c h a n g e i n o r i e n t a t i o n o c c u r s . F o l i a t i o n s a n d r e l i c t b e d d i n g i n p e n d a n t s s t r i k e n o r t h w e s t a n d d i p s t e e p l y e a s t w a r d i n t h e n o r t h e r n a r e a . W i t h i n t h e c e n t r a l a n d w e s t e r n T e h a c h a p i M o u n t a i n s t h e t r e n d s a r e m o r e e a s t e r l y h a v i n g b o t h n o r t h a n d s o u t h d i p s . S o u t h of t h e G a r l o c k f a u l t b e d d i n g w i t h i n t h e p e n d a n t s s t r i k e s n o r t h e a s t a n d d i p s t o t h e s o u t h e a s t . The change in structural trend through the range is also indicated by a deflection of the quartz diorite line of Moore ( 19 59), the ^Sr/^Sr = 0. 706 line of Kistler and Peterman (1973) and the paleocontinental margin of Ross (1983, 1985a). These various observations suggest that the Tehachapi Mountains have been rotated clockwise relative to the Sierra Nevada. 33 Rotation within the Tehachapi Mountains has been documented by Kanter and McWilliams (1982) and McWilliams and Li (1983, 1985), Kanter and McWilliams reported evidence for a 45°±14° clockwise rotation of the 80-90 m.y. old tonalite of Bear Valley Springs. They suggest that the rotation occurred between 90 m.y. (the age of the tonalite) and 20 m.y. , the age of the overlying Miocene Kinnick Formation which is unrotated. Work by McWilliams and Li (1983) on the granodiorite of Lebec, which lies southwest of the tonalite of Bear Valley Springs, suggests as much as 90° of rotation for the westernmost Tehachapi Mountains. Paleomagnetic data on tonalite of Bear Valley Springs exposed north of the White Wolf fault indicates a pole position consistent with that expected for the late Cretaceous, thus indicating no rotation (McWilliams and Li, 1983, 1985). These studies indicate that the terrane southwest of the White Wolf fault has been rotated in a clockwise sense relative to the Sierra Nevada. Davis and Burchfiel (1981) have suggested that the rotation of the Tehachapi Mountains was part of a regional episode of rotation. They propose a major right-lateral oroclinal bend of much of the Mojave and adjacent areas between mid-Cretaceous and mid-Tertiary time. Their suggested timing is consistent with that estimated by Kanter and McWilliams (1982) and McWilliams and Li (1983, 1985). 34 The change in structure across the Tehachapi Mountains is not simple and reflects motions more complicated that simple rotation about a vertical axis. Within any region the foliation or bedding attitude of the metasedimentary rocks is highly variable. A series of narrow metasedimentary pendants curve from northeast to southeast around the western margin of Tehachapi Valley. In the southwestern Tehachapi Mountains, south of Tejon Canyon and north of the Garlock fault, highly metamorphosed pendants in the metamorphic terrane have curvilinear easterly trends (Wiese, 1950; Ross, 1983, 1985a). Attitudes in metasedimentary pendants south of the Garlock fault exhibit northwest to northeast trends. The northern margin of the range is defined by the White Wolf fault between the town of Caliente on the northeast and Commanche Point to the southwest. At Commanche Point the mountain front turns southeast at a right angle but the White Wolf fault continues undeflected to the southwest across the San Joaquin Valley. Hoots (1930) suggested that the abrupt bend in the mountain front at Commanche Point resulted from a fault, which he named the Tejon Canyon fault. From the mouth of Tejon Canyon to Grapevine Canyon the mountain front again trends northeasterly. Along the section between Tejon and Grapevine Canyons, Tertiary rocks lie depositionally on the crystalline basement and no major frontal faults are 35 observed (Hoots, 1930; Buwalda, 1954 ; Dibblee, 1973 a, b; Bartow and Doukas, 1978; Bartow, 1984). Uplift of the Tehachapi Mountain block appears to have occurred both by uplift along discrete faults and by warping. As noted above, the northeastern margin of the range, between Caliente and Commanche Point, is defined by the White Wolf fault. Displacement on the fault is several kilometers up on the southside. However, to the southwest of Tejon Canyon and Commanche Point, in the southernmost part of the San Joaquin Valley, the post-Eocene rocks lie depositionally on the basement. Attitudes of these rocks vary from 20° to steeply overturned (Hoots, 1930; Dibblee, 1973 a,b; Bartow and Doukas, 1973; Bartow, 1984). These steep dips flatten with distance from the range front (M. Williams, Tenneco Oil, personal communication, 1985; Davis, 1983; Hoots, 1930). The attitudes of these rocks suggest that the front of the range between Tejon Canyon and the San Emigdio Mountains has been uplifted principally by wa rp i ng. Along the south side of the range in the Antelope Valley the Tertiary and younger rocks lie depositionally on the crystalline basement. Where they are exposed, the Tertiary rocks dip toward the desert at shallow to moderate angles and presumably flatten at depth with increasing distance from the range (Dibblee, 1967; Crowell, 1952; Weise, 1950). Several faults that trend northeast enter the 36 range at acute angles from the Mojave Desert, however, these faults are primarily strike-slip (Dibblee, 1963, 1967; Wiese, 1950), Hence, they can not be responsible for the majority of uplift which suggests that much of the uplift along the southern side of the range is the result of warping. Within the Tejon Hills, on the San Joaquin Valley side of the range, the Tertiary rocks define a west-northwest trending anticline. Numerous north-south trending normal faults and folds define a more complicated structural pattern on a local scale. The faults define a narrow, north trending horst and the folds form a series of north to northwest trending anticlines and synclines (Hoots, 1930; Bartow and Doukas, 1978; Bartow, 1984). The Winet, Kinnick, and Bopesta Formations and the younger volcanics, all of which lie north of Tehachapi Valley, have been deformed into a northeast trending syncline. Farther northeast, the syncline broadens into a basin centered beneath Cache Peak (Dibblee, 1967; Dibblee and Louke, 1970). In the sou t hwe s t e rnmo s t part of the range, in the corner between the Garlock and San Andreas faults, the Quail Lake, Oso Canyon and Mecke Mine Formations exhibit variable attitudes. Overall the units are deformed into an east-west trending syncline, but there are numerous small folds producing east-west trending anticlines and 37 synclines. Within this area, particularly adjacent to the German fault, overturned and vertical attitudes are common (Crowell, 1952; Dibblee, 1967). Buwalda (1954) suggested that the Tehachapi Mountains was a complex horst which had been elevated along both faults and steep flexures at its margins. Dibblee (1963) suggested a similar model in that the range was uplifted by compressive stresses forming a northeast trending antiformal structure. The block south of the Garlock fault was uplifted and rotated to the southeast whereas the block north of the fault was uplift and rotated to the northwest. The Tehachapi Mountains have undergone a more complex post-intrusive tectonic history than the Sierra Nevada. Whereas the Sierra Nevada have been statically uplifted along the frontal Sierra Nevada-Owens Valley fault, the Tehachapi Mountains have been uplifted along faults of varying orientation as well as warped into several folds. Additionally, the entire range has been rotated 45-90° in a clockwise sense. Uplift of the Tehachapi Mountains could have accompanied rotation of the range. If the south-dipping White Wolf fault acted as the leading edge of the rotation, deep rocks could have been uplifted to the surface by the rotational movement. The presumably overlying shallow crustal rocks would have been eroded away subsequent to uplift. The currently observed movement on the White Wolf 38 fault as well as the deformation and warping of the marginal Tertiary sediments would be due to more recent deformation possibly associated with stresses induced by the San Andreas fault. Dibblee (1967) suggested that the Tehachapi Mountain area has been subaerially exposed since 01igocene(?) or early Miocene time. That is not inconsistent with this model. An implication of this model would be that rocks north of the White Wolf fault should be unrotated. McWilliams and Li (1985) have studied plutonic rocks near the Kern River, some 30 km north of the White Wolf fault, and these rocks are determined that not rotated, consistent with this model. A more critical test, currently underway, is a study of the rocks lying immediately north of the White Wolf fault and southwest of the Edison fault. 39 B. FAULTS 1. WHITE WOLF FAULT The northern margin of the Tehachapi Mountains is delineated in part by the White Wolf fault which exhibits both left-lateral and reverse displacement. It was at the westernmost end of the White Wolf fault that the 1952 , magnitude 7.2, Kern County earthquake occurred. The fault can be traced along the base of Bear Mountain between Caliente on the northeast and Commanche Point to the southwest. Southwest, beyond Commanche Point, the fault has no surface expression as it crosses the San Joaquin Valley. However, it can be traced westward to Wheeler Ridge using well data (Davis, 1983). Seismically, the fault is defined only by a zone below which there are no coherent reflectors (M. Williams, Tenneco Oil, personal communication, 1985). Northeastward, the fault appears to merge with the Kern Canyon fault near Caliente. However, this relationship is problematic as the two faults have not been observed to connect. The Kern Canyon fault is a steeply-dipping right- lateral fault which has not been active since at least 3.5 m.y. ago (Moore and Du Bray, 1978) and the White Wolf fault is a left-lateral oblique-slip reverse fault which is still active. If the two faults are a single crustal break, then 40 the current left-lateral movement on the White Wolf fault may be either a response to local stresses or a sufficently young response to regional stresses such that left-lateral movement has not yet propagated to the Kern Canyon fault. Knowledge of the attitude of the White Wolf fault at depth comes mainly from analysis of drill hole data and studies of the seismicity associated with the 1952 earthquake. Gutenberg (1955) calculated a southeast dip of 60—66° based on first motion studies of the earthquake. Buwalda (1954) observed dips of 30-45° on faults exposed in railroad cuts excavated after the earthquake. Recent modeling of regional triangulation data by Dunbar e t a1. (1980) suggests the fault has an average dip of 60° southeast. Stein and Thatcher (1981), using both triangulation and leveling data, modeled the White Wolf fault as having three segments, each having a different attitude. Northeastward from Wheeler Ridge the strike of the White Wolf fault becomes more northerly (N73°E-N58°E- N43°E) while the dip becomes shallower (75°-35°-20°). They further suggest that the depth of faulting decreases northwestward from a maximum of 27 km to a minimum of 10 km. Thus, as the fault dip shallowed the depth of seismic activity during the 1952 earthquake decreased. Davis (1983), using well data, suggested that the White Wolf fault dips very steeply (70-80°) in the southern San Joaquin Valley southwest of Commanche Point. The shallow 41 surface dips observed after the 1952 earthquake probably represent a surficial flattening and are not representative of the dip of the fault at depth. Davis (1983) and Davis and Lagoe (1984) have speculated that the White Wolf fault was originally a normal fault and was subsequently modified into its current reverse geometry. There is, however, no direct evidence to support such a thesis. The interpretation is based soley on the rapid sedimentation rate which occurred in the San Joaquin Valley in Miocene and post-Miocene time. They believe that this high sedimentation rate requires an extensional regime and that the White Wolf fault defines the southern end of that extensional terrane. Therefore, they suggest that the fault originally was a normal fault. In order to transform a fault which presumably originally dipped northward into one that currently dips southward major crustal adjustments must occur. This could be accomplished by wholesale rotation of the crust about a east-west horizontal axis, shearing within the strata on both sides of the fault, or compression of the sediments on the San Joaquin valley side and extension on the Tehachapi Mountain side of the fault. There is no evidence to suggest any of this has happened and therefore no evidence to support the suggestion that the White Wolf fault was a normal fault in post-Miocene time. 42 The White Wolf fault might be associated with the clockwise rotation of the Tehachapi Mountains. It may be that as the range rotated, the leading edge of that rotation was marked by the White Wolf fault. Offset along the fault would increase from zero near Caliente to approximately 100 km near Wheeler Ridge, assuming 90° of rotation. During rotation, motion along the fault would bring deeper crustal levels to the surface. In this way progressively deeper rocks would be exposed farther southwest from the point of zero rotation. A cumulative offset of about 100 km, would require only a 16° dip on the fault to raise rocks from a depth of 30 km, as are exposed in the southwestern Tehachapi Mountains (Sharry, 1981). 2. GARLOCK FAULT The Garlock fault extends from southern Death Valley on the east to the San Andreas fault on the west. Cumulative left-lateral offset along the fault is approximately 48-64 km (Davis and Burchfiel, 1973). Between Cache Creek Canyon and the San Andreas fault, the Garlock fault lies within the Tehachapi Mountains and acts, as the Pastoria fault does farther west, as a major crustal boundary separating distinctly different rock types. Davis and Burchfiel (1973) describe the fault as an intracontinental transform structure which accommodates the 43 juxtaposition extensional regime of the Basin and Range against the stable Mojave block. Bird and Rosenstock (1984) have proposed a kinematic model for southern California in which they interpret the Garlock fault in a different manner. They view movement along the fault as a response to the clockwise rotation of the Mojave block relative to the Sierra Nevada block. Further, they speculate that the Garlock fault dips northward acting as a thrust fault to accomodate compression between the Mojave and Sierra Nevada blocks. Though the general aspects of the kinematic model maybe correct, the studies of focal mechanism of earthquakes along the Garlock fault by Astiz and Allen ( 1983) and the COCORP reflection data (Cheadle e t al. , 1984, 1985) do not support the suggestion of a north- dipping thrust geometry. Between Bear Trap Canyon on the west and Oak Creek Canyon on the east, the Garlock fault bifurcates into so- called north and south branches. Maximum distance between the branches is approximately 3 km. The north branch separates the metamorpliic terrane (White Oak diorite gneiss or Bison granulite) from the Pelona schist whereas the south branch separates the Pelona schist from several different granitic plutons. Both branches dip vertically where exposed (Crowell, 1952; Wiese, 1950; Sharry, 1981). Sharry (1981) believes the north branch of the Garlock fault is a thrust fault rather than being a left-lateral 44 fault as is the south branch of the fault. Sharry (1981) and Ross (1985a) have suggested that the north branch is the same fault which is exposed elsewhere as the Rand and Vincent thrusts. They believe that the north branch of the Garlock fault is an exposure of a thrust fault formed along a late Mesozoic subduction zone Astiz and Allen (1983) have studied seismicity along the Garlock fault and noted that the eastern and western segments, separated at Randsburg, have different seismic characteristics. The western segment, which lies in part within the Tehachapi Mountains, shows continuous low seismic activity and well documented creep. Several studies (Clark, 19 73 ; Guptill et al , 1 979) have documented recent vertical and strike-slip movement along both branches. Snay and Cline (1980) and C. Allen (personal communication, 1984) report geodetic data indicating current movement of several mm/yr along the south branch of the fault. First- motion studies along the entire length of the fault indicate left-lateral motion along a vertical or near vertical fault. All of the events along the fault occur above 15 km and most occur above 7.5 km. Two COCORP seismic reflection profiles cross the Garlock fault near Randsburg east of the study area (Cheadle et al. , 1984 , 1985). One line crossed northeast of Randsburg; the second crossed at the southeast end of Cantil Valley. Cheadle e t a 1. (1984, 1985) recognized two 45 zones of reflectors along the seismic line northeast of Randsburg which cross the fault apparently without offset. Each of the reflecting horizons, which occur at depths of 10 and 18-22 km, are composed of multiple, laterally discontinous reflectors extending over 0.5 to 1 sec TWTT. Using additional lines farther southwest in the Mojave Desert, they determined that these reflectors had a southwestly dip. Because the reflectors cross the Garlock fault without being offset, it was suggested that the fault extends to a depth of less than 10 km. Further, the reflector at 10 km has been interpreted as a regional detachment surface which extends northward under the Basin and Range Province. It is into this detachment surface that the range-front faults of the western Basin and Range are suggested to flatten. This would imply that the entire brittle extensional regime extended only to 10 km. A major geologic and geophysical implication of this suggestion is that all of the ranges would be truncated at 10 km by the detachment. This would imply that the root of the Sierra Nevada-White Mountain batholith should lie under the original location of the batholith, some 40-60 km farther east. However, the Sierra Nevada-White Mountain root lies beneath the ranges and is not offset, implying that these ranges carried their roots with them as they were translated westward. This is incompatible with a 46 detachment at 10 km. In order to escape this problem one might propose that the Basin and Range terrane in California was translated eastward but that would imply that the Garlock fault was a right-lateral rather than a left-lateral fault. It is interesting to note that these reflectors are dome shaped and reach their shallowest depths near Randsburg where a significant high heat flow anomaly occurs (Sass etal., 1978). In and around Randsburg the heat flow is as high as 8.3 heat flow units (H.F.U.) about four times the normal heat flow (1.5 to 2.0 H.F.U.) of the Mojave Desert (Sass e t al. , 1971; Lachenbruch, 1979 ). These reflectors may represent a thermal boundary of some sort which developed after the Garlock fault ceased activity in this region. However, the nature of these reflectors remains speculative as they are not exposed at the surface. 3. PASTORIA FAULT The Pastoria fault was first mapped by Crowell (1952) in the Lebec quadrangle. It extends westward from the intersection of the north and south branches of the Garlock fault westward through the San Emigdio Mountains to the San Andreas fault. Along its length, the Pastoria fault separates rocks of contrasting metamorphic grade in both the Tehachapi and San Emigdio Mountains. South of the fault 47 lie the granodiorite of Lebec and metasedimentary pendants whereas metamorphic rocks lie north of the fault. Exposures of the fault in the Tehachapi Mountains indicate a moderate (20-30°) southward dip for the Pastoria fault. As it approaches the Garlock fault, the dip of the Pastoria fault reportedly steepens (Crowell, 1952). In the San Emigdio Mountains, vertical to steeply northward dips are reported (Davis, 1981; Ross, 1985a). Because of its moderate southward dip, Crowell (1952) interpreted the Pastoria fault as a thrust fault. Sharry (1981) and Ross (1985a), however, have drawn different conclusions. They suggest that the Pastoria fault was originally a left- lateral strike-slip fault which more recently has been deformed into a thrust fault geometry. Crowell (1952) based his thrust fault interpretation on the geometry of the fault which placed granodiorite of Lebec (which Crowell referred to as School Canyon granite) over metamorphic rocks. Sharry (1981) and Ross (1985a) base their strike-slip interpretation on the fact that the Pastoria fault, like the Garlock fault farther east, separates rocks which have undergone different geologic histories. Geobarometric data from the Bean Canyon pendant (Haase and Rutherford, 1975), south of the Garlock fault, indicate metamorphic depths of approximately 20 km (approximately 2.5 kbar). Data from Sharry (1981) indicates the rocks 48 north of the north branch of the Garlock fault have come from depths of 26-30 km. This contrast in metamorphic grade across the faults suggests appreciable vertical movement along the Garlock and Pastoria faults. Noting that the differences in metamorphism across both the Pastoria and Garlock faults were similar, Sharry (1981, 1982) argued that the Pastoria fault originally was the western extension of the Garlock fault. This implies that the Pastoria fault, rather than the southwesternmost section of the Garlock fault, would have taken up the majority of the left-lateral displacement classically associated with the Garlock fault. Thrusting, which characterizes the latest movement, was attributed to recent reactivation by stresses associated with the bend in the San Andreas fault. Ross (1985a), however, argues that lateral movement on the Pastoria fault was earlier and that it has not been active since the intrusion of the granite of Brush Mountain. The age of the granite of Brush Mountain is uncertain but Ross (personal communication, 1985) speculates that it is probably Cretaceous in age. If that were the case, then it would indicate that the movement on the Pastoria fault occurred considerably earlier than on the Garlock fault and that the two are probably not related. The exact nature of the interaction between the Garlock and Pastoria faults remains controversial. 49 Additional insight would be gained if the age of inception of movement on the Garlock fault were known and if additional dating of the plutonic rocks in the Tehachapi and San Emigdio Mountains were completed. 4. PINON HILL AND LITTLE OAK CANYON FAULTS The northeast-trending Pinon Hill and Little Oak Canyon faults flank the southern exposure of crystalline rocks in the Antelope Valley (Figure 2). Both faults extend northeastward into the range but can not be traced to the Garlock fault, perhaps because of the massive nature of the granodiorite of Gato-Montes in which they occur. Southwestward both faults are buried beneath alluvium. Wiese (1950) cited 3-5 km of left-lateral strike-slip motion, but little or no vertical motion, on the Pinon Hill fault. For the Little Oak Canyon fault, Wiese suggested that both lateral and vertical motions were possible but gave no indication as to the magnitude of these offsets. 5. TYLERHORSE AND COTTONWOOD FAULTS The Tylerhorse and Cottonwood faults extend southeastward through the southern margin of the Tehachapi Mountains into the Antelope Valley where they are concealed beneath alluvium (Figure 2). To the northwest the 50 Tylerhorse fault cuts the granodiorite of Gato-Montes but has not been traced to the Garlock fault. The Cottonwood fault extends northwest to the Little Oak Canyon fault which truncates it. Within the range the faults are clearly exposed, respectively in Tylerhorse and Cottonwood Canyons. Both faults are right-1atera1, strike-slip faults with displacements of 300-500 m (Dibblee, 1963). Eppink (1981), on the basis of gravity and magnetic studies, has suggested that the Cottonwood fault is the northwestern extension of the Willow Springs fault which is exposed along the southside of the Rosamond Hills. 6. TEJON CANYON FAULT The northwest striking Tejon Canyon fault was orignally shown on a map by Lawson (1906) but not discussed in the text. Hoots (1930) later named and showed the Tejon Canyon fault as extending beyond the mouth of Tejon Canyon through the Tejon Hills to the White Wolf fault. Within the Tejon Hills, the fault was suggested to form the contact between the Tertiary clastic and volcanic rocks and crystalline basement. Buwalda (1954) noted such a relationship where the Santa Margarita Formation abutts the granitic basement in a possible fault contact. E x c e p t p e r h a p s i n t h e T e j o n H i l l s , t h e f a u l t is n o t e x p o s e d b u t r a t h e r i s i n f e r r e d o n t h e b a s i s o f t h e s t e e p , 51 west-facing mountain front in Tejon Canyon. If it exists, the Tejon Canyon fault acts as a major lithologic boundary. Northeast of the fault would lie the tonalite of Bear Valley Springs whereas gneisses and granulite occur to the southwest. Because this lithologic boundary extends to the Garlock fault, it indicates that the Tejon Canyon fault must also extend to the Garlock fault. Based on the types of rocks exposed, the sense of movement on the fault would be up on the southwest. C. THE VALLEY SYSTEM Within the Tehachapi Mountains four large intermontane valleys occur, include Tehachapi, Brite, Cummings, and Bear Valleys (Figures 1 and 2). They form a low, planar surface within an otherwise rugged mountain. Each valley is floored by alluvium and is bounded on one or more sides by an abrupt topographic scarp. A controversy exists whether these valleys are dominately erosional or tectonic in origin. It appears that these valleys are controlled by both tectonic and erosional processes. Lawson (1906) indicated the south sides of Tehachapi, Brite and Cummings Valleys were formed by faults. He also suggested that faults occurred along the western margin of Tehachapi Valley and the northeastern margins of Bear, Cummings and Brite Valleys. However, Buwalda (1954) argued 52 that the valleys are predominantly erosional features although he did show faults along several of the valley margins• Dibblee and Warne (1970) mapped a series of northwest striking faults bounding the northeast margins of Bear, Cummings and Brite Valleys. Dibblee and Louke (1970) mapped northwest striking faults along the north side of Tehachapi Valley. Though these faults are vertical and have several hundred meters of displacement, they do not control the location of the northern margin of the valley. T w o n o r t h w e s t - s t r i k i n g n o r m a l f a u l t s o c c u r o n t h e n o r t h e a s t a n d s o u t h w e s t f l a n k s of B e a r M o u n t a i n f o r m i n g t h e B e a r M o u n t a i n h o r s t ( B u w a l d a , 1954; D i b b l e e a n d W a r n e , 1970). T h e f a u l t o n t h e s o u t h e a s t s i d e o f B e a r M o u n t a i n i s t h e s a m e f a u l t w h i c h f o r m s t h e n o r t h e a s t e r n m a r g i n s o f U p p e r B e a r , C u m m i n g s , a n d B r i t e V a l l e y s . N o f a u l t s h a v e b e e n m a p p e d a l o n g o t h e r l i n e a r m a r g i n s o f t h e v a l l e y s . 53 MAGNETICS A. DATA COLLECTION AND REDUCTION Complete high-resolution aeromagnetic data covering the Tehachapi Mountains is lacking. Existing high- resolution data comes from surveys over adjacent regions (U. S. Geological Survey, 19 70 ; Hanna e t al. , 1 972 ; Blake et al., 1977). The range, however, is completely covered by a 1ow—resolution aeromagnetic survey conducted as part of the National Uranium Resources Evaluation (N.U.R.E.) Program under the Department of Energy (Department of Energy, 1980 a,b; 1983 a,b). Aeromagnetic data was collected over both the Los Angeles and Bakersfield 1:250,000 map sheets along north-south flight lines spaced 20 km apart and east-west flight lines spaced 5 km apart. The Department of Energy ( 1980 a,b) data were collected using a total field airborne magnetometer flown at an altitude _<J3 0 0 m. Corrections for diurnal variation were applied and the reference geomagnetic field removed. The smoothed data were contoured to produce total field magnetic anomaly maps for the Bakersfield and Los Angeles sheets (Department of Energy, 1983 a,b). Because the two map sheets were contoured separately, different zero levels were assumed and contours at the map edges did not match. To alleviate these problems, the contours were modified and 54 a d j u s t e d b y h a n d t o p r o d u c e a s i n g l e a e r o m a g n e t i c c o n t o u r m a p f o r t h e T e h a c h a p i M o u n t a i n s a n d a d j a c e n t a r e a s ( F i g u r e 3) . Several short surface magnetic profiles were run to investigate the nature of a few geologic contacts (Figures 4 and 5). Most of the profiles were made across the margins of Bear and Cummings Valleys to determining whether the valleys were fault bounded. The profiles extended from bedrock across the contact with the alluvium and into the valley. Total magnetic field measurements were made using a Geometries Model G—816 Portable Proton Magnetometer. Surface profiles were made along dirt roads or across country to minimize the effects of cultural features (pipes, powerlines, pavement, etc.) which produce noise. The only correction applied to the observed data was for short—period ambient field variations. These corrections were determined by continuously recording the total magnetic field in Bear Valley using a Geometries Model G- 801 Magnetometer. Continuous data were recorded on chart paper and corrections for each profile station were made to the nearest minute. 55 B. RESULTS 1. GENERAL COMMENTS The area of bedrock outcrop in the Tehachapi Mountains is characterized by a relatively flat or smoothly varying magnetic field (Figure 3). Only a few significant positive and negative anomalies occur within the range. Generally, the contours within the range are controlled by anomalies that lie outside rather than within the range. On the north side of the range, between Grapevine and Tejon Canyons (near C, Figure 3) isogams trend northeast, parallel to the bedrock margin. At Tejon Canyon the contours turn southwest parallel to the mountain front. Similarly, in the Mojave Desert contours parallel the northeast trend of the range as far as the head of Tejon Canyon. Northeast of the mouth and head of Tejon Canyon, respectively in the San Joaquin and Antelope Valleys, the contours trend obliquely across the northeast strike of the range. Anomalies within the Tehachapi Mountains resemble those of the Sierra Nevada and the Salinian Block: small, circular, 1ow-amplitude highs and lows (U. S. Geological Survey, 1969 ; Hanna, 1970 , Blake et a 1. , 1977 ). This type of anomaly pattern contrasts with the linear northwest- trending pattern observed over the much of California 56 (Zeitz, 1982). Magnetic anomalies over California reflect the general northwest structural grain. The Coast Ranges, Peninsular Ranges, San Joaquin Valley and Mojave Desert are dominated by northwest—trending anomalies. The San Joaquin Valley displays particularly strong northwest-trending parallel highs. These highs result from outcrops of serpentine in the Coast Ranges and along the margins of the San Joaquin Valley and gabbroic and mafic rocks beneath the San Joaquin Valley (Cady, 1975). Analysis of lineaments observable in the magnetic field over the Tehachapi Mountains suggests that the isogam trends and the shape of the anomalies are not entirely random. Although all azimuths of magnetic lineaments were observed, there was a slightly higher frequency trending east-northeast (N 7 0° E) and west—northwest (N 60° W). This is similar to the highest azimuthal frequencies of topographic lineaments observable in a LANDSAT picture of the Tehachapi Mountains. Topographic lineaments have the highest frequencies at N 70°W, N, and N 60°E. The Garlock fault trends N 50-60°E whereas the San Andreas fault trends N 70°W in the Tehachapi Mountain area, suggesting that both faults play a role in the development of the topographic lineaments. The similar trends of the magnetic and topographic lineaments and the two major faults, suggests that the magnetic anomalies are influenced by structure within the range. Theoretically, total magnetic field anomalies are paired having a positive and negative component. The axis joining the maximum and minimum points in the anomaly pair will lie along the azimuth of the magnetic field vector. In the Tehachapi Mountains, a magnetic high should have an complementary magnetic low lying to the northeast, having an amplitude of 10-20% of the maximum amplitude. The principal is reversible with magnetic lows having induced highs. Additionally, the shape of the body will affect the amplitude of the associated anomaly. Gently sloping contacts will produce an anomaly that is broader and lower in amplitude than steep contacts. However, the pattern typically observed in both aeromagnetic and ground magnetic surveys is the occurrence of a single positive or negative anomaly. Because the associated anomaly has an amplitude which is only a fraction of the inducing anomaly, it is easily masked by the affects of adjacent magnetic anomalies. The Tehachapi Mountains and adjacent areas display what are interpreted to be isolated anomalies. Although some polarization induced anomalies must occur they are not recognizable and are probably masked by the shape effects of the inducing bodies and interference from adjacent anomali e s. Between Commanche Point and Tehachapi Valley the magnetic field is smooth. West of Tehachapi Valley a broad 58 shallow north-trending low occurs at F (Figure 3). Over Tehachapi Valley and to the east and northeast several local highs and lows dominate the field. The contrast in the pattern of the magnetic field reflects the regional geology. West of Tehachapi Valley the tonalite of Bear Valley Springs is the predominate rock type. Eastward, several granitic plutons, large metasedimentary pendants, Tertiary clastic and volcanic rocks, and extensive alluvial covers occur. A north-trending high having a low amplitude occurs on the western margin of Tehachapi Valley at 0. Northeast of Tehachapi Valley, an east-northeast-trending low and a circular low occur at I and I' and correspond to Tertiary volcanic rocks. The high at H occurs over southeastern Tehachapi Valley and the bedrock ridge which separates the valley from the Mojave Desert. The western Antelope Valley exhibits a southward decreasing field having east- to northeast-trending isogams. This pattern contrasts with the field observed in the northeastern Antelope Valley, near Mojave. There, several positive and negative anomalies (J,K,L,M,N) have 10—15 km wavelengths and residual amplitudes of +100 — 2 00 gammas. Locally, gradients around these anomlies exceed 40 gammas/km. 59 2. SAN JOAQUIN VALLEY Two of the largest positive anomalies observed in the area occur in the San Joaquin Valley (anomalies A and B, Figure 3). Anomaly A has an amplitude of over 300 gammas whereas anomaly B has an amplitude of 100 gammas. The anomalies occur where the sedimentary thicknesses are approximately 3-5 km. Basement rocks have never been penetrated in either area but the basement rocks observed closest to both anomalies are greenschist and amphibolite (Ross, 1985a). Data from drill holes near the edge of the valley (Ross, 1979; May and Hewitt, 1948) indicate that the lithology of the basement rocks is variable in the southern San Joaquin Valley. The two positive anomalies are part of a zone of prominent magnetic highs extending for more than 700 km along the length of the San Joaquin Valley. The preferred explanation for these anomalies is the occurrence of subsurface mafic and ultramafic rocks (Griscom, 1966; Cady, 1975 , Blake et a1. , 1977), consistent with gravity data and drill core samples from other parts of the valley. 3. BEDROCK OF THE TEHACHAPI MOUNTAINS I n t h e s o u t h w e s t e r n T e h a c h a p i M o u n t a i n s , w h e r e t h e m e t a m o r p h i c r o c k s o u t c r o p , t h e m a g n e t i c f i e l d d e c r e a s e s 60 southward across the range. Gradients in this area are 7 — 12 gammas/km. The shape of the contours indicates that the field is higher over this part of the range relative to that farther northeast. Part of the higher level results from the high at B and part from the greater magnetic susceptibi1ty of the rocks. Metamorphic rocks from the region have magnetic susceptibilities of 5 to 20 times that of the granitic plutons (Table 1). The tonalite of Bear Valley Springs is the principal rock type in the northwestern Tehachapi Mountains and is characterized by a smooth field which exhibits only a shallow, north trending low (F, Figure 3). An aeromagnetic line flown across the tonalite (Figure 6, line 1) shows several anomalies unrelated to structure or gross lithology. Individual aeromagnetic lines over this area show short-wavelength (5-10 km), low-amplitude anomalies, indicative of a nearby source. Several ground magnetic profiles run across the tonalite also show significant field varations (Figures 4 and 5). Because these were surface surveys, the observed variations could not be associated with topography. Anomalies observed on the ground have wavelengths of 100— 200 m and amplitudes of 20-40 gammas. Although these profiles crossed the contact between the tonalite and alluvium, much of the variation occurred entirely within t he to nali t e. Aeromagnetic anomalies result from two principal causes; topography and susceptibility changes in the rocks. Many aeromagnetic lines are flown at constant barometric altitude, hence the altitude above the ground varies. Anomalies often result simply from changes in the elevation of the sensor above the ground. High magnetic fields are observed over high topography and vice-versa. Many of the anomalies observed on individual flight lines in the Tehachapi Mountains result from this effect. Very often, however, the anomalies are not related to topography and reflect variations in rock susceptibility, particularly on the ground profiles. Aeromagnetic profiles over the Sierra Nevada show anomalies similar to those observed over the Tehachapi Mountains (Oliver, 1970; 1972; 1977; 1982b). Both airborne and surface profiles show anomalies within single plutons unrelated to topography. Surface profile anomalies have amplitudes of >100 gammas and wavelengths of a few hundred meters, similar to those observed here. Anomalies within a single rock body have been suggested to result from compositional variations, principally the amount of magnetite (Oliver, 1970; 1972; 1977; 1982). Magnetic anomalies observed over the tonalite of Bear Valley Springs in both surface and airborne data reflect a variation in the magnetic susceptibility of the rock. These changes can arise from mineralogic variation or inclusion of foreign rocks. 62 Data from Ross ( 1985a) suggest that the tonalite exhibits large variations in the amount of hornblende and biotite, two important iron-bearing minerals. Local increases in the percentage of these minerals increase the bulk susceptibility of the rock, thereby increasing the intensity of the ambient field. Limited sampling of the tonalite indicates susceptibilities of 0.16 to 0.25 X 10 ^ _ 3 emu cm . Bulk susceptibility variations could also arise from the numerous, centimeter to meter diameter, mafic xenoliths found in the tonalite. The higher mafic content of these xenoliths increases the bulk susceptibility of the tonalite in areas of high xenolith content. Measurements of several mafic inclusions indicate susceptibilities of approximately 0.49 X 10 emu cm , about 2—3 times that of the tonalite. Chemical variations are the probable cause for the small-scale magnetic anomalies observed in the ground data and those anomalies unrelated to altitude in the airborne data. When viewed on a regional scale (Figure 3), however, the smooth field indicates that the pluton is magnetically homogeneous• The high at H is centered over an outcrop of the granodiorites of Claraville, Gato-Montes and Cameron and has an amplitude of about 40 gammas. Though the outcrop pattern of these rocks trends northeast the anomaly trends east-northeast. The positive polarity of the anomaly 63 suggests that the granodiorites are more magnetic than either the tonalite to the west or the plutons to the north. The ridge is predominately granodiorite of Claraville which has a susceptibility several orders of magnitude higher than the other granitic rocks in the area (Table 1). It is presumably the granodiorite of Claraville that is responsible for the anomaly. The low at C (Figure 3) in the southwestern part of the range results from a cultural rather than a geological cause. One east-west flight line crossed directly over the Aqueduct Pumping Station and observed a 500 gamma negative anomaly. Parallel east—west profiles lying 5 km north and south observed no indication of a low at this longitude. Geologic maps of the area (Ross, 1980; Dibblee, 1973 a,b) do not indicate a geologic source for the anomaly. The anomaly's localized nature suggests that it is related to the pump plant. Apparently, because of its amplitude, the smoothing and contouring routines used to produce the map (Department of Energy, 1983b) enlarged the anomaly. A large positive anomaly within the range occurs at P, in the northeast corner of the map area (Figure 3) and has an amplitude of 200 gammas and gradients of 20 gammas/km. The anomaly lies just west of the Sierra Nevada frontal fault and is centered over a bedrock re-entrant. Basement rocks in the area include tonalite of Hoffman Canyon, granodiorite of Claraville, granite of Bishop Ranch and 64 mafic gneiss and amphibolite of Jawbone Canyon (Ross, 1980). The granodiorite of Claraville has susceptibilites / Q of 0.15-12.5 x 10 emu cm . No sample was obtained from the area of the anomaly but if those rocks have susceptibilities on the high end of the observed range, they could be responsible for the anomaly. 4. TERTIARY ROCKS NORTHEAST OF TEHACHAPI VALLEY A significant anomaly pair observed within the Tehachapi Mountains are the negative features at I and I' (Figure 3). This double anomaly occurs over Miocene volcanic and clastic rocks: the Winet, Kinnick and Bopesta Formations. Pyroclastic tuffs dominate the Kinnick Formation and the entire Tertiary section is overlain by younger lavas. The anomaly at I trends east-northeast and covers approximately 20 by 10 km whereas the smaller anomaly at I" is circular, 10 X 10 km. The low at I has an amplitude of —100 gammas, north—south gradients of 20 gammas/km and east-west gradients of 4 gammas/km. Anomaly 1' has an amplitude of 40-50 gammas and gradients of 10 gammas/km. A east-northeast trend for the anomaly is consistent with the outcrop area of the Tertiary rocks (Dibblee and Louke, 1970). The smaller low at 1' occurs over a circular basin of these same rocks centered at Cache Peak. 65 Limited sampling of the volcanic and clastic rocks in Sand Canyon indicates variable magnetic susceptibilities (Table 1). Low susceptibilities (0.1-0.5 X 10”^ emu cm"^) characterize the elastics and high susceptibilities (1.2- / o 2.2 X 10 emu cm ) are typical of the basalts which form a thin cap on top of the section. Underlying the volcanic and clastic rocks is the granodiorite of Claraville which has a large susceptibility range (Table 1). The negative anomaly could be caused soley by the thick section of relatively non-magnetic volcanic and clastic rocks. A i susceptibility contrast of 4-5 X 10 emu cm between the basement and a 2 km thick section of volcanic and clastic rocks would be sufficent to produce the observed negative anomaly. The amplitude and position of the lows at I and I' is such that they are not polarization lows associated with the high at H (Figure 3). Vacquier e t al. (1951) showed a polarization low induced by a magnetic high would occur to the north-northeast and have an amplitude of 0.1 - 0.3 times the inducing high. The low at I lies due north of the high at H and has a residual amplitude of -100 gammas compared to the +20-40 gammas amplitude of the high. This is inconsistent with it being a polarization low. 66 5. ANTELOPE VALLEY The westernmost Antelope Valley is characterized by a southward decreasing field (Figure 3). Bedrock does not outcrop in the region as it is buried beneath a thick section of sediments (Mabey, 1960). Magnetic anomalies are not associated with these basins suggesting that the sediments do not have a large magnetic contrast with the bedrock exposed in the surrounding mountains. At the southern end of the map, the low at G overlies the San Andreas fault and Tertiary clastic and volcanic rocks which crop out north of the fault. This low could result from reversly magnetized volcanics, but the age and polarity of the volcanic rock have not been studied. A large positive anomaly occurs farther south, outside the map area, and Hanna et al. (1972) have interpreted the low at G to be a polarization effect of this high. A completely different magnetic field characterizes the eastern Antelope Valley near Mojave (Figure 3) where several 5-10 km wide, high—amp1itude anomalies (J,K,L,M,N,) occur. These anomalies are associated with outcrops of plutonic and volcanic rocks. Anomaly N has an amplitude of 160 gammas and lies north of the Antelope Buttes, an outcrop of quartz raonzonite. The anomaly may reflect the subsurface distribution of the quartz monzonite or it may be caused by completely different rocks at depth. The 67 positive anomalies at M and L correspond to exposures of quartz monzonite, respectively over the Rosamond Hills and an unnamed ridge to the north. Anomaly M has an amplitude of about 200 gammas and anomaly L has an amplitude of 140 gamma s• The northeast-trending low at K occurs over an exposure of the Tertiary Gem Hill Formation (Dibblee, 1963). The Gem Hill Formation consists of rhyolite, quartz latite, and dacite pyroclastics and intrusions which are exposed in Soledad Mountain, Middle Buttes and Willow Springs Mountain. Anomaly K has an amplitude of 80-100 gammas and covers an area of 8 x 18 km. Rhyolites are generally the least magnetic of the volcanic rocks (Table 1) having susceptibilities of 0.2-30 __ 4 _ 3 X 10 emu cm . Dacite, which forms intrusive plugs in these areas, is considerably more magnetic and presumably is responsible for the anomaly. The negative polarity suggests the rocks are reversely magnetized but they have not been studied. The pattern of magnetic anomalies in the Antelope Valley indicates that highs are associated with plutonic rocks (i.e., quartz monzonite) and negative anomalies occur over areas of volcanic rocks. 68 6. PENDANTS The closed high at 0 (Figure 3) in the central Tehachapi Mountains occurs over the Brite Valley metasedimentary pendant. Two aeromagnetic lines crossed the pendant (Department of Energy, 1983a) and are illustrated in Figure 6. The southern flight line (Profile 1) displays a 5 km wide positive anomaly having an amplitude of 30-40 gammas. Superimposed on the broader anomaly are smaller amplitude (10 gammas), shorter wavelength (500 m) variations. The relative low at A (Profile 1) occurs over Brite Valley and reflects the alluvium and subsurface t onali t e. The broader anomaly is asymmetric having a higher gradient on the west side (40 gammas/km) than on the east side (10 gammas/km). Such asymmetry is consistent with the map of Dibblee and Warne (1970) which shows a northeast to east-northeast dip of 50°-60° for the pendant. Profile 2 (Figure 6) observed poorly define anomalies at A and B. These anomalies are more variable and broader than to the anomaly to the south (Profile 1) but show a similar a symme try. Surface magnetic profiles were run across the margins of the pendant in several locations (Figure 5). Although the data is noisy, lines G, H and I confirm the higher field levels over the pendant relative to the surrounding tonalite of Bear Valley Springs. 69 In Tehachapi Valley, a second series of magnetic highs at B on Profile 1 and at C and D in Profile 2 (Figure 6) occur over extensions of metasedimentary pendants which crop out on the margins of the valley. The anomalies have asymmetric amplitudes of 20 gammas and are about 2 km wide. Ground and airborne magnetic data indicate the Brite Valley and Tehachapi pendants exhibit higher magnetic fields than the surrounding tonalite of Bear Valley Springs. Samples from the Tehachapi, La Liebre and Bronco Canyon pendants indicate that the marbles have very low susceptibilities. Values for the marble range from -0.005 X / O / Q 10"~ emu cm” (diamagnetic) to 0.07 X 10 emu cm (Table 1). Hornfels samples in the La Liebre pendant have susceptibilities of 0.08-0.09 X 10”^ emu cm"^. The field within the pendant is highly variable suggesting that the distribution of the different rock types (marble, schist, hornfels, etc.) control the anomaly shape. The La Liebre pendant within the granite of Tejon Lookout is composed of marble and minor hornfels and schist (Crowell, 1952). The pendant was traversed by an aeromagnetic line at its widest exposure and exhibited a complex anomaly (Figure 7) that can be divided into an eastern and western half based on its characteristics. Magnetic variations over the eastern half have amplitudes of approximately 10 gammas and wavelenths of 3 km. Over the western half, the variations have amplitudes of 50-200 70 gammas and wavelengths of 200 m. Short-wavelength, high- amplitude anomalies suggest a shallow or exposed source. La Liebre marbles are non-magnetic or diamagnetic, although hornfels are slightly more magnetic (Table 1). Mabey (1961) observed that hornfels in the Argus Range exhibited large-amplitude positive magnetic anomalies. The aeromagnetic line over the La Liebre pendant crossed only marble but hornfels crop out immediately to the north and may be more widespread throughout the western part of the pendant at a shallow depth. It therefore seems likely that the anomalies observed over the western part of the La Liebre pendant result from the presence of the hornfels. The Bronco Canyon pendant is composed of about two- thirds marble and one—third schist. Aeromagnetic profiles revealed no anomaly relative to the surrounding granite of Tejon Lookout. The absence of an anomaly results both from the low susceptibilities of the marble and the granite (Table 1) and the lack of a susceptibility contrast. The only other pendant south of the Garlock fault crossed by an aeromagnetic line was the Bean Canyon pendant. This pendant is approximately 1 km wide and is composed mostly of schist and some associated basic volcanic rocks. No anomaly was detected at an altitude of 300-600 m across the southern tip of the pendant. In light of the mafic volcanic rocks, the absence of an anomaly is surprising. However, the small source size and the relatively high altitude of the flight line may have prevented detection of an anomaly. With the exception of the Brite Valley and Tehachapi pendants, metasedimentary pendants in the Tehachapi Mountains do not display well-defined anomalies. Locally, both positive and negative anomalies occur but they are not consistent. Hornfels appear to induce positive anomalies; quartzite and schist positive or negative anomalies. Marbles do not exhibit any anomalies. The absence of significant anomalies indicates that little or no susceptibility contrast exists between the plutonic and metasedimentary rocks. Magnetic profiles across pendants of metasedimentary and metavolcanic rock the Sierra Nevada show both positive and negative anomalies. An aeromagnetic survey over the Sierra Nevada between 37° and 37.25°N (U. S. Geological Survey, 1969) showed pendants of Jurassic-Triassic metavolcanic rocks exhibiting positive anomalies and pre- Cretaceous metasedimentary rocks exhibiting positive, negative or no anomalies. Surveys in other parts of the Sierra Nevada observed similar patterns (Oliver, 1970, 1972, 1982). Generally, magnetic susceptibilities of the metavolcanic pendants are one to two orders of magnitude higher than those of metasedimentary pendants (Table 1). Susceptibilities of the granitic rocks in the Tehachapi 72 Mountains are quite low, typcially less than 0.2 X 10 ^ emu _ 3 cm As a result, in some cases the pendants produce positive anomalies and in others negative anomalies. The absence of anomalies over the metasedimentary pendants of the Tehachapi Mountains is consistent with observations elsewhere in the Sierra Nevada. 7. THE INTERMONTANE VALLEYS Several surface magnetic profiles were run across the margins of Bear Valley and Cummings Valley in an attempt to determine if the valleys were fault bounded. Figures 4 and 5 show the profile locations as well as portions of two aeromagnetic lines which also cross the valley margins. The magnetic profiles were inconclusive regarding the presence of faults. The contact between the tonalite and the alluvium within the valley does not exhibit a consistent magnetic signature. Anomalies observed on the profiles had short wavelengths whi ch were not associated with the valley margins. The absence of a magnetic signature at the alluvium-tonalite contact suggests that the remnance of the tonalite is very low, consistent with measurements which indicate that the remnance is on the order of 5 X 10 ^ emu. Thus, when the rock was disaggregated and redeposited as alluvium, it would have a net magnetization similar to that of the intact tonalite, i.e. one dominated largely by an induced component. 73 Two aeromagnetic lines (Profiles 1 and 2, Figure 5) cross the valley margins. Profile 1 exhibits two small anomalies (A and B). Anomaly A occurs over a narrow bedrock ridge that extends northwest into the alluvium and separates Middle and Lower Bear Valleys. A second anomaly at B is observed over the southwest edge of Upper Bear Valley. These anomalies are similar to the patterns observed in the ground profiles A, B and D (Figure 5) and may reflect some structural affect. However, in light of the variations observed on the ground and in the western part of aeromagnetic profile 1, the more likely explanation is that these anomalies reflect variations in the rock magnetization rather than structure. A second aeromagnetic line to the south, in western Cummings Valley (Profile 2), shows no signature over the contact between alluvium and bedrock. C. SUMMARY In summary, the magnetic field over the Tehachapi Mountains is dominated by relatively few anomalies and can generally be described as a smoothly varying field. Over the southwest part of the range, the field decreases into the Antelope Valley from a high in the San Joaquin Valley. The tonalite of Bear Valley Springs, the largest pluton, is characterized by smal1—amplitude magnetic variations 74 resulting from local changes in magnetic susceptibility. Tertiary volcanic and clastic rocks north of Tehachapi Valley exhibit a pronounced negative anomaly resulting from the thick section of these relatively non-magnetic rocks over highly magnetic basement, the granodiorite of Claraville. Metasedimentary pendants do not display consistent anomalies. Pendants south of the Garlock fault generally do not exhibit anomalies. Magnetic anomalies of pendants north of the fault are typically positive but irregular. The large positive anomaly in the northeast corner of the map probably results from the local increase in the susceptibility of the granodiorite of Claraville. Neither of the major faults, the Garlock or White Wolf, are characterized by a pronounced magnetic anomaly. Magnetic data suggest that in general, there is little variation in the susceptibilites of different rock types or a large contrast with the alluvium that fills the valleys. This results from the generally low reranances and susceptibilities• Several heat flow measurements have been made in the Tehachapi Mountains (Henyey and Wasserburg, 1971; Sass e t a1. , 1971) which indicate heat flows of 1.29-2.21 H.F.U. These values are considerably higher than in the Sierra Nevada where heat flow is generally <1 H.F.U. , but are similar to that for the Mojave Desert (Sass et a 1. , 1971; 75 Lachenbruch and Sass, 1977). Theoretical modeling of the temperature profile through the crust (Lachenbruch and Sass, 19 77 ) has not been carried out specifically for the Tehachapi Mountains. However, the depth to the Curie Point in the Mojave Desert-Tehachapi Mountains region probably lies at 18-28 km below the surface (J. Sass, personal communication, 1984). A Curie Point (500—600°C) at 18-28 km indicates that the magnetic field anomalies observed in the Tehachapi Mountains are all generated within the upper crust. A shallow source is also consistent with the generally short wavelengths and large gradients associated with the anomalies• 76 GRAVITY A. DATA COLLECTION AND REDUCTION Gravity data (Figure 8) were collected in the Tehachapi Mountains to examine details of the local and regional gravity field. As the purpose was to investigate crustal structure in the Tehachapi Mountains, measurements were concentrated within the range where existing data were limited. Extensive data already existed for the San Joaquin and Antelope Valleys and this was incorporated into the data set used in the analysis. In addition to that collected on a regional scale, data were collected along profiles of closely spaced stations to allow detailed crustal modeling. The existing data base of more than 1700 stations were added to the collected data for analyses. Using a Worden Gravity Meter, Master Model III (No. 758), 1057 gravity stations were measured. Stations used in the study are shown in Figure 8. A complete listing the gravity data collected during the study is listed in Appendix I. Six profiles were measured: 1) Southern California Edison (SCE) Pardee-Pastoria transmission line #3; 2) California Water Resources Aqueduct Access Road; 3) SCE Antelope-Magunden transmission line #1; 4) Bear Mountain Boulevard (California Highway 223); 5) Tehachapi- 77 Bakersfield Highway (California Highway 58); and 6) Tehachapi-Willow Springs Road. Station spacing along paved roads was 400 m (0.25 mi) and 300-400 m along the transmission lines. The locations of these profiles (Figure 1) were selected based on the availability of accurate elevation data. Station elevations were acquired through various means. Details of the source and accuracy of the elevation data can be found in Appendix II. All gravity measurements were tied, either directly or indirectly, to one of 5 stations at which absolute gravity had been determined. These ties allowed an absolute gravity value to be assigned to each station. Absolute gravity stations used include: ARVIN, FTTJN (Ft. Tejon), FRZPK (Frazier Park), and TCHPI (Tehachapi Airport), from Hanna and Sikora (1974), and the Mojave Triangulation Station (U.S. Coast & Geodetic Survey Mojave 1958), from Chapman ( 1966). Instrument drift was established by occupying a base station every 2 to 3 hours. Lunar and solar tide variations, in addition to the instrument drift, are accounted for by this procedure. Topographic corrections were manually computed out to zone 0 (120 km) using methods outlined by Hammer (1939). The topographic corrections for zones A (0-2 m) and B (2- 16.6 m) were estimated in the field at each station. When possible, stations were sited such that the Zone A 78 correction was zero. However, because of the rugged topography and limited number of candidate sites this was not always possible. Zones C to K (16.6 m - 9.9 km) were estimated from the 1:62,000 maps sheets and zones L through 0 (9.9-120 km) from 1:250,000 map sheets. Reduction of observed gravity to a complete Bouguer gravity anomaly was computed using sea level as the datum. _ 3 A crustal density of 2.67 g cm was used in the Bouguer and topographic corrections as originally proposed by Swick (1942) and subsequently generally followed. Relevant equations for reduction include: Theoretical gravity (Gt) G = 978049 (1 + 5.2884 X 10 3 sin2 L - 5.9 X 10"6 sin2 2L) (1) Curvature correction (C) C= 1.27 X 10"15 H3 3.282 X 10~8 H2 + 4.462 X 10 -4 H (2) Free Air Anomaly (FAA) FAA = H (9.41159 X 10 2 - 1.37789 X 10“4 sin2 L - 6.7 X 109 H2) + G - G. o t (3) 79 Complete Bouguer Gravity Anomaly (BGA) BGA = FAA + TC - C - 3.410658 X 10 2 H (4). In the above equations, L is the station latitude, H the station elevation above the datum in feet, TC the terrain correction in mgal and Gq the absolute observed gravity. B. GRIDDING AND FILTERING One objective of this study was to determine what, if any, correlations exist between the gravity field and the geology and structure. As most of the individual geologic features, plutons, pendants and basins, are relatively small, their presence could be masked by large gravity gradients. In order to isolate small anomalies the gravity data were filtered. Filtering programs based on Reed (1980) and developed by Fogarty (1985) at the University of Southern California for use on a VAX 750 were used in the study. Fogarty's revisions are subject to fewer errors and are therefore more accurate than the original work by Reed. In addition, the revisions take advantage of the capabilities of the current computing facilities (see Appendix II for additional details). Upward continuation, band-pass filtering, and vertical derivatives were used. qq Several different band passes were used in an attempt to produce the best representation of the small-scale features, A grid spacing of 4 km limited the smallest observable anomaly to 8 km. Generally, filters which passed wavelengths of 8 to <16 km were not successful at isolating anomalies. Though many rock bodies were smaller than 16 km, the spacing of the original data often precluded their resolution. The best anomaly separation was obtained by passing wavelengths between 8 and 16-22 km. These filtered versions indicated several additional anomalies both as closed contours and deflections of the contours. Upward continuation depicts the gravity field that would be measured at an arbitrary altitude above the surface of the earth and has the effect of suppressing shallow near-surface anomalies while preserving the larger, presumably deeper, anaomlies. Continuation is also useful in noise suppression. The results of upward continuation are similar to those from low-frequency band—pass filtering. Downward continuation depicts the gravity field as it would be observed at a level below the surface and has the opposite effect of upward continuation. High- frequency anomalies are enhanced at the expense of low- frequency anomalies. The results are similar to a high- frequency band—pass filter. Derivatives up the Nth level in the horizontal (X and Y) or vertical (Z) directions can be calculated for gravity 81 data. However, only the 1st and 2nd derivatives of the gravity field, respectively the 2nd and 3rd of the potential field, in the Z (vertical) direction are used routinely. The 1st derivative in the horizontal direction gives the gravity gradient in that direction. As derivatives in the horizontal direction could be calculated only in the east-west or north-south direction, parallel to the grid axes, they were not used. Horizontal gradients were measured directly from the contour maps. Vertical derivatives have the ability, in some cases, to emphasize small-scale anomalies in the gravity field. The first derivative (the gradient) and the second derivative (the curvature) tend to accentuate small scale sources. Near-surface sources produce small anomalies which have large changes in gradient and small radii of curvature. Hence, these aspects are enhanced in the derivative fields. The 1ong-wavelength features, those with small gradients and large radii of curvature, are s uppr e s s ed. C. MODELING Modeling programs used in this study were developed by Fogarty (1985) based on work by Cady (1980) and are similar to the classic modeling programs of Talwani and Ewing (1960). The program calculates the gravity over a group of 82 polygonal bodies. The extent of the bodies normal to the profile can be set at infinity or an arbitrary distance. In general there is little difference between the calculated gravity for a body of infinite extent or one having an extent of a few tens of kilometers. However, the ability to control the dimension of the body normal to the profile allows the computation of the gravity over a body of finite size, such as an individual pluton or a valley. Gravity values are calculated at points along a profile. In the _ 3 models calculated here, density contrasts with 2.67 g cm were used. D. RESULTS 1. GENERAL COMMENTS The focus of this study has been to significantly add to the exisiting gravity data base and attempt to determine aspects of the crustal structure from that data. Analysis of crustal structure was undertaken at two scales; a regional scale to investigate the crustal structure of the range as a whole, and a local scale to study aspects of individual plutons, pendants, and valleys. Results are presented in two sections, a description of the individual anomalies then a discussion of the regional aspects of the crustal modeling. 83 Reconnaissance data for the Tehachapi Mountains indicates that a gravity high dominates the range (Oliver and Mabey, 1963 ; Hanna e t al. , 1974 a,b; Oliver, 1980). Published gravity data in the Tehachapi Mountains and southern Sierra Nevada are relatively sparse; approximately 2 1 station per 5 km • Locally, along a few major roads, more closely spaced data exist. Existing gravity data in the Antelope and San Joaquin Valleys are quite dense and have 2 station spacings of about 1 station per km . The gravity high over the Tehachapi Mountains, illustrated in Figure 9, results both from the high density of the rocks exposed in the range and from the density contrast with the low-density sediments that flank the range. Gravity in the southern San Joaquin Valley reaches <-100 mgal, over the Kern Lake Bed, and <-120 mgal in the western Antelope Valley. In the southern San Joaquin Valley the low gravity results from >9 km of post-Miocene low- density sediments. Low gravity in the Antelope Valley results from low-density alluvium which fills several basins. Mabey (1960) estimated that 1000-3000 m of alluvium occurs in the Antelope Valley basins. The Tehachapi Mountains act as a transition zone between the high gravity of the Coast-Transverse Ranges and the low gravity of the Sierra Nevada batholith. When viewed in a regional context (Figure 10), the gravity of the Tehachapi Mountains is similar to that of the western 84 Sierra Nevada and central Penisular Ranges, i.e. gravity values of -50 to -100 mgal. Bouguer gravity over the area is strongly negative, typical of much of the western United States. Previously published gravity data (Hanna et al. , 1974 a,b) for the Tehachapi Mountains showed essentially no correlation between gravity and geology. Contours crossed contacts between various rock bodies with little or no deflection. This lack of correlation results from the large gravity gradients which characterize the range and overwhelm the small-scale anomalies that might be associated with specific rock bodies or structures. Figure 9 illustrates the complete Bouguer gravity map for the Tehachapi Mountains and adjacent areas. This map was produced from a 16 X 16 matrix using a 4 km grid spacing and a contour interval of 2 mgal. Gravity over the Tehachapi Mountains is dominated by a broad high at A centered over the metamorphic terrane of the southwestern part of the range and flanking lows in the Antelope and San Joaquin Valleys. Because these anomalies are so closely spaced, large gradients dominate the range. Isogals closely parallel the bedrock outcrop pattern. Within the San Joaquin Valley, contours parallel the White Wolf fault southwest to Commanche Point, turn southward across the Tejon Hills then again southwest along the range from Tejon to Grapevine Canyons. In the Antelope Valley, 85 isogals parallel the range front from the San Andreas fault to Mo j ave. Maximum gravity observed in the study area was -53 mgal over Grapevine Canyon, whereas the lowest observed was -121 mgal in the Antelope Valley. These values indicate gravity relief of 70 mgal between the range and the Antelope Valley and 50 mgal with the San Joaquin Valley. Gravity relief along the axis of the range, between the high at A and the low at L, is about 60 mgal. Gradients are highly directional (Figure 9) with northwest gradients being larger than those to the northeast. Along the flanks of the range, gradients into the Antelope Valley decrease from 4 mgal/km in the southwest to <2 mgal/km in the northeast. Gradients into the San Joaquin Valley are typically 3 mgal/km. Along the axis of the range the gravity gradient is <1 mgal/km. The northeast trending high (A) is centered over the metamorphic rocks of the southwestern Tehachapi Mountains and extends westward into the San Emigdio Mountains. Northeastward it divides into two branches B and C (Figure 9). The eastern branch (C) has 4-6 mgal of relief and follows the metamorphic terrane which occurs southwest of Tejon Canyon and north of the Garlock fault. The north anomaly at B, centered over the Tejon Hills, has several closed contours and displays about 6 mgal of relief. 86 The major east-west trending low at E occurs in the western Antelope Valley. Northwest of the range, the major low of the San Joaquin Valley is indicated by the steep gradient west of B (Figure 9). Several smaller anomalies are also observed. Small highs occur at I (-69 mgal) and at J (-85 mgal). The elongate high at I measures approximately 5 X 8 km and has an amplitude of approximately 7 mgal. It is associated with bedrock south of the Edison fault. Anomaly J has 2 mgal of closure and occurs over the Tehachapi metasedimentary pendant. The 2 mgal low at H lies within the tonalite of Bear Valley Springs and straddles the White Wolf fault. The closed low at L and the distorted contours to the south at K are associated with Tertiary clastic and volcanic rocks northeast of Tehachapi Valley. Several subsidiary lows occur in the Antelope Valley at F and G and have gravity of —117 and -116 mgal, respectively. Local deflections of the isogals in several areas indicate incompletely resolved, positive and negative anomalies (Figure 9 ) . The principal gravity lows of the Antelope and San Joaquin Valleys juxtaposed against the Tehachapi Mountain high produce large gravity gradients which dominate the region (Figure 9). As a result, only the most pronounced anomalies are observable on the contour map. Smaller anomalies are either completely masked or indicated only by a deflection of the isogals. In order to remove regional 87 effects and resolve small-scale features, the gravity data were band-pass filtered (see Gridding and Filetering section and Appendix II). This method proved successful in isolating local structure in the gravity field which was not observable in the original contour data. Significant correlations of local anomalies with specific rock bodies and structures are possible as a result of filtering. 2. SPECIFIC ANOMALIES a. METAMORPHIC TERRANE The principal gravity feature of the Tehachapi Mountains is the positive anomaly over the metamorphic terrane (Figure 9). The anomaly consists of two closed contour features at A and B and an extension defined by a deflection of the isogals at C. The high at A results from the metamorphic rocks which characterize the western Tehachapi and San Emigdio Mountains. These rocks include hornblende-ri ch and felsic gneisses, as well as quartzites and schists (Ross, 1983, 1985a; Sharry, 1981). Drill hole samples indicate that similar metamorphic rocks underlie the sediments of the southern San Joaquin Valley (Ross, 1979; May and Hewitt, 1948). The metamorphic rocks have — 3 densities of 2.60-3.06 g cm (Table 2), considerably higher than the adjacent valley sediments and plutons. 88 Using a band-pass filter of 8-18.3 km, a contour map (Figure 11) was produced which better defines the northeast trending highs over the metamorphic terrane and the high over the Tejon Hills. A smaller area of the southwestern Tehachapi Mountains was gridded and contoured to better resolve the two positive anomalies and the gravity ridge (Figure 12). Filtering of that data (Figure 13), using an 8-16 km band pass, clearly resolves the main northeast trending high (A) and the second positive anomaly over the Tejon Hills (B). The northeast trending gravity high (denoted by the dashed line in Figures 11 and 13) has 2-4 mgal of relief and follows the metamorphic rocks into the upper reaches of Tejon Canyon. In that area the metamorphic rocks pinch out between the Pelona schist to the south and the transitional rocks in Tejon Canyon to the north. Gravity over the metamorphic terrane north of the Garlock and Pastoria faults is 18-20 mgal higher than over the granitic plutons south of the faults or the tonalite of Bear Valley Springs to the northeast. The high at A (Figure 12) is asymmetric having a steep southward gradient and a shallow saddle separating it from the high at B. The steep southward gradient (2-3 mgal/km) results from the density contrast between the metamorphic rocks and granitic plutons across the Garlock and Pastoria faults. 89 The closed-contour high at B (Figures 11 and 13) is centered over the Tej on Hills and has a residual anomaly of 8 mgal extending over an area of 18 X 25 km. A magnetic high also occurs over the same area (B in Figure 3). The correlation of gravity and magnetic anomalies in the western Sierra Nevada foothills and San Joaquin Valley has been interpreted to result from ultramafic bodies at depth (Cady, 1975; Blake et al. , 1977). Dense rock beneath the anomaly is also suggested by the low density of the clastic rocks exposed in the Tejon Hills. Only with appreciable quantities of high density material at depth can a positive anomaly occur over a surface outcrop of low-density ma terial. b. GRANITIC ROCKS SOUTH OF THE GARLOCK AND PASTORIA FAULTS Extending from the San Andreas fault to Tejon Canyon, the Garlock and Pastoria faults juxtapose high-density metamorphic rocks to the north against low-density granitic plutons to the south. Westward from the point of intersection of the Pastoria fault and the north and south branches of the Garlock fault, the Pastoria fault acts as the lithologic boundary, whereas the westernmost Garlock fault continues toward the San Andreas fault entirely within granitic rocks. The granitics have densities of _ q 2.61-2.67 g cm which are lower than the metamorphic rocks 90 to the north. Because of the differences in density, a _ 3 density contrast of up to 0.45 g cm occurs across the f ault s. South of the Pastoria fault, the granodiorite of Lebec is marked by a 6-8 mgal low at D (Figures 11 and 13). The granodiorite is surrounded by regions of higher gravity resulting from Pre-Cambrian gneiss and schist of Frazier Mountain to the south and the metamorphic rocks to the north. Gravity increases eastward onto a saddle over additional outcrops of granodiorite of Lebec and granite of Tejon Lookout. The granitic rocks south of the Garlock and Pastoria faults are characterized by a step in the gravity field (F in Figure 13) both sides of which are marked by higher gravity gradients. Over the granitic plutons gradients are only 0.4—0.7 mgal/km compared to 3—4 mgal/km on either side. Northeastward the outcrop area of the plutons narrows and this is reflected by a disappearance of the gravity step. Sou thwe s twar d, the step widens as does the outcrop area of the granitic plutons. The northern edge of the step, marked by a large gradient, follows the Pastoria fault rather than the Garlock fault at its westernmost end. The step is the result of a crustal section of intermediate density juxtaposed between high-density metamorphic rocks and low-density sediments. 91 c. PENDANTS Pendants of metasedimentary and metavolcanic rock occur within the Tehachapi Mountains, north and south of the Garlock fault (Figure 1). These pendants exhibit gravity signatures reflecting their lithology and that of the surrounding rocks. The density of the pendants is relatively uniform and it is the density contrast that determines the polarity and magnitude of the anomaly. Neither the La Liebre pendant, the westernmost and largest of the pendants, nor the smaller Bronco Canyon pendant display a gravity anomaly (Figures 10-13). The lack of an anomaly over either pendant results from the lack of a density contrast between the limestone and the enclosing plu t o ns. The Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon pendants appear to have minor positive anomalies (F, G, and H in Figure 11). The anomalies over these pendants have amplitudes of 1-2 mgal and are indicated by a deflection of the isogals. These pendants occur in the same group of plutons (granodiorites of Gato- Montes and Cameron) as do the La Liebre and Bronco Canyon pendants. Hence, the presence of a positive gravity anomaly indicates that the bulk densities of the northeastern group of pendants must be higher than those to the southwest. 92 Models of the the La Liebre and Bronco Canyon pendants indicate that the density of the pendants could be no more _ 3 than 2.70 g cm as a higher density would have produced an _ 3 observable anomaly. An upper limit of 2.70 g cm for the pendants is consistent with data from field samples and Oh _ 3 (1971) which indicate a density of 2.70 +_ 0.01 g cm for limestones and marbles from the southwestern Tehahcapi Mountains. It is also consistent with data for limestone pendants elsewhere in the Sierra Nevada which have densites _ 3 of approximately 2.66 g cm (Oliver and Robbins, 1982). The Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon pendants are lithologically different from the La Liebre and Bronco Canyon pendants. The La Liebre and Bronco Canyon bodies are principally marble and minor schist and quartzite whereas the northeastern group have lower carbonate content and larger amounts of clastic rocks and schist. Volcanic rocks (metabasalt, metafelsite and possible tuff) also occur in the northeast pendants. These lithologic changes result in a higher density for the northeastern pendants. Modeling of the northeastern pendants indicates that a _ 3 density contrast of <0.1 g cm between the pendants and the enclosing plutons. This suggests a bulk density of 2.75 -3 g cm for the Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon pendants, which is consistent with data from pendants in the Sierra Nevada (Table 2). Pendants 93 composed of metavolcanics , schists, and hornfels in the _ 3 Sierra Nevada have densities of 2.65-2.84 g cm (DuBray and Oliver, 1981; Oliver 1977; Oliver and Robbins, 1982). The eastern prong of the Tehachapi pendant exhibits a positive closed-contour anomaly having an amplitude of 5 mgal that reaches a maximum value of -85 mgal. The central and western arms of the pendant are separated by a 2 mgal low next to J (Figures 9 and 11) over the granodiorite of Claraville. The westernmost prong exhibits only a slight deflection of the isogals (K in Figure 11) suggesting a residual anomaly of 1-2 mgals. The Tehachapi pendant is composed of schists, quartzites, hornfels and marble (Dibblee and Louke, 1970; Dibblee and Warne, 1970). It is bounded by granite of Tehachapi Airport on the east, the granodiorite of Claraville in the center, and the tonalite of Bear Valley Springs on the west. These plutons decrease in density _ o _ o eastward, from 2.74 g cm for the tonalite to 2.59 g cm for the granite, producing a density contrast across the _ 3 region of 0.15 g cm . Modeling of the Tehachapi pendant, based on geometric data from Dibblee and Louke (1970), indicates a density of _ 3 2.76 g cm for the pendant, consistent with densities for such pendants elsewhere in the Sierra Nevada (Table 2). _ 3 This density produces a contrast of 0.08 - 0.15 g cm with the surrounding plutons, indicating that the anomaly is 94 controlled largely by the low densities of the enclosing plutons. The Brite Valley pendant exhibits a complex gravity anomaly. In the filtered data (Figure 11) the pendant is indicated by a deflection of the isogals at L. Higher resolution hand-contoured maps (Figures 14 and 15) show more detail but a similar pattern. North of Brite Valley the pendant exhibits no anomaly whereas to south it exhibits an anomaly of 1—3 mgal as indicated by the deflection of the isogals. The western side of the pendant displays a larger anomaly than does the eastern side (Figure 14 and 15) which is consistent with the outcrop pattern. On the west side of Brite Valley, the pendant is approximately 1 km wide whereas on the east side it is only 0.5 km in width. Modeling of the pendant and Brite Valley indicates that the 100-200 m of alluvium within the valley is largely responsible for the observed minimum. A density of _ o approximately 2.84 g cm , which produces a density _ 3 contrast of only 0.1 g cm with the enclosing tonalite of Bear Valley Springs, is also indicated. In summary, modeling of the pendants of the Tehachapi Mountains suggests that they are relatively shallow having vertical dimension of 300-2000 m. These values are on the small side of the size range for pendants elsewhere in the Sierra Nevada (Oliver, 1977; DuBray and Oliver, 1981; 95 Oliver and Robbins, 1982). Sufficently dense gravity data was not obtained over the pendants to allow detailed modeling to determine more precise dimensions. Calculated densities for the La Liebre and Bronco _ o Canyon pendants are 2.66-2.72 g cm consistent with being largely marble. The Cottonwood, Gamble Spring, Bean Canyon and Oak Creek Canyon pendants have slightly higher -.3 calculated densities of approximately 2.77 g cm as they have minor volcanic rocks and an increased amount of schist. Densities for the Brite Valley and Tehachapi _ 3 pendants are 2.76-2.8 g cm , consistent with a predominately schist composition. Gravity studies in the Sierra Nevada indicate that pendants display both positive and negative anomalies, depending on their composition and that of the surrounding rocks (Oliver et a1., 1961; Oliver, 1977; DuBray and Oliver, 1981; Oliver and Robbins, 1982 ; Hanna e t al . , 1974 a,b). Metasedimentary rocks range in density from 2.3-2.76 — 3 — 3 g cm J and average 2.75 g cm (Oliver, 1977). Pendants of _ 3 metavolcanic rock have higher densities of 2.60-3.14 g cm _ o and average 2.85 g cm . Densities of pendants in the Tehachapi Mountains are typical of metasedimentary p enda nt s. 96 d. TONALITE OF BEAR VALLEY SPRINGS Two positive anomalies and one negative anomaly are observed within the tonalite of Bear Valley Springs (anomalies C, B, and D, Figure 14). Anomaly A is a broad north-northeast-trending low having an amplitude of approximately 2 mgal. The high at C has approximately 2 mgal of closure and 3-4 mgal of overall amplitude. A second high at B has about 2 mgal amplitude and trends northeast, west of Cummings Valley. There are no major structural or lithologic changes in the area to produce these anomalies. However, two subtle aspects of the tonalite's composition may be responsible for the anomalies; mineralogic variations or the frequency of xenoliths. The data of Ross ( 1985a) indicate that hornblende and biotite make up a considerable fraction of the tonalite, respectively 11 +_ 4.3% and 12.5 3.4%. These two minerals _ 3 have high densities; hornblende 3.0-3.4 g cm and biotite _ 3 2.8-3.2 g cm and there is a correlation between the density of the tonalite and the percentage of these minerals. Variation of a few percent in the amount of hornblende and biotite will result in a change of a few percent in the bulk density of the rock. A variation of +4% in hornblende _ 3 content will produce a density contrast of +0.02 g cm • This contrast can, depending on the volume involved, 97 produce a significant gravity anomaly. Modeling indicates that an anomalous region of a few square kilometers in area extending to a depth of a few kilometers can produce an anomaly of >1 mgal. The low at A corresponds to an area of low hornblende content (<10%) and normal biotite. The high at C is associated with above normal hornblende (14-17%) and biotite contents. Similarly, the high at B correlates with a local increase in the hornblende content, although the control is not as good. The gravity anomalies observed within the tonalite can, therefore, be explained by variations in the amount of hornblende and biotite A second possibility relates to the amount of mafic xenoliths in the tonalite. Because of their mineralogy, the inclusions have a higher density than pure tonalite (2.90 — 3 vs. 2.74 g cm ). Local highs and lows could correspond to variations in the subsurface distribution of xenoliths. There is, however, no data on the frequency of xenoliths to assess this possibility. e. TERTIARY ROCKS NORTHEAST OF TEHACHAPI VALLEY Tertiary volcanic and clastic rocks; the Bopesta, Kinnick and Winet Formations, crop out northeast of Tehachapi Valley. These units are characterized by a gravity low indicated by the deflection of the isogals at K and the closed low at L (Figure 9). 98 Filtering of the data (Figure 11) enhances these anomalies, forming the lows at M and N. The outline of the gravity low corresponds to the outcrop pattern of the Tertiary rocks. A northeast striking syncline occurs in the southernmost area whereas a more circular basin centered under Cache Peak occurs farther north (Dibblee, 1967; Dibblee and Louke, 1970). The anomaly over the northeast trending syncline exhibits 2 — 4 mgal of closure and an overall amplitude of 6—8 mgal, including the deflection of the surrounding isogals (M in Figure 11). The basin at N has 4-6 mgal of closure and an overall amplitude of 6-8 mga 1. Modeling of the syncline, based on map data of Dibblee (1967) and Dibblee and Louke (1970), indicates a density contrast of -0.1 g cm Thicknesses of 1500 - 2000 m of rock are sufficient to produce the observed 8 mgal anomaly for the basin. The syncline has a similar density contrast of -0.1 to -0.12 g cm"^. _ Q The modeled density contrasts of -0.1 to -0.12 g cm , indicate densities of the Tertiary volcanics and elastics _ o are 2.49 to 2.55 g cm . These values are on the high side of the samples of sandstone, tuff and basalts collected in Sand Canyon. However, only a limited amount of data is available. The values are typical of the Tertiary volcanics observed elsewhere in southern California (Table 2). 99 f. ANTELOPE VALLEY The western Antelope Valley is characterized by an east-west trending low at E (Figure 9) lying south of the southwestern foothills of the Tehachapi Mountains and north of the Antelope Buttes. The low reaches a level of -121 mgal and has an amplitude of approximately 20 mgal. Gradients around the margin of the low are largest on the southern and northwestern sides, being 4 mgal/km. Within the anomaly, gradients decrease to approximately 1 mgal/km. Northeastward, the gradient is only 0.7 mgal/km as the gravity increases into a saddle separating the low at E from smaller low to the northeast at F. Two additional lows occur in the Rosamond-Mojave area at F and G (Figure 10). Both of these lows have 4-6 mgal of closure and flanking gradients of 1-2 mgal/km. Anomaly F lies north of Willow Springs in the region between two outcrops of Tertiary volcanics and anomaly G lies west of Soledad Mountain. Mabey (1960) discussed the gravity of the Antelope Valley and suggested that these anomalies result from thick sections of basin-filling Tertiary clastic and volcanic _ 3 rocks. Mabey estimated a density contrast of 0.3—0.4 g cm which indicated thicknesses of 1000-3000 m for these basin- filling rocks. A more detailed discussion of these features is presented by Mabey (1960). 100 3. FAULTS a. GARLOCK—PASTORIA FAULT SYSTEM The Garlock-Pastoria fault system forms a boundary between the hlgh-density metamorphic rocks to the north and low-density granitic plutons to the south (Figure 2). Southwest from the head of Tejon Canyon to the intersection of the Garlock and Pastoria faults, the Garlock fault acts as the lithologic boundary. Farther southwest, the Pastoria fault separates the metamorphic and granitic rocks. The juxtaposition of these two differing rock types across the _ 3 faults results in a density contrast of up to 0.45 g cm The Garlock fault itself is not apparent in the contoured data (Figures 9 and 12) because of the large gradient into the Antelope Valley. However, band-pass filtering of the data reveals the fault's presence (Figure 13). North of the faults, gradients within the metamorphic terrane are approximately 2 mgal/km whereas to the south they are about 1 mgal/km and locally as low as 0.5 mgal/km. Northeast of Tejon Canyon, similar granitic rocks are juxtaposed on both sides of the Garlock fault, hence there is no anomaly because of the lack of a density contrast. The Garlock and Pastoria faults are marked by a large gravity gradient and separating regions having gravity differences of 16-18 mgal. As the Garlock fault extends 101 westward from its intersection with the Pastoria fault, through the granitic plutons, it is not characterized by a gravity anomaly (Figure 13). Based on geologic and geochemical data, Sharry (1981) suggested that the Pastoria fault was the original westernmost extension of the Garlock fault and that it took up most of the lateral movement which is classically associated with the Garlock fault. Further, he argued that the thrusting on the Pastoria fault and the formation of the western strand of the Garlock fault are recent developments that have occurred in response to the stresses induced by the San Andreas fault. Sharry believes that the Garlock—Pastoria fault zone acts as a fundamental crustal discontinuity in the Tehachapi Mountains. b. WHITE WOLF FAULT The White Wolf fault, despite the impressive amount of vertical displacement across it (3-4 km), is not apparent in the gravity data (Figure 9). Along most of its length, isogals trend at high angles across the strike of the fault. Only near Commanche Point do the isogals parallel the fault and exhibit a 2-3 mgal/km northward gradient, but this is unrelated to the fault. The absence of a well-defined anomaly along most of the fault's length results from the large amount of 102 displacement across the fault and the lack of a significant near-surface density contrast. Modeling of the fault with 5 km of sediment to south and 9 km north of the fault, indicates that the resulting gravity anomaly has a wavelength of about 40 km. The modeled anomaly is simply a northward gravity decrease having a gradient of 1-2 mgal/km. Such a gradient is not incompatible with gravity in the southern San Joaquin Valley, but the anomaly is masked by more complicated density contrasts of the surrounding area. Farther northeast along the fault, where sedimentary cover is thin or lacking, the absence of an anomaly results from the lack of a density contrast across the fault. Tonalite of Bear Valley Springs crops out continuously south of the fault between the Tejon Hills and Caliente. North of the fault, the tonalites of Bear Valley Springs and Mt. Adelaide and miscellaneous mafic and ultramafic rocks either crop out (Figure 1) or are buried by a thin sedimentary cover (Ross, 1980; May and Hewitt, 1948). 4. THE INTERMONTANE VALLEYS Contoured and filtered data for the range as a whole (Figures 9 and 11) show little detail associated with any of the intermontane valleys. A northeast gradient of <1 mgal/km and northwest trending isogals characterize the 103 valley region. The absence of an anomaly over the valleys (Figure 9) results from the 4 km grid spacing which is too large to reveal the fine structure of the gravity field that might be associated with the valleys. In an effort to determine if any gravity anomalies were present, hand—contoured maps of smaller areas around the valleys were prepared (Figures 14 and 15). Computer gridding failed to produced useful contour maps because of the uneven data distribution. However, hand contoured maps for the regions around Bear and Cummings Valleys (Figure 14) and western Tehachapi and Brite Valleys (Figure 15) show considerable detail. a. BEAR VALLEY Bear Valley is actually composed of three separate small valleys. Upper, Middle and Lower Bear Valleys, are, 2 2 respectively, the eastern (1.7 km ), central (5.0 km ), o and western (4.5 km ) valleys (Figures 1 and 14). Cummings Valley lies to the southeast and is much larger, 2 approximately 40 km . All of these are flat alluviated valleys within the surrounding tonalite of Bear Valley Sp rings• Gravity within the tonalite of Bear Valley Springs is characterized by a northeast trending gradient of <1 mgal/km (Figure 14). None of the valleys exhibit clearly 104 defined anomalies. Lower and Middle Bear Valleys (D and E in Figure 14) may have residual lows of 0.5 mgal, based on deflections of the isogals. Upper Bear Valley (G in Figure 14) displays no indication of any anomaly. The only significant anomaly is associated with a bedrock ridge (E) that separates the lower and middle valleys. A deflection of the isogals suggests an anomaly of 1 mgal relative to the adjacent valleys. Seismic data (B.S.K. and Associates, 1981) indicate that the ridge at E is bounded on the northeast and southwest sides by faults. The tight paralleling of the isogals along the edge of the ridge is consistent with faulted boundaries. The same seismic data also suggests that the alluvium in Middle Bear Valley, north of the ridge, is 50-60 m thick. Modeling indicates that for 50—60 m of alluvium to produce the observed 0.5 mgal anomaly, it must have a o density contrast of -0.25 to -0.3 g cm . This would _ 3 indicate the alluvium has a density of 2.44-2.49 g cm , which is on the high side for alluvium reported elsewhere in southern California (Table 2). _ o Assuming the same density contrast of —0.25 g cm for the alluvium, the thickness of fill in Upper and Lower Bear Valleys can be estimated. Lower Bear Valley displays an 0.5 mgal low which would suggest 50 m of alluvium. Upper Valley has no observable anomaly indicating alluvium <50 m thick. 105 b. CUMMINGS VALLEY Cummings Valley exhibits a well-defined gravity low at H (Figure 14), The isogals closely parallel the valley margin except at the northeast end where they indicate a secondary low at J. The low at H trends northeast and reaches -76.21 mgal. The closure of the low (the -76 mgal contour) is offset to the northwest of the valley's longitudinal axis though additional contours define a more symmetric anomaly. Gravity relief, relative to the valley edge, is 2-3 mgal. Data of Michael and Me Cann ( 1962) suggest that the alluvial thickness in Cummings Valley is asymmetric with the thickest accumulations (150 m) occurring on the northwestern side of the valley against a northeast striking fault. Modeling of the valley using the thickness data of Michael and Me Cann (1962) suggests that the _ o alluvium has a density contrast of -0.5 to -0.6 g cm , _ 3 indicative of a bulk density of 2.14 to 2.24 g cm • The estimated density is consistent with other data for alluvium (Table II) although the density contrast is quite high. Northeastern Cummings Valley is marked by a semicircular low at J which reachs -78.22 mgal and has an amplitude of 2-3 mgal (Figure 14). Gradients along the 106 edges of the low are 2-3 mgal/km. This anomaly is separated from the low at H by a saddle which stands about 0.5 mgal higher. An abrupt termination of the low against the base of the mountain is indicated by isogals (_<80 mgal) which are not distorted. The northeast edge of the anomaly appears to be controlled by a fault which forms the northeastern edge of the valley (Dibblee and Warne, 1970). The low suggests that a locally down-dropped block has formed along the fault and is covered by 100-200 m of alluv ium• c. BRITE VALLEY 2 Brite Valley is a small, 8 km , valley lying within the Brite Valley pendant. It is characterized by a gravity low offset to the northeast side of the valley with two closed-cont ours and 2-3 mgal of relief (K in Figure 15). The lowest gravity observed in the valley was -80.46 mgal. Michael and McCann (1962) indicate that the alluvial fill within Brite Valley is asymmetric, thickening northeastward to a maximum of 150 m along a northwest trending fault at the valley's edge. Modeling suggests that 150 m of alluvium having a density contrast of -0.5 to -0.7 _ O g cm J will produce the observed anomaly. This contrast indicates the alluvium has a bulk density of 2.04-2.24 g — 3 cm . Similar to the situation in Cummings Valley, the 107 indicated densities are comparable to other areas but the density contrast is quite large. d. TEHACHAPI VALLEY Tehachapi Valley is the largest of the intermontane o valleys, being approximately 96 km • Figure 15 indicates that western Tehachapi Valley is dominated by a northwest trending gravity low at M. The low trends N65°W as it passes beneath the town and then N30°W as it extends toward Tehachapi Canyon. Southeastward it broadens and descends into the lows north and south of the valley. The low is asymmetric, the north side having larger gradients than the south, respectiv1ey, 4-5 mgal/km compared to 6-8 mgal/km. Gradients along the axis are low, <1 mgal/km. Most of Tehachapi Valley is floored by recent alluvium. However, older alluvium, the Tehachapi Formation, and Miocene volcanic and clastic rocks are exposed in the northwestern end of the valley (Lawson, 1906; Buwalda, 1954; Dibblee and Louke, 1970). The attitudes of these units define a northwest trending syncline which opens southeastward and this structure is reflected in the gravity. The steep dips of the rocks on the northeast side of the syncline are consistent with the higher gravity gradients, relative to the southwest side. The asymmetry results from a northwest striking normal fault along the 108 north side of the structure which has deformed the syncline (Dibblee and Louke, 1970)* Modeling of the structure using a density contrast of -3 -3 -0.25 g cm for the alluvium and -0.34 g cm for the synclinal sediments reproduces the observed anomaly. The model suggests that the older sediments have densities of _ o about 2.4 g cm and that the syncline is about 600 m thick along its axis. The younger alluvium is relatively thin (50 m) and does not contribute significantly to the observed anoma1y. Lawson (1906), Buwalda (1954) and Dibblee and Louke (1970) have noted that the Cache Creek drainage is more mature than the Tehachapi Creek drainage. They proposed that the valley originally formed by tectonic warping and was enlarged by erosion; the debris being carried eastward out into the Mojave Desert through Cache Creek Canyon. The syncline, defined by both the geology and gravity, corresponds to the original Tertiary downwarp of the region which formed the proto-Tehachapi Valley. The wide variation in the calculated densities for the material filling each valley results from the lithologic differences of that material. Considerable water-well data (J. Ott, Tehachapi Cummings Water District, personal communication, 1984; J. Geary, Bear Valley Community Services District, personal communication, 1984) indicate that the material in Cummings, Brite and Tehachapi Valleys 109 is largely clay to silty-clay and isolated layers of sandy clay, sand and gravel. In contrast to these fine-grained sediments, Bear Valley is filled with much coarser material; sand, silty-sand and gravel. Clay occurs only rarely as thin layers in Bear Valley. The large fraction of very fine material in Cummings, Brite and Tehachapi Valleys _ 3 suggests that a bulk density of 2.14 g cm is not _ 3 unreasonable. A density of 2.45 g cm for the fill in Bear Valley also seems consistent with the lithology of the material. Well data indicate that the clastic material rests on a floor of what is described as "decomposed granite," a catch-all term for crystalline rock so severely weathered that it has been broken down to sand and gravel particles. This layer is 3-30 m thick, below which is weathered and then fresh "granite." The density anomaly calculated for the alluvium probably results from all of the material above the weathered basement rock. The origin of the valleys, wether they are dominately erosional or structural, has been a long standing and unresolved geologic problem (Lawson, 1906; Buwalda, 1954; Michael and Me Cann, 1962; Dibblee and Warne, 1970; Dibblee and Louke, 1970). In general, the valley boundaries which have mapped faults are characterized by asymmetric fills of alluvium and higher gravity gradients. However, the gravity data alone does not add significant insight into resolving the problem of the valleys' origin. 110 E. VERTICAL DERIVATIVES Vertical derivatives are often used in the study of gravity as part of the effort to isolate short—wavelength anomalies from long-wavelength regional affects. Both the first and second derivatives have the potential of enhancing small-scale anomalies because of the large vertical gravity gradients associated with a near-surface source. Generally, the second derivative has been used for this purpose (Telford et al., 1976; Dobrin, 1976). Two vertical derivatives, the 1st (dg/dz) and the 2nd 2 2 (d g/dz ), were computed and contoured (Figures 16 and 17). In both cases the contour maps depict a confusion of anomalies. The first and second vertical derivatives appear largely the same although the amplitudes of the anomalies in the second derivative are larger. Though anomalies isolated by filtering are accentuated in the derivatives, each has developed into multiple features. Anomalies in the derivative field occur wherever there is a gradient change, as on the flanks of small anomalies. As a result each anomaly in the original data develops one or more secondary closed-contour anomalies. These mark any asymmetry in either the gradient or curvature of the field around the original anomaly. Numerous features developed where there was no indication 111 of anomalies in the original or filtered data and where there is no corresponding geologic feature. These probably result from the local variations in the field which are either real and unrelated to surface geology or to noise produced from the gridding of unevenly spaced data. The flanks of the anomalies appear to be bounded by parallel north-south and east-west lineaments. This affect results from the relatively large grid size (4 km) and the the low number of grid points (16) used to produce the contour map. Most of the anomalies in the derivative field are only 1 grid interval across. It appears that the grid number was too small for effective use in the vertical derivatives. A larger grid number was, however, precluded as significant noise was generated by the gridding routine due to the uneven data distribution. Several comments can be made regarding the first vertical derivative map (Figure 16). The metamorphic terrane of the southwestern Tehachapi Mount a ins (A) is well defined and separated from the high over the Tejon Hills to the north (B). The Garlock fault is bounded to the south by a gravity step over the low-density granitic rocks and a large gradient over the metamorphic rocks to the north. In general, the anomalies observed in filtered versions of the data are reproduced in the derivative maps. However, since so many more anomalies which correspond to the local changes in gradient of the gravity field are 112 produced, in addition to the limitations noted above, the vertical derivative is of little use here in the interpretation of the gravity anomalies. F. UPWARD CONTINUATION The gravity data for the Tehachapi Mountains were upward continued to various levels to investigate the persistence of large- and small-scale anomalies. Figure 18 illustrates the gravity field continued upward to 1 km above the datum (sea level). The long- wavelength anomalies, having large amplitudes, remain intact. However, many of the smaller anomalies have partially or completely disappeared and the field is much smoother. The gravity relief across the area has dropped 11% to 59.5 mgal from 67 mgal in the original data. The main Tehachapi Mountain high at A and the northern high at B from Figure 9 are both still resolvable. Additionally, the highs at I, associated with the bedrock outcrop south of the Edison fault, and J, associated with the Tehachapi pendant, still persist although at a subdued level. The lows at L and K, which are associated with the Tertiary clastic and volcanic rocks northeast of Tehachapi Valley, are still evident. Much of the structure within the Mojave Desert also remains. 113 When continued upward 2 km, little structure remains in the gravity data (Figure 19). The two highs (A,B) of the southwestern Tehachapi Mountains have merged and the only other anomaly which remains is the low northeast of Tehachapi Valley (L). Much of the structure within the Mojave Desert has also disappeared. Isogals are smooth and the relief is down to 80% of the original, approximately 53 mga 1. Upward continuation from 5 to 15 km (Figures 20-22) shows a progressive decrease in the detail of the field. At 5 km (Figure 20) only the Antelope Valley low and the broad Tehachapi Mountain high remain. The trend of the isogals becomes more and more northeasterly. At 30 km (Figure 22) the field shows only a southeastward decreasing field across the region. Relief is now <20 mgal, 30% of the original. G. CRUSTAL MODELS 1. METHODOLOGY To quantify the crustal structure of the Tehachapi Mountains and adjacent areas three crustal-gravity models were constructed from closely spaced gravity data (Figures 23—25). Modeling was used to address questions regarding the thickness of the crust beneath the Tehachapi Mountains 114 and the affects of the various major rock bodies and structures on the gravity field. As modeling was conducted to understand the regional properties of the crust, only the major rock—bodies were included in the models. Minor pendants, small plutons as well as patches of alluvium and Tertiary sedimentary and volcanic rocks were excluded. The result is a calculated profile that is slightly smoother than the observed profile and which does not reflect each short-wavelength variation. Crustal models were constructed along northeast trending profiles (Figure 1). Southwest to northeast these profiles include: 1) the Pastoria Canyon profile (Figure 23), from data acquired along the Pardee-Pastoria transmission line; 2) the Tejon Canyon profile (Figure 24), using data taken along the Antelope—Magunden transmission line; and 3) the Tehachapi profile (Figure 25), from data collected along the Bakersfield-Mojave highway. Data collected along the highway was projected onto the straight-line profile used in this model. Data on seismic velocities and crustal thicknesses in the Tehachapi Mountains and southern San Joaquin Valley are lacking. Overall, the velocity structure in the Mojave Desert is better constrained, though only in the central part. As a result, over most of the study area there is little control for the crustal models calculated here. Hence, these models are more speculative than they might otherwise be. 115 The only directly observable inputs to be used in the models are the surface extent of various rock bodies and their near-surface densities. Some control on the shallow sub—surface properties of the San Joaquin Valley sediments is available from drill hole data. Dimensions and densities of crustal bodies at depth must be inferred by extrapolations of seismic data or by analog to studies from other areas• The surface geology used in the models was taken from the maps of Ross (1980, 1985a). Rock densities were obtained from field sampling and the literature (Table 2). Subsurface crust and mantle densities were estimated from the ve1ocity-density relationship presented by Hill (1978), which is a combination of the work of Birch ( 1960), Nafe and Drake (1963), and Bateman and Eaton (1967). The velocity structure of the central Mojave Desert has been extensively studied (Press, 1960; Roller and Healy, 1963; Gibbs and Roller, 1966; Prodehl, 1970, 1979; Hileman, 1979; Hearn, 1984). That work focused on an area somewhat distant from the Tehachapi Mountains, but those data were used as a starting point for the models. Velocity models for the Mojave vary in detail but in general show an upper layer (0 — 5 km) having velocity of 5.5 km sec ^ _ 3 (density = 2.65 g cm ), an intermediate layer (5 to 20-25 km) having a velocity of 6.1—6.3 km sec ^ (density = 2.8 g — 3 — 1 cm ) and a lower crustal velocity of 6.8 km sec (density 116 _ o = 3.0 g cm ). Mantle velocities range from 7.8 to 8.1 km -1 — 3 sec indicating a density of approximately 3.25 g cm Crustal velocity data in the southern San Joaquin Valley is lacking. A poorly constrained refraction profile from Prodehl ( 1979), data from Page e t al. ( 1979 ), Wentworth e t a 1 . ( 1983), Oppenheimer and Eaton ( 1984) and W. Mooney (U.S. Geological Survey, personal communication, 1985) provided velocity data for the valley near latitude 36°, north of the study area. Data for the Great Valley suggests a heterogenous structure but in general; an upper layer (0 to 5-7 km) having a velocity of 2.5-2.8 km sec ^ _ 3 (density = 2.17—2.3 g cm ), an intermediate layer (5-7 to 12-21 km) having a velocity of 5.0 to 6.2 km sec ^ (density _ 3 = 2.6-2.8 g cm ) and a lower crustal layer (12-21 to 26 km) having velocity of 6.0 to 6.1 km sec ^ (density = 3.0- — 3 — 1 3.1 g cm ). Mantle velocities were 7.9-8.5 km sec _ 3 indicative of densities of 3.25 to 3.4 g cm . This data was then extrapolated to the southern San Joaquin Valley for use as a starting point. Seismic data from the Sierra Nevada batholith suggests an upper crustal layer having velocity of 4.3-6.0 km sec"^ — Q (density = 2. 63 — 2 . 75 g cm ) extending to a depth of 5 — 10 km, an intermediate layer from 5-10 km to 20-30 km having a — 1 —. Q 6.0-6.4 km sec velocity (density = 2.75-2.85 g cm ) and a lower crustal layer below 20-30 km having a velocity of 6.51-6.7 km sec * (density = 2.9-3.02 g cm ^). 117 There are no seismic refraction data within the Tehachapi Mountains making it impossible to estimate subsurface densities from velocity. The only data which does exist are some broad constraints on the crustal thickness. P—wave delay studies of Hearn (1984) and contouring of seismic refraction results from surrounding area by Prodehl (1970, 1979) suggest crustal thicknesses of 30-34 km in the Tehachapi Mountains, a thickening of the crust by a few kilometers relative to adjacent areas. The data discussed above were used as a starting point for the modeling. In order to fit the observed and calculated gravity values various parameters (density and vertical dimensions of crustal layers) were varied in an iterative manner in subsequent models. Both density and vertical extent of different layers were changed until the best fit was obtained. Because some velocity control existed in the San Joaquin Valley and Mojave Desert the dimensions and densities of these layers were allowed to vary less than those for the Tehachapi Mountains. The final models are illustrated in Figures 23—25 and schematic crustal columns for each of the three provinces (San Joaquin Valley, Tehachapi Mountains and Mojave Desert) are illustrated in Figures 26-28. Densities for the various crustal layers are listed in Tables 3-5. An interpretive geologic cross section for the Tejon profile is shown in Figure 29. 118 _ o 2.72 g c m ( T a b l e s 3-5), c o n s i s t e n t w i t h s a m p l e d a t a ( T a b l e 2). U n d e r l y i n g t h e g r a n i t i c s a i s t e n k i l o m e t e r t h i c k l a y e r ( d e n s i t y = 2.75 g c m ) w h i c h r e p r e s e n t s a p o s s i b l e i n t e r p r e t a t i o n o f t h e P e l o n a s c h i s t , w h i c h m a y u n d e r l i e m u c h of t h e M o j a v e D e s e r t ( C h e a d l e e t a l . , 1984 , 1985). B e l o w t h e P e l o n a s c h i s t i s a 10-15 k m t h i c k l a y e r o f _ o l o w e r c r u s t a l r o c k s h a v i n g d e n s i t i e s o f 2.89-2.95 g c m . T h e c o m p o s i t i o n o f t h e s e r o c k s i s u n c e r t a i n b u t t h e y p r o b a b l y r e p r e s e n t s u b d u c t e d o c e a n i c c r u s t . T h e s e r o c k s w o u l d t h e n r e p r e s e n t t h e o c e a n i c c r u s t a n d r e p r e s e n t s t h e b a s e m e n t o n w h i c h t h e s c h i s t p r o t o l i t h w a s d e p o s i t e d . B e l o w 30-32 k m i s t h e m a n t l e , d e n s i t y 3.25 g c m ~ ^ . T h e c r u s t a l c o l u m n m o d e l e d h e r e is s i m i l a r t o t h a t d e r i v e d f r o m s e i s m i c r e f r a c t i o n i n t h e c e n t r a l M o j a v e D e s e r t ( F i g u r e 26). B o t h s e c t i o n s h a v e a l o w - d e n s i t y u p p e r c r u s t a l l a y e r o v e r l a i n b y v a r i a b l e t h i c k n e s s e s of a l l u v i a l c o v e r a n d a d e e p h i g h - d e n s i t y c r u s t . T h e m a j o r d i f f e r e n c e b e t w e e n t h e m o d e l s l i e s i n t h e p r o p e r t i e s o f t h e m i d - c r u s t a l l a y e r . M o d e l i n g h e r e s u g g e s t s t h a t t h e c r u s t a d j a c e n t t o t h e T e h a c h a p i M o u n t a i n s i s m o r e s t r u c t u r e d , l e s s d e n s e a n d t h i c k e r t h a n i n t h e c e n t r a l M o j a v e . C o n s i d e r i n g t h e h e t e r o g e n e o u s g e o l o g y o f t h e M o j a v e D e s e r t ( D i b b l e e , 1967; B u r c h f i e l a n d D a v i s , 1981) m i n o r v a r i a t i o n s i n c r u s t a l s t r u c t u r e a r e n o t s u r p r i s i n g . Modeling of the San Joaquin Valley indicates a crustal thickness of 27-29 km (Figure 27). The thickest crust (29 119 Several regional and some local conclusions can be drawn from the modeling in regard to the character of the crust in and adjacent to the Tehachapi Mountains. The general results are presented first, followed by details of each of the three profiles. 2. REGIONAL IMPLICATIONS Modeling indicates that the crust beneath the Tehachapi Mountain block is several kilometers thicker than beneath either the San Joaquin Valley or Mojave Desert. A crustal thickness of approximately 35 km is indicated by the modeling; 3-5 km thicker than the Mojave Desert and 5-8 km thicker than the San Joaquin Valley. Along the trend of the Tehachapi Mountains there does not appear to be a significant variation in thickness. A thick crust beneath the Tehachapi Mountains, relative to the adjacent areas is required to satisfy the observed gravity profiles unless significant changes are made to the crustal densities used for the San Joaquin Valley and Mojave Desert blocks. Although such changes might be made, they would indicate fundemental changes of the crust beneath the San Joaquin Valley and Mojave Desert as the Tehachapi Mountains are approached. There is no evidence to suggest that such changes occur. 120 The nature of the crustal thickening beneath the Tehachapi Mountains is not resolvable from modeling. An abrupt crustal thickening at the edges of the range or a gradual thickening over a few kilometers from the San Joaquin Valley and Mojave Desert toward the range will produce similar gravity signatures. The White Wolf fault, bounding the range on the north, and the Garlock fault, which cuts through the range, are major structural boundaries having appreciable vertical and horizontal displacement. Hence, an abrupt crustal thickening is possible along these faults. Isostatic compensation of a mountain range, on the other hand, usually occurs on a regional scale and suggests that the crustal thickening may be more widespread than directly under the range. Crustal thickness in the Mojave Desert is modeled as being 31—32 km, excluding the local thickening near the range (Figure 26). This is consistent with estimates of crustal thickness based on seismic refraction data (Press, 1960; Roller and Healy, 1963; Gibbs and Roller, 1966; Prodehl, 1970,1979; Hileman, 1979; Hearn, 1984). The crust has been modeled as consisting of four major layers, in addition to a variably thick surficial alluvial cover. The upper two crustal layers represent the granitic rocks exposed along the south flank of the Tehachapi Mountains and in isolated bedrock mountains scattered across the Mojave Desert. These rocks have model densities of 2.63 - 121 km) occurs along the northeast profile (Tehachapi profile). It thins to 27 km along the Te j on Canyon profile and then thickens to 29 km at the Pastoria Canyon profile. The models are not particularly sensitive to changes in crustal thickness on the order of 1—2 km. However, the pattern of crustal thicknesses is consistent with a thicker crust near the valley margins relative to the center of the valley, a pattern indicated by seismic refraction data near 36° latitude (Oppenheimer and Eaton, 1984 ; Holbrook e t al. , 1985; W. Mooney, personal communication, 1985). The San Joaquin Valley crust was modeled as having four layers (Figure 27). Uppermost are variably thick (<5 km) low-density, low—velocity sediments. Below the sediments and extending to the base of the crust are three additional layers of increasing density. Lithologic information is available in only a few locations near the Tehachapi Mountains and only for the material which directly underlies the sediments. Drill-hole data (May and Hewitt, 1948; Ross, 1985a) suggest that the sub-sediment basement is composed of both plutonic rocks (presumably equivalent to the tonalite of Bear Valley Springs and Mt. Adelaide) and metamorphic rocks (equivalent to the metamorphic terrane exposed in the southwestern part of the range). The densities of the deeper layers are based on seismic refraction data. The deep crust may represent a section of schist, analogous to the Pelona schist (density 122 _ o = 2.75 g cm ), underlain by a high—density lower crustal _ 3 layer which is oceanic crust (density = 2.955 g cm )• The crustal columns derived from the model (Figure 27) are similar to that of the average of several columns from different parts of the San Joaquin Valley (Pakiser, 1963; Eaton, 1963, 1966; Thompson and Taiwan!, 1964 a,b; Prodehl, 1970, 1979; Carder e t al. , 1970; Carder, 1973; Page e t al. , 1979; Wentworth et al. , 1983; Oppenheimer and Eaton, 1984; Holbrook e t al. , 1985). This similarity suggests that the crustal structure of the San Joaquin Valley does not change significantly along the length of the valley with the possible exception of local thickening along the edge of the Tehachapi Mountains. The crustal column for the Tehachapi Mountain block (Figure 28) is largely speculative. No refraction data is available to provide estimates on the seismic velocity and therefore the density of the rocks. The only constraints imposed on the possible structure come from the structures of the San Joaquin Valley and Mojave Desert. If the crustal structures for the San Joaquin Valley and Mojave Desert discussed above are assumed to be correct, then the possible variations for the Tehachapi Mounatin block are limited. However, if those structures are discounted, then the problem is completely unconstrained. The crust for the Tehachapi Mountains is modeled as being composed of three major crustal layers and several 123 local near-surface lenses. The three major crustal layers — 3 — 3 have densities of 2.76-2.8 g cm and 2.75 g cm , and 2.89-2.94 g cm ^ (Tables 3-5). Locally north of the Garlock fault and along the length of the range south of the fault, a low-density surface lense is present. This lense is approximately 5 km thick and corresponds to the low—density plutons (granites and granodiorites) exposed there. The main upper crustal layer has a density of approximately — 3 2.76 g cm and is suggested to be the tonalite of Bear Valley Springs or its compositional equivalent. The two deep crustal layers represent a section of Pelona schist (as exposed between the branches of the Garlock fault) about 10 km thick and oceanic crust. The modeled crustal column for the Tehachapi Mountains is quite different from that of the Sierra Nevada. Seismic refraction studies of the Sierra Nevada (Eaton, 1963, 1966; Pakiser, 1963; Thompson and Talwani, 1964 a,b; Carder e t a1., 1970; Prodehl, 1970, 1979;. Carder, 1973; Warren and Healy, 1973; Pakiser and Brune, 1980) suggest four crustal layers. However, in the Tehachapi Mountains only the uppermost crust is comparable to the Sierra Nevada structure. The important difference is that the deep crust of the Tehachapi Mountains represents the schist and oceanic crust subducted along the Mesozoic subduction zone. The deep crust of the Sierra Nevada, on the other hand, represents the deep levels of the batholithic complex. 124 The Tehachapi Mountain block appears to represent an oblique cross-section through the the Sierra Nevada batholith. The uppermost, low-density granitic portion of the Sierra Nevada section is represented in the Tehachapi Mountains by the granites and granodiorites which are exposed near the town of Tehachapi and along the length of the range south of the Garlock fault. Progressively deeper structural levels are exposed southwest from the tonalite and transitional rocks of Tej on Canyon to the metamorphic terrane. Overall, the Tehachapi Mountains represent a deeper structural level than is exposed in the Sierra Nevada to the north (Sharry, 1981; Ross, 1985 a,b). These crystalline rocks extend to about 10-15 km below which they have been sheared off by unde rthrus ting of the Pelona schist and oceanic crust. 3. LOCAL IMPLICATIONS a. TEHACHAPI PROFILE The Tehachapi profile (Figures 1 and 23) extends from the southernmost part of the San Joaquin Valley across the White Wolf fault, through the tonalite of Bear Valley Springs, Tehachapi Valley and into the Mojave Desert. At the western end of the profile, the high at A results from a body of undiffentiated mafic metamorphic 125 rocks (Dibblee and Chesterman, 1953; Ross, 1980) within the tonalites of Bear Valley Springs and Mt • Adelaide, This body, bounded to the northeast by the Edison fault, has a — 3 density of 2.77 g cm • The steep gradient to the north results from the juxtaposition of low—density Tertiary rocks which fill a basin north of the Edison fault against the high-density basement rocks (Dibblee and Chesterman, 1953), Over the White Wolf fault, the low observed in the gravity at B can not be modeled based on surface geology. It has been duplicated only by the insertion of small body (body 6 in Figure 23) having a density contrast of -0.08 g _ 3 cm • This body may represent a sliver of lower density granitic material incorporated during faulting, although its nature is uncertain. Along the remainder of the profile, gravity decreases toward the Mojave Desert. This gravity gradient results from a decrease of the density of the plutonic rocks exposed at the surface in the range and the low-density crust in the Mojave Desert. Modeling suggests that the plutons surrounding Tehachapi Valley; the granite of Tehachapi Airport and the granodiorite of Claraville, extend to a depth of only a few kilometers. Such a thickness is similar to the Sierra Nevada where seismic refraction data (Figure 28) indicate the low—density layer extends to approximately 5 km. 126 Locally along the profile, several short—wavelength variations are observed which are not matched in detail by the calculated profile. These represent the effects of local alluvial fills and isolated patches of Tertiary rock, along and adjacent to the profile. Density variations within different rock bodies can also induce short- wavelength variations. b. TEJON CANYON PROFILE The Tejon Canyon profile (Figures 1 and 24) crosses the tonalite of Bear Valley Springs, the transitional rocks of Tejon Canyon, the plutons south of the Garlock fault and then extends into the Mojave Desert. Gravity varies smoothly across the profile. An increase in the gravity gradient on the northwest end of the profile at A is associated with the White Wolf fault. Approximately 1 km of low-density sediments occur in the San Joaquin Valley at this point which, combined with the offset of deep crustal layers, produce a density contrast across the fault. Another large gravity gradient occurs on the south side of the range at B. Because the low—density plutons south of the Garlock fault are juxtaposed against the Tehachapi Mountains basement, a deep-seated density contrast results. This contrast is enhanced by the low density of the upper crust of the adjacent Mojave Desert. 127 Between the branches of the Garlock fault, the Pelona schist crops out as a sliver a few kilometers wide. Samples from this area indicate a density of approximately 2.75 — _ 3 2.80 g cm , similar to data for the Franciscan rocks (Stewart and Peselnick, 1977). Modeling indicates that this body forms a variably thick layer at depth extending beneath the length of the range. c. PASTORIA CANYON PROFILE The Pastoria Canyon profile (Figures 1 and 25) crosses the southernmost part of the San Joaquin Valley (the Tejon Embayment) then across the metamorphic terrane of the Tehachapi Mountains and into the granitic rocks south of the Garlock fault. Gravity is smoothly varying and has a symmetric high centered over the crest of the Tehachapi Mountains• The southward increase across the southern part of the valley results from the thinning of the sediments towards the range. On the south side of the Tehachapi Mountains, gravity decreases away from the metamorphic rocks toward the low—density granitic plutons. It is these low—density rocks and the thick low-density crust that are responsible for the observed gradient. In the southwest part of the Tehachapi Mountains, the granodiorite of Lebec (body 7 in Figure 2 5) is in contact 128 with the metamorphic terrane along the Pastoria fault. The Pastoria fault has been interpreted as a thrust fault (Crowell, 1952) and as a strike-slip fault (Sharry, 1981). Modeling indicates that, regardless of the original nature of the fault, only a small wedge of granodiorite lies on top of the metamorphic terrane. The Pastoria fault can not extend deep into the crust if at depth it separates low- density granitic rocks from high-density metamorphic rocks as it does at the surface or as does the Garlock fault. 4. GEOLOGIC CROSS-SECTION ALONG THE TEJON CANYON PROFILE A possible interpretation of the geology of the crust along the Tejon Canyon profile, derived from the gravity modeling, is illustrated in Figure 29. The cross section was drawn using the surface geology and structure for control, then extrapolating to depth on the basis of the rock densities determined from the gravity modeling as well as assumptions of the regional structure (Sharry, 1981; Davis and Burchfiel, 1981; Ross, 1985a). The crustal sections for the three major provinces; the Tehachapi Mountain block, the San Joaquin Valley block, and the Mojave Desert block, have dissimilar near-surface compositions, but are interpreted as having similar lower— crust compositions. 129 The composition of the lower crust is suggested to be composed of a variably thick schist layer overlying oceanic basement. Although probably complexly deformed and locally discontinuous, the schist represents a layer widespread beneath California. Where exposed at the surface, it is referred to as the Rand, Vincent, and Orocopia schists in southern California and the Franciscan complex in the Coast Ranges. These schist bodies and the underlying ocean crust represent remnants of a Mesozoic subduction zone (Burchfiel and Davis, 1981; Blake and Jones, 1981). Presumably, although the geometry is controversial (cf. Ehlig, 1968; Haxel and Dillon, 1978; Crowell, 1981; Burchfiel and Davis, 1981), the schist extends eastward from the areas of outcrop and deepens along the old subduction zone (Page e t al. , 19 79 ; Page , 1981 ) . The San Joaquin Valley contains several kilometers of sediments (Great Valley Sequence and younger) which, in the southermost part of the valley, unconformably overlie a basement of mixed rock types. In the southern part of the valley, basement rocks have been sampled in only a few drill holes (May and Hewitt, 1948; Ross, 1979, 1980, 1985a). That data indicate that both plutonic rocks (tonalite, diorite, and various ultramafic rocks) and metamorphic rocks (metasediments, gneisses and granulites) occur. This basement complex presumably represents the original crust into which batholithic rocks were intruded 130 and samples of those batholithic rocks. Although oceanic crust has been cited as the base of the sedimentary sections farther north in the valley (Bailey et al . , 1970) it is not the basement in the southernmost part. Below about 12 km the remaining crust is suggested to be composed of a thick section of schist and oceanic crust, presumably in tectonic contact with the overlying batholithic rocks. The 8 km of schist in the cross section is based on the 8 km thick model layer having a density of _ 3 2.75 g cm , which is typical of both the Pelona schist from the Tehachapi Mountains (Table 2) and Franciscan rocks (Stewart and Peselnick, 1977). Stewart and Peselnick (1977) suggested that the thickness of the Franciscan rocks east of the San Andreas fault, beneath the San Joaquin Valley, was 12 km. Data presented by Malin e t al. (1981), however, indicate that the schist in Sierra Pelona Ridge may be only 1 km thick. In order for the top of the Franciscan-Pelona rocks to be at a depth of 12 km at the location of the cross section, the Coast Range thrust and its eastward extension would have to dip eastward at 10—15°, an angle which is at least consistent with the orientation of the Moho (Oppenheimer and Eaton, 1984), which presumably represents the base of the oceanic crustal section. This thrust would be equivalent to the Rand and Vincent thrusts exposed in the Mojave Desert and southern California. A mylonite zone 131 probably immediately overlies the thrust, also typical of the Rand-Vincent thrust system. The contact between the schist and the oceanic crust may be depositional or it may be a thrust fault. Seismic reflection studies of the accretionary wedge of the Aleutian and Middle American trench systems typically show that these zones are imbricately deformed by numerous thrust faults (McCarthy and Scholl, 1985; Moore et al., 1979). The Pelona schist, which represents metamorphosed oceanic sediments and locally pieces of the oceanic crust, may have been thickened due the imbricate thrusting as is observed in the wedge of material in current subduction zones. McCarthy and Scholl (1985) suggested that the contact between the base of the sedimentary section and oceanic basement in the Aleutian subduction zone may be a thrust fault which follows the original contact between the two un its. The upper crust of the Mojave Desert is formed by low— density granitic rocks (granites and granodiorites) overlain by up to 2 km (Mabey, 1960) of alluvium and Tertiary sediments. Within the plutonic rocks are scattered metasedimentary pendants of the Bean Canyon Formation, as indicated by the numerous pendants exposed in the Tehachapi Mountains south of the Garlock fault. The granites are truncated at depth by the the Rand thrust, which has been suggested to underlie the Mojave Desert (Cheadle e t al. , 132 1984, 1985). Depth to the Rand thrust varies from zero, in the Rand Mountains, to approximately 10 km near the town of Moj ave• The Pelona-Rand schist is shown as being 10 km thick based on the gravity modeling, similar to the thickness suggested beneath the San Joaquin Valley. Below the schist lies oceanic basement that extends to the base of the c ru s t. The crust of the Tehachapi Mountains is more complicated and speculative. Four different types of rock outcrop along the profile from north to south: tonalite of Bear Valley Springs, transitional rocks in Tejon Canyon, Pelona schist, and the granitic rocks south the Garlock fault. Southwestward through the Tehachapi Mountains consistently more mafic and more highly metamorphosed rocks crop out. This progression includes: (1) granites and granodiorites north of Tehachapi Valley; (2) the tonalite of Bear Valley Springs; (3) the metamorphic and igneous rocks of the Tejon Canyon region; and (4) the metamorphic rocks of the s ou thwes ternmos t part of the range. These different units represent progressively deeper crust, from approximately 10 km (2.5 kbar) north of Tehachapi Valley to 27-32 km (8 kbar) in the southwest (Sharry, 1981; Haase and Rutherford, 1975). This progression suggests that the batholithic terrane has been upended in the Tehachapi Mountains. Presumably these different rock types represent 133 an oblique section through the batholith (Ross, 1985b). The uppermost levels are represented by the granodiorites, granites and tonalites; intermediate levels by the transitional rocks in Tejon Canyon; and deep levels by the metamorphic rocks. The base of the sequence appears to be truncated along a thrust fault, the so-called north branch of the Garlock fault, which has been correlated with the Rand thrust (Ross, 1985 a,b; Sharry, 1981). Along the thrust fault, the rocks of the upper plate have undergone retrograde metamorphism forming a mylonite zone that exhibits a metamorphic grade consistent with conditions exhibited by the schist (Sharry, 1981). The thickness of the schist body is unconstrained by either geologic or seismic data. Modeling does, however, indicate that rocks having density comparable to the schist could extend to depths of 15 to 20 km. Below the schist, by analogy with the models of the San Joaquin Valley, Mojave Desert and Coast Ranges, lies oceanic crust. The density of the lowermost crust of the Tehachapi _ Q Mountains is about 2.89-2.94 g cm , slightly less than the _ o 2.90-2.95 g cm for the modeled oceanic crust beneath the San Joaquin Valley and Mojave Desert. Data on the structure of the oceanic crust (Christensen and Salisbury, 1975) indicate that the density of oceanic crust is variable, — 8 — 3 ranging in density from about 2.4 g cm to 3.1 g cm 134 Significant amounts of uppermost oceanic crust (Layers 1 and 2) containing pillow lavas, dikes, and surfical sediments could have been incorporated into the section in the Tehachapi Mountains to lower the density. Alternatively, the degree of serpentization of the crust could be high. Hess ( 1962) and Christensen and Salisbury (1975) present data indicating a relationship between the percent of serpentization and the density of oceanic crust. Thus, the oceanic crust beneath the Tehachapi Mountains could have incorporated lower density material or retained a higher degree of serpentization than oceanic crust elsewhere in the subduction zone. Alternatively, an entirely different rock type, other than oceanic crust, could form the lowermost crust of the Tehachapi Mountains. Mafic igneous rocks related to the deep levels of the batholith would be compatible with the indicated densities, although their presence would be difficult to explain below the subduction zone. The Tehachapi Mountain section is truncated along both the White Wolf and Garlock faults. Both of these faults represent major crustal discontinuities that extend to the mantle. The Garlock fault has juxtaposed the Tehachapi Mountains against an unrelated piece of the Mojave Desert by 48-64 km of left-lateral strike-slip movement (Davis and Burchfiel, 1973). Crust similar to the Tehachapi Mountains might be expected to occur in the Rand Mountains which were 135 adjacent to the range prior to strike-slip movement on the Garlock fault. The White Wolf fault is a thrust fault and may represent the leading edge of the rotated blocks of the range. Thus it juxtaposes rocks which originally lay in the vicinity of the present northwestern Mojave Desert against a section from the San Joaquin Valley. The Rand thrust, and accompanying Pelona schist and underlying oceanic crust, probably underlie all of the Tehachapi Mountains at some depth. Only along the Garlock fault have the schist and the thrust fault been exposed. The thrust fault probably deepens northeastward as densities typical of the schist and oceanic crust occur at progressively deeper depths in that direction. 5. DISCUSSION OF MODEL RESULTS The gravity models presented here can be analyzed in terms of velocities and time delays. In order to estimate the possible variance of time delays across the region, the travel time for a vertical P-wave from 50 km to sea level was calculated. Average travel time was 7.618 sec. Because of the thick (up to 5 km) section of low-density, low- velocity sediments, the San Joaquin Valley had the longest travel time (7.979 sec). As might be expected, the Tehachapi Mountain and Mojave Desert blocks had shorter travel times because of the small amount or absence of low- 136 velocity sediments. Average travel times for the Mojave Desert and Tehachapi Mountains were 7.628 sec and 7.575 sec respectively. Relative to the mean value, the delay in the San Joaquin Valley would be +0.065 sec, +0.010 sec in the Mojave Desert and -0.043 sec for the Tehachapi Mountains. Kanamori and Hadley (1975) presented an average velocity profile for southern California. Using their model, the travel time for a 50 km section would be 7.432 sec. Relative to the Kanamori and Hadley model, all of the profiles modeled here would be slow. The residuals for the San Joaquin Valley would be +0.251 sec, +0.143 sec for the Tehachapi Mountains and +0.196 sec for the Mojave Desert. These values suggest an overall slower crust and uppermost mantle for these sections relative to that of Kanamori and Hadley. The thick sediments in the San Joaquin Valley, the root of the range and the low-density granitic rocks and alluvial cover of the Mojave Desert could easily account for the residuals. Many studies have been made of teleseismic P—wave delays in southern California (Kanamori and Hadley, 1975; Raikes, 1976, 1980; Hadley and Kanamori, 1977; Raikes and Hadley, 1979; Walck and Minster, 1982; Hearn, 1984). These studies showed variations of up to 3 sec in residual arrival times. These delays have been attributed to variations in mantle velocity and not to crustal velocity changes. Ergas and Jackson (1981) studied the crustal 137 velocity variations in the southern California and concluded that the variations were on the order of only 1%. Travel time variations among the gravity models presented here were less than 2% and were less than 4% relative to that of Kanamori and Hadley (1975). Although residuals of a few hundreths to a tenth of a second could be measured, and thus better constrain the gravity models, the effects of the mantle velocity heterogeneity would have to be accounted for before the crustal component could be determined. Such an analysis is beyond the scope of this s tudy. H. SUMMARY OF GRAVITY RESULTS The gravity models indicate a thickened crust beneath the Tehachapi Mountains. The crust thickens from 27-30 km under the Mojave Desert and San Joaquin Valley to 35 km under the range. A low-density upper crustal layer extends to about 10 km in both the Mojave Desert and San Joaquin Valley. Within the Tehachapi Mountains, low-density plutons extend to a maximum of only 5 km in the northeastern part of the range near Tehachapi Valley. Thinning southwestward, the plutons are absent southwest of Tejon Canyon. Modeling indicates that the Garlock fault is a major crustal boundary along the length of the Tehachapi Mountains. Low-density plutons are present along the length 138 of the range southeast of the fault but are largely absent to the north. This density contrast across the fault is expressed as a decrease in the gravity and a large gravity gradient. However, because the density contrast extends through much of the crust, the associated gravity anomaly has a wavelength of 10-20 km. The ultimate depth to which the Garlock fault extends can not be constrained by the model, however, the data do suggest that the density contrast, and presumably the fault, extends through the crust into the mantle. The indication that the Garlock fault extends through the crust and some depth into the mantle is supported by the thickness of the crust in the region. The Sierra Nevada — White Mountain batholith has a crustal root extending to a depth of some 40-60 km. Lateral motion within the Basin and Range north of the Garlock fault has transported those ranges 48-64 km westward, relative to the Mojave Desert (Davis and Burchfiel, 1973). Since the Sierra Nevada - White Mountain root has remained with the ranges, it suggests that the entire crust and upper mantle of the Basin and Range moved relative to the Mojave Desert. The White Wolf fault is also modeled as extending through the crust. The fault acts as a boundary between rocks of differing density and the density contrast extends through the crust. Most likely, the fault flattens out at some depth, perhaps in the lowermost crust or upper mantle. 139 The thickness of the root beneath the Tehachapi Mountains is best modeled as being approximately 35 km, a thickening of 4—5 km relative to the adjacent areas. Modeling suggests that the gravity data is mildly sensitive to the crustal thickness. Variations of 0.5-1 km from the modeled value could be acceptable, variations of 5 km, indicating no root (30 km crust) or double the root thickness (40 km crust) are not compatible with the data. One important question to be addressed is the aspect of isostasy. Isostasy can be evaluated in several manners; topographic height versus root thickness; isostatic anomaly calculations and pressure estimates. To estimate the thickness of the crust based on topography, calculations using Archimede's principal were made assuming different crustal densities and a mantle _ 3 density of 3.25 g cm • Assuming a crustal density of 2.67 — 3 g cm , typically used in gravity reduction calculations, the crustal thickness averages between 33.5 and 35 km. However, the density of many of the rocks exposed at the surface (i.e. the tonalites and the met amorphics) have _ 3 densities much higher than 2.67 g cm J and the density probably increases with depth. Assuming a density of 2.74 g _ o cm (the density of the tonalite of Bear Valley Springs) crustal thicknesses average 34 to 36 km. A final crustal _ 3 density of 2.82 g cm (the value for some of metamorphic rocks) indicates an average thickness of 35 to 37 km. These 140 estimates suggest that, based on the modeled crustal thickness of 35 km, the Tehachapi Mountains are in Airy- type isostatic equilibrium. In a manner similar to Hill ( 1978), the pressure for the modeled crustal columns in the Tehachapi Mountains and adjacent San Joaquin Valley and Mojave Desert was calculated to determine the extent of isostatic balance across the region. The calculation used the densities and t h i c k n e s s e s o f t h e l a y e r s d e r i v e d f r o m t h e c r u s t a l m o d e l s . Calculated pressures at the base of the columns at 50 k m r a n g e f r o m 1,444 G P a to 1,470 G P a ( F i g u r e s 26-28), T h e average was 1 , 454 GPa and all columns were within 2% of t h a t a v e r a g e . T h e s e c a l c u l a t i o n s a r e n o t p a r t i c u l a r l y s e n s i t i v e to m i n o r c h a n g e s i n t h e d e n s i t y o r t h i c k n e s s o f a g i v e n l a y e r . V a r i a t i o n s o f a f e w p e r c e n t w i l l n o t p r o d u c e significant changes in the calculated pressures. However, the uniform pressure across the area suggests that, on a regional basis, the Tehachapi Mountains are in isostatic equilibrium. This would represent an Airy-type of isostasy, Roberts e t al, (1981) prepared an isostatic residual anomaly map of California, Their model assumes complete local compensation (Airy-Heiskanen type) with a crust- — 3 mantle density contrast of 0.40 g cm , probably a minimum — 3 value, and a crustal density of 2,67 g cm Isostatic residuals over the Tehachapi Mountains (Figure 30) vary from +20 mgal over Grapevine Canyon to -10 mgal northeast 141 of Tehachapi Valley. Oscillations of the isostatic residuals around zero are indicative of isostatic balance. The strongly negative Bouguer gravity values of the Tehachapi Mountains and Sierra Nevada are not isolated to the batholithic terrane itself. Rather, they are part of a wide area of strongly negative gravity extending across much of the western United States (Figure 10). Eaton e t al . (1978) argue that no single cause can account for the anomalous gravity. They note that gravity values over the Sierra Nevada are similar to those over the Great Basin, yet the crust beneath the Sierra extends to 50-60 km whereas that under the Great Basin extends to only 20-30 km. They suggest that it is a combination of effects (temperature, composition and thickness of the crust and lithosphere) that are responsible for the low gravity. On a regional basis they believe that isostasy is maintained largely through a Pratt rather than an Airy type mechanism. Woollard (1972, and references therein) noted that within North America there is a relationship between isostatic anomalies and crust and mantle velocities. Positive anomalies are associated with a fast mantle whereas negative values are associated with a slow mantle. The Tehachapi Mountains are characterized by positive isostatic anomalies of -10 to +15 mgal (Figure 30) which would suggest a fast mantle. However, numerous studies (Hadley and Kanamori, 1977; Raikes, 1980; Ergas and 142 Jackson, 1981; Walck and Minster, 1982 ; Aki , 1982 ; Humphreys et al., 1984) suggest that the mantle below the Tehachapi Mountains is slow, opposite to the relationship observed by Woollard. Apparently, the isostatic anomalies in the Tehachapi Mountains are strongly influenced by the _ 3 high density (>2.67 g cm ) of crustal rocks rather than by deeper crust—mantle boundary and mantle density effects. The gravity increase from the Sierra Nevada southward into the Tehachapi Mountains can be interpreted as the result of a combination of two effects. First, the decrease in crustal thickness from north to south along the Sierra Nevada axis resulting in a shallowing of the mantle. Second, a southweard increase in metamorphic grade and density of the rocks indicating that deeper levels of the batholithic complex are being exposed. The presence of these high-density rocks at the surface and the decrease in crustal thickness combine to cause an increase in the gravity. Upward continuation of the gravity field indicates that most of the gravity anomalies observed in the Tehachapi Mountains have near—surface sources. Their affects are rapidly attenuated with altitude such that at 2 km only the large amplitude anomalies remain. The principal anomalies, the low over the Antelope Valley and the high of the Tehachapi Mountains persist even to 30 km. The persistence of these regional anomalies to such high levels 143 suggest that they are the result of major crustal structure. In general, anomalies persist to altitudes similar to their dimensions. Small-scale masses affect the gravity field to only a few kilometers whereas crustal-scale anomalies are evident even to continuations above 30 km. The gradient observed in the field above 30 km most likely reflects regional variations in the gravity field resulting from mantle anomalies rather than crustal anomalies. 144 SUMMARY T h e p o t e n t i a l f i e l d ( g r a v i t y a n d m a g n e t i c ) d a t a c o l l e c t e d i n t h e T e h a c h a p i M o u n t a i n s i n d i c a t e t h a t s o m e o f t h e s t r u c t u r e s a n d r o c k b o d i e s e x h i b i t b o t h g r a v i t y a n d m a g n e t i c a n o m a l i e s , s o m e s i n g l e a n o m a l i e s , a n d s o m e n o a n o m a l i e s a t a l l . T h e m a g n e t i c f i e l d o v e r t h e T e h a c h a p i M o u n t a i n s i s r e l a t i v e l y s i m p l e , d e v o i d o f m a n y l a r g e a n o m a l i e s a n d b e i n g c o n t r o l l e d l a r g e l y b y a n o m a l i e s f r o m a r e a s a d j a c e n t t o t h e r a n g e . T h e c r y s t a l l i n e b a s e m e n t ( t o n a l i t e o f B e a r V a l l e y S p r i n g s a n d t h e m e t a m o r p h i c r o c k s ) a p p e a r s t o b e m a g n e t i c a l l y h o m o g e n e o u s . S u s c e p t i b i l i t i e s a n d r e m n a n t m a g n e t i z a t i o n s f o r t h e p l u t o n i c a n d m e t a m o r p h i c r o c k s a r e l o w ( T a b l e I ) . M a g n e t i c a n o m a l i e s w i t h i n r e g i o n s o f c r y s t a l l i n e r o c k a p p e a r t o r e s u l t f r o m m i n o r v a r i a t i o n s i n t h e s u s c e p t i b i l i t y . T h e T e r t i a r y v o l c a n i c a n d c l a s t i c r o c k s a l s o i n d u c e s i g n i f i c a n t a n o m a l i e s b e c a u s e t h e y c o v e r t h e h i g h l y m a g n e t i c g r a n o d i o r i t e o f C l a r a v i l l e r a t h e r t h a n b e c a u s e t h e y a r e t h e m s e l v e s i n t r i n s i c a l l y m a g n e t i c . T h e g r a v i t y d a t a i n d i c a t e t h a t t h e T e h a c h a p i M o u n t a i n s a r e c h a r a c t e r i z e d b y a n o r t h e a s t t r e n d i n g h i g h . P a r t o f t h e a n o m a l y i s p r o d u c e d b y t h e h i g h d e n s i t y o f t h e m e t a m o r p h i c r o c k s i n t h e s o u t h w e s t e r n p a r t o f t h e r a n g e . H o w e v e r , m u c h o f t h e o b s e r v e d g r a v i t y r e l i e f r e s u l t s f r o m t h e 145 j u x t a p o s i t i o n o f t h e t h i c k s e c t i o n s o f l o w — d e n s i t y s e d i m e n t s i n t h e w e s t e r n M o j a v e D e s e r t a n d s o u t h e r n S a n J o a q u i n V a l l e y a g a i n s t h i g h - d e n s i t y p l u t o n i c a n d metamorphic rocks in the range. T h a t p a r t o f t h e g r a v i t y h i g h r e s u l t i n g f r o m h i g h - density hornblende-rich metamorphic rocks extends from the S a n E m i g d i o M o u n t a i n s i n t o t h e s o u t h w e s t e r n T e h a c h a p i Mountains. The anomaly is truncated on the southeast by the Garlock and Pastoria faults and is marked by a large gradient. Because of the large density contrast (up to 0.45 — 3 g cm ) between the metamorphic and surrounding rocks, gravity over the metamorphic terrane stands 18-20 mgal above the adjacent areas. The Garlock and Patoria faults are marked by a large gravity gradient but no magnetic anomaly. These faults juxtapose the high-density mafic metamorphic rocks to the north against low-density granitic plutons to the south. The gradient follows the Garlock fault and then the Pastoria fault, rather than just the Garlock fault. This pattern results from the juxtaposition of the differing rock types across the fault at the surface. Gravity models indicate that the crust beneath the Tehachapi Mountains has a thickness of approximately 35 km, 5-8 km thicker than the adjacent San Joaquin Valley and Mojave Desert. Modeling suggests that the crustal structure of the San Joaquin Valley adjacent to the range is similar 146 to that for the valley farther north. The crustal structure of the Mojave Desert adjacent to the mountains is somewhat different than that for the central Mojave being somewhat less dense though of comparable thickness. Modeling of the Tehachapi Mountain block suggests that it represents an upended section through the Sierra Nevada batholith. At depth the section has been removed along a thrust fault and replaced by a section of Pelona schist and oceanic crust. Archimedes-type calculations, isostatic and pressure calculations all suggest that the range is in isostatic balance with the adjacent San Joaquin Valley and Mojave Desert. This type of isostasy suggests an Airy-type mechanism, though Pratt-type isostasy may play a role deeper in the mantle. Considerable geophysical work could yet be undertaken in the Tehachapi Mountains. More detailed gravity surveys of the valley system having a higher station-density might help resolve the origin of these valleys. Detailed profiles across the metasedimentary pendants both north and south of the Garlock fault would allow modeling of their masses and subsurface shapes. 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Geological Survey Miscellaneous Investigations Map GP-954A. 171 TABLES 172 TABLE 1 ROCK MAGNETIC SUSCEPTIBILITIES ROCK TYPE SUSCEPTIBILITY SOURCE x 10-4 EMU CM-3 PLUTONICS granite of Tejon Lookout granite of Tehachapi Airport granodiorite of Claraville granodiorite of Gato-Montes tonalite of Bear Valley Springs undifferentiated mafic rocks average acidic METAMORPHICS undifferentiated gneiss amphibolite Pelona schist average metamorphic METASEDIMENTS marble (LaLiebre & Bronco Cyn.) slate quartzite s chi st hornfels (La Liebre) METAVOLCANICS greens tones metatuff SEDIMENTS sandstone (Sand Canyon) shale arkose VOLCANICS basalt (Tehachapi Mountains) tuff (Sand Canyon) ande si te rhyolite Tertiary volcanic rocks Ref e rence s: A. This study B. Telford et al. (1976) C. Oliver (1982) 0.03-0.07 A 0.01 A 0.15-12.5 A 0.01-0.02 A 0.19 A 0.18-0.40 A 65 B 0.06-0.45 A 0.6-58 B,C 0.16 D 0-58 B -0.005 - 0.07 A 0.2-5 B,D 3.5 B 0.25-2.4 B 0.08-0.09 A 0.4-4 D 0.1-5 E 0.4-7.5 A 5-15 D 44 C 1.2-2.2 A 0.1-0.5 A 135 B,F 0.2-30 D 8.73-28.65 B,F D. Mooney and Bleifuss (1953) E. Oliver (1972) F. Dobrin (1976) 173 TABLE 2 ROCK DENSITIES ROCK TYPE DENSITY AVERAGE SOURCE RANGE DENSITY (G CM-3) (G CM-3) CRYSTALLINE BASEMENT hornblende—rich diorite to tonalite 2.82+0.05 gabbro to quartz diorite 2.93+0.02 tonalite to quartz diorite 2.80+0.04 tonalite of Bear Valley Springs 2.74+0.04 felsic masses in the tonalite 2.65+0.03 biotite granodiorite of Lebec 2.67+0.02 fine-grained facies 2.63+0.02 felsic marginal facies 2 .62 + 0.02 biotite granodiorite of Gato-Montes 2.67+0.03 biotite granodiorite of Cameron 2.65+0.01 biotite granodiorite of Claraville 2.68+0.03 granite of Tejon Lookout 2.61+0.02 biotite tonalite of Mt. Adelaide 2.70+0.04 granite of Tehachapi Airport 2.59+0.02 pink granite of Bishop Ranch 2.58+0.03 granodiorite of Hoffman Canyon 2.73+0.03 Frazier Mountain gneiss and schist 2.70+0.09 Pelona schist of Tehachapi Mountains 2.80 undifferentiated metamorphic rocks 2.60-3.06 2.78 METASEDIMENATRY ROCKS La Liebre—Bronco Canyon pendants 2.64-2.80 2.7 C La Liebre pendant hornfels 2 .60-2.80 2.7 C Tehcahapi Mt. limestone and dolomite 2.6-2.78 2.70+0.01 B dirty quartzite-graywacke 2.7 1-2.80 2.76 D slate—mica schist 2.30-2.90 2.64 E Goddard Pendant 2.65 F Paleozoics of the Sierra Nevada CM 1 in CM G Mesozoic—Paleozoic pendants 2 . 8 6 + 0.11 G METAVOLCANIC ROCKS biotite-schist hornfels 2.70-3.03 2.78 D gneis s 2.83-2.89 2.86 D chlorite-schist greenstones 2.92-3.14 3.0 1 E Goddard pendant 2.60-2.88 F VOLCANIC ROCKS Western Mojave Desert 1.4 5-2.9 2 2.60 ] Colorado River Area 2.50-2.79 2.68 Channel Islands 1.70-2.80 2.45 Tehachapi Mountain basalts 2.37-2.78 2.59 { tuff, tuff breccia (Sand Canyon) 1.80-2.14 1 .99 i CENOZOIC SEDIMENTS San Joaquin Valley 2.0-2.6 ] 1.85-2.57 Antelope Valley 2.1-2.4 2.25 sandstone (Sand Canyon) 1.7 5-1.99 1. 88 i sand, silt, clay 1.44 ] Ref e rences: A. Ross (1985) B. Oh (1971) C. This study D. Hanna et a1. ( 1974a) E. Oliver and Robbins ( 1982) F. DuBray and Oliver (1981) G. Oliver (1977) H. Mabey (1960) I. Kovach et al. (1962) J. Hanna e t al. ( 1974b) K. Byerly (1966) L. Oliver and Mabey (1963) M. Dobrin (1976) 174 TABLE 3 TEHACHAPI PROFILE CRUSTAL MODEL DENSITIES BODY DENSITY CONTRAST DENSITY ] (G CM"* ) (G CM 3) 1 -0.25 2.42 2 0.10 2.77 3 0.06 2.73 4 0.08 2.75 5 0.28 2.95 6 -0.08 2.59 7 -0.15 2.52 8 0.11 2.78 9 0.11 2.78 10 0.11 2.78 11 0.04 2.71 12 0.085 2.755 13 0.08 2.75 14 0.27 2.94 15 -0.20 2.47 16 -0.02 2.65 17 0.045 2.715 18 0.08 2.75 19 0.28 2.95 20 0.58 3.25 175 1 2 3 4 5 6 7 8 9 10 11 12 13 14 TABLE 4 CANYON PROFILE CRUSTAL MODEL DENSITIES DENSITY_CONTRAST DENSITY (G CM ) (G CM ) -0.3 2.37 0.035 2.705 0.08 2.75 0.275 2.945 0.05 2.72 0.09 2.76 0.08 2.75 0.22 2.89 “0.27 2.40 “0.045 2.625 0.007 2.679 0.08 2.75 0.26 2.93 0.58 3.25 176 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 TABLE 5 PASTORIA CANTON CRUSTAL MODEL DENSITIES DENSITY CONTRAST (G CM 3) -0 .25 0. 1 5 0.08 0.28 -0 .275 0.06 0.00 0.075 0.08 0.25 0.03 0.05 0.08 0.22 -0 .01 0.045 0.20 0.58 ILLUSTRATIONS ILLUSTRATIONS Fi gu r e Figure Fi gu r e Fi gu r e Fi gure Figure Figur e Figure Figure Fi gur e Figure Figure Figure 1. Geography of the Tehachapi Mountains. 2. Geologic map of the Tehachapi Mountains. 3. Aeromagnetic map of the Tehachapi Mountains and adjacent areas. 4. Geologic map of the Cummings Valley area showing location of magnetic profiles. 5. Magnetic profile data for the Cummings Valley area. 6. Geologic map and aeromagnetic profiles over the Tehachapi-Brite Valley area. 7. Geologic map and aeromagnetic profile over the La Liebre pendant. 8. Map of gravity stations. 9. Bouguer gravity map of the Tehachapi Mountains and adjacent areas. 10. Bouguer gravity map of California-Nevada region. 11. Band-pass filtered Bouguer gravity map of the Tehachapi Mountains. 12. Bouguer gravity map of the southwestern Tehachapi Mountains. 13. Band-pass filetered Bouguer gravity map of the southwestern Tehachapi Mountains. 179 Figure Figure Figure Figure Figure F igur e Figure Figure Figure Figure Fi gure Figure Fi gu r e Figure 14. Complete Bouguer gravity map of the Bear Valley-Cummings Valley region. 15. Complete Bouguer gravity map of the Brite Valley-Tehachapi Valley region. 16. First vertical derivative of the Bouguer gravity field. 17. Second vertical derivative of the Bouguer gravity field. 18. Upward continuation of Bouguer gravity field to 1 km. 19. Upward continuation of Bouguer gravity field to 2 km. 20. Upward continuation of Bouguer gravity field to 5 km. 21. Upward continuation of Bouguer gravity field to 10 km. 22. Upward continuation of Bouguer gravity field to 3 0 km. 23. Tehachapi profile crustal model. 24. Tejon Canyon profile crustal model. 25. Pastoria Canyon profile crustal model. 26. Schematic crustal columns for the Mojave Desert. 27. Schematic crustal columns for the San Joaquin V alley. 180 Figure Figure F igu r e 28. Schematic crustal columns for the Tehachapi Mount ains. 29. Schematic geologic cross section of the crust along the Tejon Canyon profile. 30. Isostatic anomaly map of the Tehachapi Mount ains. 181 r1GURE 1. Geography of the Tehachapi Mountains. Shaded regions indicate bedrock exposures. Heavy black lines denote major faults. IN, IS: Pardee —Pas toria transmission line gravity profile, 2: Antelope-Magunden transmission line gravity profile, 3: Bear Mountain Boulevard gravity profile, 4: Mojave Bakersfield highway gravity profile, 5: Tehachapi-Wil1ow Springs Road gravity profile, EF: Edison fault, P.H.F.: Pinon Hill fault, L.O.C.F.: Little Oak Canyon fault, C.F.: Cottonwood fault, T.H.C.F.: Tylerhorse Canyon fault, BM: Bear Mountain, BRV: Bear Valley, BV : Brite Valley, CM: Cummings Mountain, CP: Cache Peak, O.C.C.: Oak Creek Canyon, SM: Soledad Mountain, RH : Rosamond Hills, B.T.C.: Bear Trap Canyon. 182 FIGURE 2. Geologic map of the Tehachapi Adapted from Ross (1980). Mount ains. 184 • ' ' M . > . > i « >&*$&m&5r-»- “ “mm ui ii, ‘ , M l S0Z0IC-PALI0Z04C MCTAMOftfNKC J5*<r nrw nr45' 00 cn FIGURE 3. Aeromagnetic map of the Tehachapi Mountains and adjacent areas. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Countour interval equals 20 gammas. 186 1 nr i i a f a o nr 1 0 5 10 15 20 2b MILE? 1 0 10 20 30 40 KILOMETERS CONTOUR INTERVAL 20 GAMMA 187 FIGURE 4. Geologic map of the Cummings Valley area showing location of magnetic profiles. Heavy solid lines labeled A-I denote the locations of surface magnetic profiles. Heavy solid lines labeled 1 and 2 denote the locations of aeromagnetic profiles. Fine solid and dashed lines denote faults. Geologic units: Kbv: tonalite of Bear Valley Springs, MzPz: metasedimentary pendants, Q: alluvium. 188 189 35°iO* N ■ 1>>.V||, .:, > ■ *•» / ,M 4if K t i v: : V ; 35V N 118°40' 118°35' 118°30' FIGURE 5. Magnetic profile data for Cummings Valley area# Upper panels illustrate surface profiles, lines A-I. Lower panels illustrate aeromagnetic profiles, profiles 1 and 2. Letters on the profiles denote features discussed in the text. Dashed lines on surface profile diagrams indicate bends in the prof iles. 190 *Z£o8II ,S€ .6C.WI G AM M AS 8 £ G AM M AS 3 *3 50 O * T 1 r rn M oo PO 00 VJ1 UD AEROMAGNETIC PROFILES G AM M AS 8 G AM M AS « z 8 o z m x z t f ) m SURFACE PROFILES FIGURE 6. Geologic map and aeromagnetic profiles over the j Tehachapi - Brite Valley area. Lower panel is ! the geologic map. Profile locations are indicated by heavy solid lines. Upper panels are the aeromagnetic profiles. Letters on the profiles denote features discussed in the | text. Fine solid and dashed lines indicate faults. Geologic units: Kbv: tonalite of Bear Valley Springs, MzPz: metasedimentary pendants, j Q: alluvium. S V W W V J SVWWV9 A E R O M A G N E T IC P R O F IL E S 60 40 20 PROFILE 2 0 60 40 PRO FILE 1 C 33' 37* 32' 3!' 29 ‘ 28* PROFILE 2 M7P7 JJ8*35 1 ii2 j 1 Ml I 0 1/2 1 KM 193 FIGURE 7. Geologic map and aeromagnetic profile over the La Liebre pendant. Lower panel is the geologic map. Heavy solid line labeled FL indicates flight line location. Upper panel depicts ; aeromagnetic profile. Geologic units: Ktl: j i granite of Tejon Lookout, Kg: granodiorite of j Gato-Montes, Kle: granodiorite of Lebec, Jb: metasediments (lined area: marble, cross- i hatched area: hornfels), Kgh: undivided metamorphic rocks. 194 0 AMMAA o ; F I G U R E 8. M a p of d e n o t e d gra v i t y stations. Each b y a d o t . s tat ion 197 3 5.375° 34.65 o 118.10 FIGURE 9. B o u g u e r g r a v i t y m a p of t h e T e h a c h a p i M o u n t a i n s a n d a d j a c e n t a r e a s . S h a d e d r e g i o n s i n d i c a t e b e d r o c k o u t c r o p . H e a v y s o l i d l i n e s d e n o t e m a j o r f a u l t s . L e t t e r s r e f e r t o f e a t u r e s d i s c u s s e d i n t h e t e x t . C o n t o u r i n t e r v a l e q u a l s 2 m g a 1. 198 35 * 15 35* 00 * 34 * 45 ' 118* 45 * 118* 30 ' 1 18‘ 15' 139 FIGURE 10. Bouguer gravity map of the Califoria-Nevada region. Shaded regions indicate exposures of batholithic rocks. Contour interval equals 50 mgal. 200 200 250 2 0C 10C 100 KM «• 118° 38 35 201 ___1 FIGURE 11. Band-pass filtered Bouguer gravity map of the Tehachapi Mountains. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mga1. 202 35* I 5' j — 35* 00' hr 34* 45’ © 118*45* 118° 30' 118* 15* 203 FIGURE 12. Bouguer gravity map of the southwestern Tehachapi Mountains. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mga1. 204 3S-€0Q' 34*45' 118®4S' 118* 30‘ 205 ___i FIGURE 13. Band-pass filtered Bouguer gravity map of the southwestern Tehachapi Mountains. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mgal. 206 10 20 10 10 20 30, 34°4S* 116"30 207 FIGURE 14. Complete Bouguer gravity map of the Bear Valley - Cummings Valley region. Shaded regions indicate bedrock outcrop. Dots indicate gravity stations. LBV: Lower Bear Valley, MBV: Middle Bear Valley, UBV : Upper Bear Valley, CV : Cummings Valley, BV: Brite Valley. Letters A-J refer to features discussed in the text. Contour interval equals 1 mgal. 208 35° 10' 35° 7.5' L COMPLETE BOUGUER G R A V IT Y MAP O F BEAR V A L L E Y - C U M M IN G S V A L L E Y REGIO N 118° 40' 118° 37.5' 118° 35' ; . w y : L B V ! 2 MILES 1 2 KIL0ME7FRS 209 FIGURE 15. Complete Bouguer gravity map of the Brite Valley - Western Tehachapi Valley region. Shaded regions indicate bedrock outcrop. Dots indicate gravity stations. BV: Brite Valley, TV: Tehachapi Valley. Letters J-N refer to features discussed in the text. Contour interval equals 1 mgal. 210 COMPLETE BOUGUER G R A VITY MAP OF BRITE VALLEY - WESTERN 7 EHACHAI’ I VALLEY REGION 3b° 10‘ 3b° 7.b' 118° 32 b 118° 30' 1 1 8 ° ? 7 . h ' 1 1 8 ° 118° 22.5' S i S i - S ' A W i v S ? . ' m M m m m • : & S 8 * 3 S 11® •XjXvXvXvXv* TECHACHAP 8 w > m« c < w M s v > . v . v . ■ . v y . y . v . O l l f \ > ■ m m ■ I - X - X v X v X v . ; ' ; . : . : . : ^ - . 1 2 MILES 1 2 KILOMETERS FIGURE 16. First vertical derivative of the Bouguer gravity field. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 0.5 mgal km ^ . 212 FIRST V E R T IC A L D E R IV A T IV E FIGURE 17. Second vertical derivative of the Bouguer gravity field. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major _ 2 faults. Contour interval equals 0.5 mgal km 214 — SECOND VE R TIC A L D E R IV A TIV E FIGURE 18. Upward c o n t i n u a t i o n of the B ouguer gravity field to 1 km. Shaded regions indicate b e d r o c k outcrop. Heavy solid lines denote m a jor faults. Letters refer to features discussed in the text. Contour interval equals 2 mgal. 216 r 1 KM 35” 35” 34° 217 FIGURE 19. Upward c o n t i n u a t i o n of the Bouguer grav ity field to 2 km. Shaded regions indicate b e d r o c k outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mgal. 218 35* 15' 35“ 00' 2 K 34* 45' % 1 18*45' 13 8* 30' 118° 15' 219 FIGURE 20. Upward c o n t i n u a t i o n of the Bou g u e r gravity field to 5 km. Shaded regions indicate b e d r o c k outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mgal. 220 —1 5 K 3 5‘ 15 15 35° 00 15 15 34“ 45 I : 8* 3C 1 18e 1 5 1 18r 45 2 2 1 FIGURE 21. Upward continuation of the Bouguer gravity field to 10 km. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mga1. 222 70 KM FIGURE 22. Upward continuation of the Bouguer gravity field to 30 km. Shaded regions indicate bedrock outcrop. Heavy solid lines denote major faults. Letters refer to features discussed in the text. Contour interval equals 2 mgal. 224 30 . < • ’' s < •,, 'jj 1 Ok m 225 FIGURE 23. Tehachapi profile crustal model. Upper panel displays observed and modeled gravity profiles. Lower panel displays crustal section. Letters on profiles refer to features discussed in the text. In lower panel, W: White Wolf fault, G: Garlock fault, M: Moho. Numbers in lower panel refer to crustal bodies, the densities of which are listed in Table 3. 226 -50 f EHACHAPI PROFILE CRUSTAL MODEL 150 0 ***** 1 \ h i i i i i i i 1 1 1 1 i i i i i i 1 1 in i i i m i i i i 1 1 1 1 1 1 i 1 1 i i i i i i h i i i i 1 1 m i i 1 1 i i i i 1 1 i m 40 7 D tO T 4 » 0 B _ 12 16 17 18 13 19 14 20 ro r v > " s i FIGURE 24. Tejon Canyon profile crustal model. Upper panel displays observed and modeled gravity profiles. Lower panel displays crustal section. Letters on profiles refer to features discussed in the text. In lower panel, W: White Wolf fault, G: Garlock fault, M: Moho. Numbers in lower panel refer to crustal bodies, the densities of which are listed in Table 4. 228 TEJON CANYON PROFILE CRUSTAL MODEL 50 150 0 £ 10 1 1 12 s s 13 14 50 ro ro <£> FIGURE 25. Pastoria Canyon profile crustal model. Upper panel displays observed and modeled gravity profiles. Lower panel displays crustal section. In the lower panel, W: White Wolf fault, G: Garlock fault, S: San Andreas fault, M: Moho. Numbers in lower panel refer to crustal bodies, the densities of which are listed in Table 5. 230 PASTORIA CANYON PROFILE CRUSTAL MODEL 50 -150 0 15 1 1 12 16 10 17 14 18 50 ro co FIGURE 26. Schematic crustal columns for the Mojave Desert. Numbers in columns indicate density of — Q the crust in g cm . 232 233 depth in kilometers c n w to O O O O so M CO W C SO M ► ►4 c n O 's....... s .... to t o “ n r" to i — * M ( 0 •s j b > / ] c n c n c n c n c n / TEHACHAPI PROFILE > CO to to to to i to TEJON CANYON > M ^ ....... - “.... CO CO • s j c n O i •o c n to ...A . I £ PROFILE 5 ------------------« ................ C O to to > to O 0 0 0 > c n O o c n 0 SEISMIC REFRACTION CENTRAL MOJAVE to 0> 00 F 8 ^ t-l < M f o o M H * *0 so O » — 4 t " 1 H MOJAVE DESERT MODELS FIGURE 27. Schematic crustal columns for the San Joaquin Valley. Numbers in columns indicate density of _ Q the crust in g cm . 234 PRESSURE A T 5 0 KILOMETERS DEPTH IN KILOMETERS 01 * co to o o o o S T ................. ........■■■«------ to to to / X to < 0 •O / ? 0 1 O l c o /. M TEHACHAPI * PROFILE I £ 0 >— tj » CO k> c n to 01 TT sj o J£L w TEJON CANYON PROFILE > ....... » ... to to to to 8 (0 0 1 •o 0 1 0 0 to t PASTORIA CANYON PROFILE \ J* 0) to to to w o 0 6 K j c o O o o o o SEISMIC REFRACTION SAN JOAQUIN VALLEY * . » ~ o p M ro oo on S A N JOAQUIN VALLEY MODELS FIGURE 28. Schematic crustal columns for the Tehachapi Mountains. Numbers in columns indicate density — Q of the crust in g cm . 236 237 DEPTH IN KILOMETERS w O TEHACHAPI PROFILE * T > ta w CA CA c M > H c n O I T) • 4» <0 5 3.25 2.92 2.75 2.745 ^ w to to to to S to 0 0 K l • o • o S 0 5 < 0 c n to o W' g 4 k . y to ? to < 0) to *--------- to to to b o •o O ) c n •o K l TEJON CANYON PROFILE PASTORIA CANYON PROFILE SEISMIC REFRACTION SIERRA NEVADA to O O TEHACHAPI MOUNTAIN MODELS FIGURE 29. Schematic geologic cross section of the crust along the Tejon Canyon profile. QE: sediments of the San Joaquin Valley, MPb: undifferen tiated Mesozoic and Paleozoic basement, my: mylonite, sc: Pelona schist and correlative rock units, oc: oceanic crust, Ct: Cretaceous tonalite of Bear Valley Springs, um: undiffer entiated metamorphic rocks, al : alluvium, Cg: Cretaceous granitic rocks, WW: White Wolf thrust fault, N.G.F.: north branch of the Garlock fault, S.G.F.: south branch of the Garlock fault, S.H.T.: Sand Hills thrust fault, RT: Rand thrust fault, CRT: Coast Range thrust f au11. 238 DEPTH I N KILOMETERS MOJAVE DESERT TECHACHAPI MOUNTIANS SAN JOAQUIN VALLEY um MPb sc rtiy CRT- sc sc sc sc sc 20 < QC; OC oc; 30 MOHO MANTLE 40 10 15 20 25 30 km 0 5 No vertical exaggeration r\3 co LO FIGURE 30.Isostatic anomaly map of the Tehachapi Mountains. Shaded regions indicate bedrock outcrop. Contour interval equals 5 mgal. 240 3 5 ' 1 3 C I ' N n APPENDICES 242 APPENDIX I. GRAVITY DATA. APPENDIX I GRAVITY DATA The gravity data is listed one station per line. Columns 1-15: Station name and number. Columns 16-30: U.S.G.S. topographic map sheet on which the station was located. Columns 31-38: Station latitude in degrees North. Columns 39-47: Station longitude in degrees West. Columns 48-54: Elevation in feet above sea level. Columns 55-65: Absolute observed gravity in mgal. Columns 66-71: Topographic correction in mgal. Columns 72-79: Complete Bouguer gravity in mgal. Column 80: Station elevation source. A. California Water Resources Agency. B. Measured during study (see Appendix II). C. Bear Valley Community Services District. D. Southern California Edison Company. E. U.S.G.S. topographic map sheets (spot elevat ions). F. U.S.G.S. topographic map sheet (road intersections). G. U.S.G.S. or N.G.S. benchmarks. H. Tehachapi Cummings Water District (wells). I. 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( - k . k. U u U u u u u u U u u u u u u u U u U u u u u u U U u u u u u u u NI • • • m • m m c e c c c C C * * m « m < n n m n 41 m m < <• m m < m * • m m m < n m m n n m m n m « r4 r* *4 v# M -r4 «* > > > > > > > t . 1 - t- t - u •- (- t - t - (- k- t - u k- t - k- u k- k- k- k- t- l k- k- k- k- k- w k> k. k. k> k- • • • • m • 41 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 O 0 0 0 0 0 0 0 0 0 O u u u u NI u u NI NI u u u u NI NI NI u c c c Ok a a a . a b a.44 4 > 4* 4 * 4« 44 44 44 44 44 4« 44 44 44 44 44 44 44 44 4» 44 44 44 44 44 44 44 44 44 44 44 44 44 44 • • • • • • • • • • • • • • • • • •Vt * * * • 41 * * r m <4 W > <* 41 <4 <4 m 14 14 m 14 14 14 m M 14 * • t 14 41 14 14 M 14 14 14 Mt 14 14 14 14 m fQ JO JO 43 J 3 <0 43 4 3 jO 43 jO 43 43 jO 43 43 4 3 > > > t- t k- L- k- i - t- * * m m < 41 m m « 41 m < « <« m 41 <• m <* 41 « « « m • f m < 9 <0 m < m m % m m • • • • m m • • • • » m m t t k . ( - k- a» a t a t a t a t m at O l a . a a . a . a . a . a . CL CL a . a CL a a . 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CL CL CL *— t r * v t *4 v t •— t m ■a m ■0 m X I u u u U O u u U U u U u U W u U U U u W U U u U U u U U u u u NI U O U NI NI u U NI u u N I u N I u > 43 > r t > 4 3 u u u u u u u U u u u u u u u u U U u U u u u u u u a u u LJ u u u u u u U u u u u NI u U u U U N IN IN IN I u N IN IN I U u 4* *» 4* u u u u u u u u u u u u <« < « m m <« < < 4 m n « m m m m m n m m m m m m m m m * m m m m m m m m m m m m • C a L O C\J 44*4*44***** „ 3 3 3 3 3 3 3 3 3 3 3 3 tfor^{<^«ro,tftf^er'tferep'o‘o'«r‘«rcr(rtftftfo’o’(rtfiro'</o’^tfo,«i'«/tfo'o'tfrfo't/o'«rir^ 4 4 orcr«rorarcrBrcr»,Bro,ar************************************0****,*<**JJ»* * « * * * « * m * * * nNo^<»)^,n,orNOOO*0^ftft«»4)rNcpO'Q~ftft*-m3 43fNa|0'Q«'«ftft*,m32§rNapoo»«ftft *u 04 b • r ait bvd rvin 33 2092 03 b • r ait b v* rvln 33 2093 06 be r at b vd rvin 33 2093 08 b a r at b vd rvin 33 2093 09 b • r at b vd rvin 33 2094 10 b • r at bvd rvin 33 2094 11 b • r at bvd rvin 33 2095 12 b • r at bvd rvin 35 2095 13 b • r at bvd aer eioun e n 33 2096 14 be r at bvd aer aoun e n 33. 2097 16 be r at b vd aer •oun e n 33 2137 17 b • r at b vd aer •cun e n 35 2148 18 b a r at bvd aer •oun e n 33 2164 19 b • r at b vd aer noun e n 33 2183 20 b • r at b vd aer •oun e n 35 2194 21 b • r at b vd aer • oun e n 35 2203 22 be r at bvd aer •oun e n 35 2220 23 be r at b vd aer •oun e n 33. 2230 24 be r at bvd aer •oun e n 33 2284 23 be r at bvd aer •oun e n 35 2316 26 be r at bvd aer •oun e n 33. 2344 27 be r at bvd aer aoun e n 35 2364 28 be r at bvd aer •oun e n 33 2371 30 b e r at bvd aer •oun e n 33 2414 33 be r at bvd aer •oun e n 35 2332 36 b e r at bvd aer •oun e n 33 2559 37 b e r at bvd aer moun e n 33 2588 38 b« celtr en aer •oun e n 35 2617 01 b e r velley aer •oun e n 33 2056 02 b e r ve1 lay aer • oun e n 35 2050 03 b e r vellay aer •oun e n 35 2111 04 b e r ve11 ay aer •oun e n 35. 2035 03 be r veHay aer •oun e n 33. 2046 06 b e r ve1 lay aer moun e n 35. 2030 07 b e r veHay aer • oun e n 33 1999 10 b e r veHay aer moun e n 35 1971 11 b e r veHay aer •oun e n 35 1973 13 b e r veHay aer moun e n 35 1937 14 be r vellay aer •oun e n 35. 1965 16 b e r vellay aer •oun e n 35. 2051 17 b e r vellay aer •oun e n 33 2083 18 b e r vellay aer •oun e n 33 2022 19 be r vellay aer moun e n 33 1983 20 b e r ve1 lay aer •oun e n 33 2036 21 be r vellay aer • oun e n 35 2104 22 b e r veHay aer • oun e n 35. 2007 23 b e r vellay aer •oun e n 35. 1980 24 b e r vellay aer • oun e n 35. 1981 25 b e r ve1 lay aer aoun e n 35 1977 26 b e r ve1 lay aer •oun e n 33. 1930 27 b e r vellay aer moun e n 33. 1926 28 b e r ve1 lay aer •oun e n 35 1953 29 b e r vellay aer moun e n 33. 1944 30 b e r vellay aer •oun e n 35. 1889 31 b e r ve1 lay aer •oun e n 33 1877 33 b e r vellay aer moun e n 33. 1849 34 be r vellay ter •oun e n 35. 1820 35 be r vellay aer •oun e n 35. 1815 36 b e r vellay aer • oun e n 33. 1740 37 be r veHay aer •oun e n 35. 1713 38 be r veHay aer moun e n 35 1687 7872 467 8 979634 26 04 JO -077 06 B 7827 478 4 979633 18 04 23 -077.39 B 7784 489 4 979631. 68 04.41 -077 32 B 7694 332 2 979649 20 04 72 -077 68 B 7630 342 9 979648 76 OS 18 -077 02 B 7606 333 9 979648 60 05 33 -076. 18 B 7362 363 9 979648. 79 03. 86 -073 07 B 7517 388 2 979647. 85 06 28 -074. 14 B 7471 653. 9 979643 67 06 90 -073 89 B 7428 720 4 979639. 16 07. 47 -073. 78 B 7357 866. 8 979631. 03 07 64 -073. 34 B 7313 937 3 979627. 16 07.87 -072.89 B 7274 1011 3 979623 76 07 95 -071. 92 B 7233 1094. 3 979619 27 08 38 -071. 19 B 7107 1167.7 979614.77 08 47 -071.33 B 7138 1246.7 979609.40 09 27 -071.27 B 7094 1319. 4 979604. 13 10. OO -071 38 B 7070 1421 8 979598.55 09.84 -071.31 B 7046 1503 8 979594 26 09. 50 -071. 33 B 7022 1585.9 979590.30 08 81 -071.36 B 6992 1664 2 979586. 31 07. 68 -072 05 B 6937 1744. 0 979382. 94 08 23 -070. 47 B 6911 1824. 3 979579. 42 07. 92 -069. 37 B 6840 2002. 7 979372. 20 06. 91 -067. 32 B 6673 1990 3 979568 03 06 33 -074. 01 B 6642 1965 0 979368 90 06. 07 -075. 14 B 6615 1919.3 979571.95 05.89 -075.24 B 6588 1835. I 979575. 96 06. 01 -075. 19 B 6633 5782. 3 979319. 60 20. 19 -077. 91 C 6636 5797. 7 979318. 38 20. 71 -077. 64 C 6614 5956 4 979304. 68 24. 79 -078. 27 C 6640 3750. 9 979323. 03 19. 63 -076. 89 C 6616 5645 8 979331. 35 18. 43 -076. 00 C 6578 5664.5 979331.39 16.69 -076.24 C 6620 5468. 3 979343. 34 18. 03 -074. 43 C 6588 5438. 3 979346. 88 16. 73 -073. 95 C 6540 3624. 3 979334. 98 14. 35 -077. 12 C 6453 5730 5 979328. 71 14. 89 -076. 19 C 6495 3780. 1 979324. 77 14. 68 -077. 61 C 6373 5812.2 979321.11 17.69 -077 06 C 6676 5709 0 979320. 35 23. 17 -078 80 C 6712 3332.9 979333.23 19.39 -078 33 C 6743 3177.6 979358.48 16.28 -078.50 C 6792 4827. 3 979379. 15 18. 00 -077. 52 C 6797 4303. 2 979412. 36 18. 18 -073. 86 C 6836 4340.2 979398.11 13.63 -077.86 C 6824 4349. 6 979398. 26 14. 90 -077. 64 C 6862 4417.8 979405.81 14.27 -078.62 C 6888 4271.3 979414.31 14.51 -078.40 C 6879 4226. 4 979418. 58 13. 43 -077. 87 C 6867 4163.3 979421.90 14.49 -077.05 C 6694 5107. 0 979364. 65 13. 88 -076. 71 C 6644 4866. O 979383. 33 13. 68 -074. 57 C 6653 4031. 5 979384. 37 13. 06 -075. 55 C 6376 3199. 9 979363. 42 12. 20 -073. 41 C 6482 4873. 3 979384. 79 09. 85 -073. 58 C 6434 4689. 1 979397. 60 07. 63 -075. 87 C 6488 4666. 4 979398. 95 07. 95 -075. 32 C 6479 4203. 3 979428. 38 03. 04 -075. 92 C 6468 4134. 8 979432. 78 04. 48 -076. 10 C 6486 4078. 6 979436. 93 07. 43 -072. 10 C 18 18. 18 18 18 18 18 18 18 18 18. 18 18 18 18 18. 18 18 18 18 18 18 18 18 18 18. 18 18. 18. 18. 18 18. 2 8. 18 18. 18 18 18 18 18 18 18 18. 18 18 18. 18 18 18. 18 18 18. 18. 18 18. 18. 18 18. 18. 18 18 246 39 baar va lav kaar mountain 33 1697 40 k aar va lav kaana 35 1473 41 kaar va lav k aana 35 1497 42 kear va lav kaana 35 1313 43 bear va lav k aana 33 1503 44 ktar va lav kaana 35 1477 43 kaar va lav kaana 35 1525 46 kcar va lav k aana 33 1343 48 baar va lav kaana 35 1627 49 bear va lav baar mountain 35 1572 50 kaar va lav kaar mountain 33 1558 52 kaar va lav baar mountain 35 1522 53 kaar va lav kaar mountain 33 1509 34 kaar va lav baar mountain 35 1509 55 kaar va lav kaar mountain 33 1481 56 kaar va lav baar mountain 35. 1450 57 kaar va lav kaar mountain 33 1431 58 k aar va lav baar mountain 35. 1464 59 kaar va lav kaar mountain 35 1402 60 kaar va lav baar mountain 35 1408 61 kaar va lav baar mountain 35 1431 62 kaar va lav baar mountain 35. 1404 63 kaar va lay baar mountain 35 1371 100b aar va lay baar mountain 33 1810 101b aar va lay baar mountain 35. 1840 102b aar va lav baar mountain 33 1835 103b aar va 1 ay baar mountain 35 1888 104b aar va lay kaana 35 1890 103b aar va lay k a ana 33 1933 106b aar va lay kaana 35. 1943 107b aar va lav kaana 35. 1897 108b aar va lay kaana 35. 1930 109b aar va lay kaana 35 1887 1lObaar va lay k aana 35 1849 11lbaar va lay k aana 35 1823 112b aar va lay kaana 35 1757 113baar va lay kaana 35 1794 114b®ar va lay k aana 35 1716 113b aar va lay kaana 35. 1680 118b aar va lay k aana 35. 1621 119baar va lay k aana 35. 1610 120b aar va lay k aana 35 1607 121baar va lay kaana 35. 1614 122b aar va lay kaana 33. 1378 123b aar va lay k aana 35. 1392 124baar va lay kaana 35. 1622 123b aar va lay kaana 33. 1646 126baar va lay kaana 35. 1603 127baar va lay kaana 33 1705 128b aar va lay kaana 33 1710 129b aar va lay k aana 35 1737 130baar va lay kaana 35 1749 131b aar va lay baar mountain 35 1323 132b aar va lay baar moun ta in 35 1560 133b aar va lay baar mountain 35 1623 134baar va lay baar mountain 35 1657 135baar va lay baar mountain 35 1584 136 b aar va lay baar mountain 35 1536 137baar va lay baar mountain 35. 1328 138b aar va lay baar mountain 33 1473 139b aar va lay baar mountain 35 1399 6329 4094 8 979435 83 04 42 -075 32 C 3765 4215 3 979424 93 04 33 -077 23 C 5805 4281 3 979420 90 03 40 -076 46 C 5840 4366 8 979416 44 03 22 -076 12 C 3868 4410 2 979413 32 04 33 -075.47 C 5846 4491 2 979409 63 03 23 -073 17 C 5892 4436 7 979412. 46 04 11 -073. 93 C 5933 4683 0 979403 00 03 82 -072 32 C 3931 4390 2 979402 37 03 22 -077 60 C 6468 4088 8 979436. 06 04 45 -074 38 C 6533 4066 7 979437 32 03. 87 -074 71 C 6528 4136 9 979432 44 03 67 -073 48 C 6382 4126 1 979433 28 04 90 -073 95 C 6607 4119 6 979433 44 04 59 -074 49 C 6612 4245 5 979423. 72 03. 67 -073 33 C 6603 4450. 0 979412 30 07. 22 -072 75 C 6566 4852. 0 979387. 27 07. 66 -073 13 C 6362 4574 7 979404. 96 06 34 -073. 63 C 6309 3114 7 979370 20 08.34 -073.36 C 6476 3180 0 979366 38 08 04 -073. 83 C 6454 5108 6 979369 94 09. 42 -073. 53 C 6457 5260. 3 979360. 36 08. 78 -074. 27 C 6446 3166 2 979366 48 08. 36 -073. 92 C 6390 4959. 6 979379. 01 10 02 -073 81 C 6405 4954 5 979379. 66 09. 79 -075 95 C 6316 5317.0 979353.43 11.65 -076 60 C 6272 5789 8 979324. 25 13. 98 -077. 60 C 6159 6119.8 979301 36 14.91 -079 82 C 6222 6265 9 979291.23 15. 86 -080 60 C 6141 6204 2 979294.94 13.09 -081.45 C 6085 6013. 1 979308 03 13. 18 -079.32 C 6074 5992 1 979307. 12 17. 43 -079. 52 C 6043 3948 4 979310 50 15.48 -080.34 C 5958 5563. 9 979334. 72 14. 61 -079. 69 C 5984 5620 3 979334.09 11.86 -079.46 C 3948 5467. 9 979345. 35 09. 39 -079. 23 C 5918 5536.2 979338.74 11.20 -090.27 C 6312 4212 0 979426 83 05.27 -076.65 C 6266 4188. 5 979428. 98 04. 76 -076. 12 C 6187 4167.3 979430.90 03 63 -076 09 C 6168 4224. 1 979427. 56 03. 84 -075. 73 C 6200 4143. 3 979432. 48 03. 25 -076. 08 C 6094 4638. 1 979401 32 05. 25 -075. 84 C 6030 4628. 4 979402 48 04. 14 -076.06 C 3991 4322 0 979408 96 03. 93 -076. 27 C 6057 4459. 0 979412. 40 03. 94 -076. 85 C 6010 4302. 7 979408. 90 04. 29 -077. 58 C 3984 4514 1 979409.04 03. 90 -076.79 C 6055 4347.0 979404.97 06.27 -077.39 C 6084 4318. 7 979407. 16 04. 91 -078 30 C 6068 4766. 7 979391. 28 07. 22 -077. 26 C 6096 4632. 1 979398 78 07. 66 -077 47 C 6334 4144. 1 979433.24 04.64 -073.29 C 6337 4182 5 979431. 43 03 77 -073. 99 C 6371 4087. 2 979436. 70 03. 75 -074. 97 C 6363 4120 9 979434 12 03. 68 -075. 90 C 6332 4109. 7 979435. 90 03. 43 -074. 42 C 6292 4146. 1 979433. 66 03. 50 -074. 00 C 6426 4430 3 979413. 50 05. 45 -073. 16 C 6296 4341.7 979408 30 05.87 -072.81 C 6292 3072. 3 979373. 38 08 09 -073. 14 C 8 8. 8 8 8 . 8 8. 8. a 8. 9 e e 8 8 8 8. 8 8. 8 8 8. 8. 8 8. 8 8 8 8 8 8 8 8. 8. 8. 8 . 8 8. 8. 8. 8 8 8 8. 8. 8. 8. 8 8 8 8. 8. 8. 8. 8 8 8 8. 8. 8. 8 247 140b aar va 1 •V baar Mountain 35 1351 18 6350 5129 9 979369 87 08 43 -072. 46 C 141 bear va 1 •V kaana 35 1337 18 6229 4573 7 979405 77 06 33 -071 81 C 142b car va 1 •Y k aana 33 1384 18 6206 4819 9 979390 50 06. 34 -072 76 C 143b aar va 1 •Y k aana 33 1395 18 6097 4753 7 979391 44 06 22 -075. 98 c 143b aar va 1 • Y k aana 33 1452 18 4002 4680 1 979399 42 04 78 -074 32 c 146baar va 1 •Y kaana 35 1494 18 5925 4743 4 979394 57 05 51 -075 01 c 147b aar va 1 •V k aana 33 1444 18 5939 4467 0 979413 07 03 85 -074 45 c 149b aar va 1 •V k aana 33 1479 18 6229 4165 3 979431 92 03 92 -073 69 c 130baar va 1 •V k aana 33 1442 18 6159 4169 3 979431 63 03. 33 -074 19 c 131b.ar va 1 •V kaana 33 1504 18 6077 4192 4 979429 95 03 14 -075 05 c 132baar va 1 *Y kaana 35 1545 18 6143 4170 5 979430. 96 03 22 -075 78 c 134baar va 1 •Y k aana 35 1495 18 5928 5286 8 979357 87 08 44 -077. 98 c 133b aar va 1 •Y k aana 35 1415 18 5778 5791 2 979319 17 14. 40 -079. 86 c 134b aar va I •Y k aana 35 1759 18 5874 5536 9 979339. 15 10 54 -080 17 c 137baar va 1 • Y k aana 35 1432 18 6566 4417 5 979414 79 04 57 -074 70 c 139baar va I kaana 35 1715 18 6159 4456 5 979411 04 05 07 -078 01 c 160b aar va 1 •Y kaana 35 1704 18 6196 4481 4 979410. 40 05 72 -076 44 c 141b aar va 1 •V k aana 35 1725 18 6231 4353 0 979417 54 05. 48 -077. 38 c 142b aar va 1 •V kaana 35 1457 13 6224 4159 3 979430 89 03 89 -076 62 c 143baar va 1 •Y baar atountai n 35 1486 18 6387 4104 0 979434 58 03 93 -076 44 c 144baar val • V baar aounta i n 35 1691 18. 6591 4077. 0 979436 91 04 63 -075 07 c I43baar va 1 •Y baar atountai n 35 1727 18 6422 4155 3 979430. 79 05. 44 -076 00 c 144b aar va 1 • Y baar aounta i n 35 1698 18 6469 4121 3 979432. 95 04 89 -076 18 c 147baar va I •V baar aounta i n 35 1740 18 6688 4297 3 979420. 89 06 38 -076 59 c 148baar va 1 •Y baar atountai n 35 1780 18 6714 4431 4 979408. 66 09 74 -077. 78 c 169baar va 1 •Y baar aounta i n 35 1764 18 6656 4516 1 979405. 99 08 12 -076 87 c 170baar va 1 •Y baar aounta i n 35 1635 18 6643 4062. 9 979437 60 04 05 -075 33 c 171b aar val •V baar atountai n 35 1667 18 6730 4313. 0 979420. 24 05. 60 -076. 46 c 173baar val •Y baar atountai n 35 1708 18 6764 4248 5 979422. 01 07. 13 -077. 36 c 174b aar va 1 * Y baar atountai n 35 1622 18 6739 4293. 3 979422. 45 05. 53 -075. 11 c 173b aar val •Y baar aounta i n 35 1579 18. 6702 4136. 3 979431. 91 04. 92 -075. 28 c 174b aar val •V baar aounta i n 35 1581 18 6741 4373 5 979416. 51 05. 63 -075. 80 c 177baar val •Y baar aounta in 35 1561 18 6667 4101 0 979434. 95 04 36 -074. 76 c 178baar val •Y baar aounta i n 35. 1457 18 6690 4747 5 979392 74 07 51 -074 29 c 179baar val •V baar atountain 35 1573 18 6655 4089. 2 979435. 84 04. 20 -074. 84 c 180b aar val •Y baar aounta in 35 1591 18 6616 4066. 9 979437. 63 03 72 -075. 02 c 181b aar va 1 •Y baar aounta in 35 1606 18. 6546 4049. 5 979439. 01 03 73 -074. 79 c 182baar val •Y baar aounta in 35 1640 18 6598 4047. 4 979438. 91 03. 82 -075 23 c 183baar va 1 • Y baar atountai n 35 1639 18 6510 4051. 2 979438. 74 03. 81 -075 16 c 184b aar va 1 •Y baar atountain 35 1656 18 6561 4045. 6 979438. 88 03. 77 -075. 54 c 183baar val •Y baar aounta in 35. 1640 18. 6537 4054. 2 979438. 57 03. 90 -075 23 c wall 8 b v baar Mountain 35 1644 18 6413 4072. 2 979437. 23 03. 37 -075. 90 c Mall 4 b v baar Mountain 35 1562 18 6370 4092. I 979436 12 03 14 -075 36 c Mall 4 b v k t ana 35 1514 18 6181 4120. 8 979434. 22 03. 04 -075. 23 c Mall 3 b v k * ana 35. 1539 18 6186 4111 9 979434. 53 03. 15 -075. 55 c Mall 2 b v k aana 35. 1560 18. 6229 4105. 9 979434. 71 03. 93 -075. 13 c Mall 1 b V baar Mountain 35 1590 18 6256 4115 4 979434. 04 03. 56 -075. 86 c Mall 24 b v kaana 35. 1573 18. 5935 4583. 5 979404. 16 03. 94 -077. 23 c Mall pvc b V k aana 35 1527 18. 6180 4112 1 979434. 60 03 08 -075. 43 c daartrai1 #23 baar Mountain 35 2114 18 7377 813. 0 979634 19 07. 39 -073. 45 c daartrai1 #24 baar Mountain 35 2105 18 7340 895. 0 979625. 96 08 01 -076. 10 c daartrai1 #23 baar Mountain 35 2097 18 7292 1012 0 979618 96 08. 41 -075. 65 c daartrai1 #22 baar Mountain 35 2064 18 7303 1192 0 979609. 38 08 56 -074. 07 c daartrai1 #21 baar Mountain 35. 2045 18 7297 1318. 0 979600. 52 08. 64 -075 17 c daartrail #20 baar Mountain 35. 2022 18. 7264 1492. 0 979590. 63 08. 95 -074. 19 c daartrail #19 baar Mountain 35 2016 18. 7242 1610. 0 979583. 73 09. 94 -073. 01 c daartrail #18 baar Mountain 35 2000 18. 7218 1766. 0 979573 18 10 30 -073 76 c daartrail #17 baar mountain 35. 1985 18 7220 1924. 0 979563 53 10. 42 -073. 73 c daartrail #16 baar mountain 35. 1957 18 7224 2054 0 979554. 00 10 59 -075. 09 c daartrail #13 baar mountain 35 1949 18. 7269 2259 0 979542 53 11. 45 -073. 40 c daartrail #14 baar mountain 35. 1939 18. 7267 2320. 0 979537. 94 10. 91 -074. 81 c 248 d aar ra 1 *13 baar aountain 35 1924 18 7234 2500 0 979524 54 12 23 -076 02 C d aar ra 1 *12 baar aountain 33 1931 18 7196 2680 0 979312 71 13 82 -075. 37 C d aar ra 1 «11 baar aountain 33 1945 18 7132 2871 0 979302 02 12 61 -076 19 C d aar ra 1 410 baar Mountain 33 1944 18 7121 3061 0 979489 83 13. 84 -075. 80 C daar ra 1 *09 baar Mountain 33 1938 18 7086 3197 0 979482. 47 12 44 -076 38 C daar ra 1 #08 baar aountain 33 1946 18 7039 3374 0 979471 21 12 80 -076. 78 C daar ra 1 #07 baar aountain 33 1963 18 7007 3316 0 979462 33 12. 01 -078 11 C daar ra 1 #06 baar aountain 35 1967 18 6988 3653 0 979433 86 12. 70 -077 62 C daar ra 1 90S baar aountain 33 1942 18 6965 3727 0 979430 46 12 35 -076 83 c d aar r a 1 904 baar aountain 33 1973 18 6939 3809 0 979444 31 13 48 -077 23 c daar ra 1 903 baar aountain 33 1987 18 6946 3935 0 979433 25 16 25 -076. 91 c daar ra 1 #02 baar aountain 33 1960 13 6907 4134 0 979424. 13 14. 04 -077 30 c daar ra 1 »01 baar aountain 33 1930 18 6876 4225 2 979419. 67 13. 32 -076 76 c •39 al 38 b ana 33 2638 18 6345 1797 6 979378 04 06. 06 -076. 67 B •40 al 38 b ana 33 2633 18 6300 1826 3 979574. 77 05. 77 -078. 30 B •41 al 38 bana 35 2633 18 6434 1884 7 979570 46 05 83 -079. 25 B •42 al 38 b ana 33 2623 18 6411 1905 2 979568 28 06 35 -079. 61 B •43 al 38 b ana 33 2619 18 6368 1974. 1 979362. 89 06. 44 -080. 74 B •44 al 38 bana 33 2629 18 6329 2064 9 979556. 06 06. 10 -082. 39 B •43 al 38 b ana 35 2638 18 6282 2122 3 979330. 73 06. 43 -084 22 B •46 al 38 oilar paak 33 2630 18 6239 2192 9 979543. 18 06. 87 -083. 07 B •47 al 38 oi lar paak 35 2619 18 6195 2244 5 979540. 83 07. 00 -086 11 B •48 al 38 oilar p aa k 35 2396 18 6137 2335 9 979336 33 07. 01 -084 75 B •49 al 38 oilar paak 33 2569 18. 6120 2426 1 979532 27 06. 07 -084 34 B • 30 al 38 oilar paak 35 2555 18 6078 2481. 8 979529 46 05. 28 -084. 49 B • 38 al 38 k aana 33 2397 18 3802 2524 7 979331. 36 04. 83 -078. 95 B #39 al 38 k a ana 35 2379 18. 3764 2305. 7 979531. 96 04. 61 -079. 75 B #60 al 38 k aana 35 2346 18 5745 2483. 5 979531. 33 04. 96 -081. 07 B •61 al 38 kaana 35 2323 18 5712 2514 1 979528. 95 05 12 -081. 26 B •62 al 38 kaana 35 2295 18 5678 2525 3 979529 30 04. 81 -080 31 B #63 al 38 kaana 33 2258 18 5675 2363. 6 979525. 44 04. 80 -081. 59 B •64 al 38 kaana 35 2228 18. 3639 2617 0 979320. 93 04. 93 -082. 33 B •63 al 38 kaana 33 2224 18 3393 2650. 4 979517. 32 04. 71 -084. 33 B #66 al 38 kaana 35 2202 18 5557 2697 5 979513. 26 04 85 -085. 23 B •67 al 38 kaana 33 2176 18. 5325 2733. 0 979510. 77 04. 73 -085. 32 B •68 al 38 k a ana 35 2148 18. 5497 2798. 0 979307. 16 04. 48 -085. 26 B •69 al 38 k aana 35 2127 18 3438 2828. 0 979505 10 03. 97 -083. 86 B •70 al 38 kaana 33 2108 18 3420 2862 3 979303. 46 04. 00 -083. 24 B •71 al 38 kaana 33 2090 18 3383 2890. 8 979302. 13 04. 04 -084. 70 B •72 al 38 k aana 35 2073 18. 3342 2907. 2 979501. 85 04 43 -083. 48 B •73 al 38 k aana 35 2049 18 3310 2961. 6 979498. 43 04. 37 -083. 28 B •74 al 38 kaana 35 2027 18 3273 3009. 1 979495. 49 04. 06 -083. 71 B •73 al 38 k aana 35. 2010 18. 3233 3063. 9 979493. 01 04. 27 -082. 37 B •76 al 38 k aana 33. 1993 18 3192 3114. 3 979490. 66 03 90 -082 12 B •77 al 38 k aana 33. 1971 18 3136 3162. 9 979487. 03 04. 21 -082. 34 B •79 al 38 kaana 35. 1925 18. 3089 3306. 0 979478. 63 04. 38 -081. 66 B •80 al 38 kaana 33. 1902 18. 3033 3349. 1 979473. 36 04. 03 -082. 31 B •81 al 38 kaana 35. 1872 18. 3031 3369. 0 979472. 77 04 39 -083 29 B •82 al 38 tahacha i n 33. 1842 18. 4993 3349. 2 979472. 49 03. 14 -083 75 B •83 al 38 tahac ha > 1 n 33. 1824 18. 4954 3331. 9 979472. 06 06. 00 -084. 21 B •84 al 38 tahacha i i n 33. 1816 18 4913 3328. 3 979470. 68 07 97 -083. 73 B •83 al 38 tahac hai i n 35 1805 18 4871 3360. 6 979467. 44 10. 04 -082. 90 B •86 al 38 tahac hai i n 35 1787 18 4834 3424. 6 979463 30 09. 09 -084. 02 B •87 al 38 tahac ha > i n 35 1765 18. 4802 3482. 7 979460 42 08. 17 -084 17 B •88 al 38 tahac ha ) i n 33 1738 18 4783 3341. 0 979459. 20 05. 73 -084. 11 B •89 al 58 tahacha ) i n 33. 1709 18 4754 3600. 8 979455 89 03. 73 -085. 60 B •91 al 38 tahacha i i n 33 1641 18. 4723 3682. 8 979448. 54 03. 78 -087. 43 B •92 al 58 tahacha ) i n 35. 1605 18. 4728 3723. 2 979443. 11 03. 35 -088. 57 B •93 al 38 tahacha i i n 33. 1368 18. 4728 3770. 2 979442. 61 02. 68 -088. 61 B •94 al 38 tahacha > i n 33. 1334 18 4709 3813. 1 979439. 75 02. 36 -088. 94 B 82/2 aa un ant arvin 33. 2065 18. 7906 464. 3 979635. 35 04. 11 -073. 74 D 249 250 ©©©©NiSNi£&&£££££££ppo~^~2~ijiu»uj^uojufrfrfrfr©©u©frfrfrfr^^^alaJal4l4l88i882£22 ( M M M 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C m C m C m C m • III rt #t rt rt * * * 3 3 3 1 1 1 t 1 * * * * » 3 3 3 3 3 33333333333333 »»»»»»*»»»*»»» 3 3 3 3 3 3 3 3 3 3 3 3 3 3 n n r> n r» r» nrtrtnrtnrtrtrtn 3 3 * » 3 3 n n r» n n n n n • •••33333333333 ****<<<<<<<<<<< 3 3 3 3 * * ■ M- M- * * • * » • M- M » * • M- t » - M- 3 3 3 3 3 3 3 3 3 3 3 » • i » o o o o CCCC 3 3 3 3 «r <t it »t * * * * 3 3 < < opoooooooooooooooooooooooooo W(OW»OUUU>***>f*>*UUi<JH«(JiO'9'9'Nj'J'jNjlO(D pt*©.ikfr©®P*-©N4frNi©pt*CJfr©'-©S©frfr4>©© O W ( M 0 *UlU( 0 CD'0 'JO'*(5 O-0 0> W 0'O'0 - 0 U*'JsjaiOl "4 (J (J S CJ © 18. 18. © © © CD © © © © © © CD © CD C D© © © © © © © C D© C D© © © m © f r fr fr fr f r f r fr fr f r fr fr fr £ fr f r fr fr fr £ £ £ £ fr fr fr fr S Ni s S s S p P f ►» © © Jk 4k Jk © © © O ' fr fr S S S © © mm 4444 O P p M fr* frfr © fr P © © s © fr 4 ►» © © p 4k fr P © © o w fr © © fr fr © f r f r © © ►» fr Ni © © © © © © © *> fr ►» p fr 4t s © © ►» ■* ■* © U U f r f r P f r © v| Ni © fr s © C J C J© © © © © © © © © © © © © © © © © 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CJ 4 © fr N i fr 44 4 14) 4 1 N| N i N | ■ "i S 4 14 14 144 © © © © fr fr fr fr S 8 S p © fr o S S n| n| n| >J n| n| Ni n| CD © OD 00 woua-oowu'j 'J W 4 «(* v| O t* I* U *> » » p . *> + . g n| s © © S f r B ' 0 " J W W s l f 4 4 4 4 4 4 4 S S S N| Ni N| Ni 4 4 4 4 4 4 4 0> > 0k0,(h0'(h0'0> ' CD f ^UIOI fflOU* — — OOt-U> ■ 0 1 0 © O' f* w K (J H S CJ *■* *■* fr S I I i O O O fr fr fr O' © O' O' O' t- fr O S fr S 4> CJ M t* O 0 0 4 U O Q I U U 4 4 ( 1^0*0 f» CJ >1 fr fr Oi O- U 4 O' * 0 S © M 4 I I o o O' O' O' n | 00 S © © ►* CJ CJ O' OOO © NI N< 0 0 4 fr CD O' n | 1 I I OOO O' O' O' tn - N i Nj fr O' "4 fr fr nJ Ni O S fr WO'O'SO'W'O'Osps'Oigt- frt-frWmpfrWfriFcj-Ofr© 0000000000000*3 oi ►* o a* ►» 4 1 t» u O O O Q O O Ni N| OD 5 4 © *-*©*■*©© 4) vlUOIi'Ht* I 1 I I I I O O O ‘ 'O (J 0> 1 0 POO O' O' O' O' m O' 8 § 8 ; 3 i o o o o o o n OI * 0 fr © fr © fr t-© CJ P P P P © frO' © © s frfr © •-*© 4> 1 1 1 p fr£ © fr (J* © ©* fr fr frt*© D 0 D o 400*4 0 4 CJ O O' Q Q O t - * f* •*©•000 (P ( J ) M M *« © © fr OD fr 1 1 I I I g | m fr O' Ni Ni 4 4W**4W © O CJ © © £ £ u sss S © © 4 4 0D I I I OOP Ni Nl fr 0 0-0 2 S 3 f U O M 4 4 U O UUOUU43>* OQO Nl O' © O O' « 0 1 I I I OOO S Ni Ni *>mo * - * © fr © CJ CJ 0 O O O o © fr fr fr f r O' -0 O' 01 * © W Nl «-* ►* 1 I I I I o o o o o N| N| N| >| Ni O' S Nl Nj O' O' © CJ O CJ • 0 fr t- © - 0 oaaaoooooooooooo 82/1 U | u n *nt «rvin 3S 2041 118 7889 462 3 979, 45/1 »« un ant c umeti ng * at 35 0189 18 5992 3551 4 979458 10 08 61 -068 57 D 44/5 ms un s n t cuaaainga at 33 0180 18 5956 3338 3 979457 35 08 66 -068 78 D 44/4 ms un ant C U M inga at 33 0172 19 3934 3344 4 979457. 67 08 88 -069. 01 D 44/3 ms un ant c uauainga at 33 0164 IB 5904 3513 4 979458. 57 09 20 -069 46 D 44/2 ms un ant c uaa1 n g a a t 35 0134 18 5867 3553 9 9794 56 OO 09 09 -069 75 D 44/1 ms un an t C UtiMKinga at 33 0146 18 5839 3602. 6 979452 80 09 36 -069 70 D 43/3 ms un ant cuaaing* at 33 0127 18 5811 3592 7 979453. 54 08 75 -070 00 D 43/2 e# un ant c uawainga at 33 0093 18. 5764 3801 8 979442. 04 08 56 -068 91 D 43/1 ms un ant c uaainga at 35 0062 19 5719 3891. 6 979436. 75 07 99 -069 14 D 42/4 ms un ant c uaainga at 33 0031 13 5676 4472 1 979400. 98 07. 95 -069 99 D 42/5 ms un ant c uaainga at 33. 0026 18 5666 4428 1 979404 91 06 54 -070 05 D 42/4 ms un ant c uaainga at 35 0015 18. 5644 4466 9 979402 41 04 89 -071. 80 D 42/3 ms un ant 1 lab a twin 34 9992 18 5600 4666 6 979390 23 05. 21 -071. 51 D 42/2 ms un ant 1 iab a tain 34 9984 18 5585 4786 4 979382 79 05 07 -071. 86 D 42/1 ms un ant 1 iak a tain 34 9970 18 5557 4906. 9 979374. 90 04. 80 -072. 70 D 61/7 aa un ant 1 lab a twin 34 9954 18 5525 4990. 9 979368 57 06. 46 -072 21 0 61/6 ms un ant 1 lab a twin 34 9936 18 3488 4954. 1 979370. 24 06 41 -072. 63 0 61/5 ms un ant 1 i ab a twin 34 9930 18 5475 4833. 3 979376 49 06 41 -073. 55 0 61/3 ms un ant 1 lab a twin 34 9914 18. 5444 5134 3 979357 22 06 46 -074. 63 D 61/1 ms un ant 1 lab a twin 34 9905 18 5426 5424. 9 979338 20 06. 80 -075 84 D 40/3 ms un ant 1 iab a twin 34 9863 18 5393 5237 3 979350 33 04. 58 -076. 80 D 40/2 ms un ant 1 i ab a twin 34 9828 18 5364 5066 4 979358. 83 05 23 -077. 59 D 40/1 a s - a un ant 1 lab a twin 34 9763 18 5313 4938 1 979360. 03 05 51 -083 25 D 59/4 ms un ant I iab a twin 34 9736 18. 3290 5094 0 979349. 80 04. 57 -084 84 D 59/3 ms un ant 1 i ab a twin 34. 9710 IS 5273 5125 1 979345 43 04 75 -086 96 D 59/2 ms un ant 1 iab a twin 34 9690 18. 5259 4913. 7 979356 24 05 09 -088. 29 0 59/1 ms un ant 1 lab a twin 34 9631 18 5218 4734 9 979365. 78 04 31 -089. 72 D 56/5 ms un ant 1 i ab a twin 34. 9610 18 5203 4562. 2 979375. 64 04. 46 -089 87 D 58/4 ms un ant 1 iab a twi n 34. 9595 18 3193 4448 0 979382. 53 03 89 -090 24 0 38/3 ms un ant 1 iab a twi n 34 9571 18 5175 4277. 2 979392 42 03. 27 -090. 98 D 58/2 ms un ant 1 i ab a twin 34. 9551 18. 5162 4197. 9 979397. 46 02. 90 -090 88 D 38/1 ms un an t 1 i ab a twin 34 9515 18. 5136 4130. 2 979398. 42 02. 70 -093. 87 D 37/4 ms un ant 1 iab a twin 34. 9471 18 5105 4021. 1 979404. 45 02 56 -094. 12 D 37/3 ms un ant 1 iab a twi n 34 9452 18 5091 3958 3 979408. 03 02. 32 -094 37 D 57/1 ms un ant 1 iab a twin 34 9390 18 5047 3937. 8 979404 67 02 71 -098 05 D 56/4 ms un ant 1 i ab a twin 34. 9348 18. 5018 3875. 6 979406. 16 02. 44 -100. 19 0 56/3 ms un ant 1 iab a twin 34. 9335 18. 5008 3839. 4 979407. 92 02 44 -100 48 D 56/2 ms un ant ty 1 a horaa yn 34 9289 18 4977 3788 2 979408. 91 02. 95 -101. 66 D 56/1 ms un ant tyla horta yn 34 9260 18 4955 3796. 5 979406. 70 02. 60 -103. 47 0 55/4 ms un ant tyla horaa yn 34. 9240 18 4942 3759. 1 979407. 99 02. 69 -104. 16 D 33/3 ms un ant tyla horaa yn 34.9195 18. 4910 3611. 2 979415. 94 02 65 -104. 71 D 53/2 ms un ant ty 1 a horaa yn 34 9180 18 4898 3£75. 9 979410. 94 02 76 -105 60 0 53/i ms un ant ty la horaa yn 34. 9137 18 4880 3599. 1 979415. 25 02. 53 -105. 92 0 54/4 ms un ant ty la hona yn 34 9114 18 4845 3562 0 979416. 07 02 00 -107. 48 0 54/3 ms un ant ty 1# horaa yn 34. 9080 18. 4817 3480 7 979429. 55 02 19 -107. 38 D 34/2 ms un ant ty la horaa yn 34. 9037 18. 4782 3416. 4 979423. 30 01. 49 -108. 81 D 54/1 ms un ant ty 1 a horaa yn 34. 9013 18 4762 3382. 9 979424. 94 01. 40 -109. 07 D 53/4 ms un ant ty 1 a horaa yn 34. 8986 18. 4740 3391. 8 979423 40 01. 40 - r l 09. 83 D 33/3 ms un ant tyla horaa yn 34 8951 18.4711 3316 1 979424. 43 01. 36 -113. 08 D 53/2 ms un ant ty la hona yn 34. 8922 IS 4688 3319 7 979426. 78 01 21 -110. 41 D 33/1 ms un ant tyla horaa yn 34 8895 18. 4665 3295. 5 979427. 80 01. 23 -110. 58 D 32/3 ms un ant tyla horaa yn 34 8869 18 4645 3279. 7 979428 32 01 20 -110. 82 0 32/4 ms un ant tyla horaa yn 34. 8846 18. 4626 3318. 6 979425 13 01. 33 -111. 37 D 32/3 ms un ant tyla horaa yn 34 8825 18. 4608 3352. 8 979422. 00 01. 57 -112 03 0 32/2 * s un ant tyla horaa yn 34 8794 18. 4 582 3269 0 979426. 33 01. 73 -112. 28 D 32/1 ms un ant tyla horaa yn 34 8777 18. 4568 3189. 7 979431. 64 01. 99 -111. 31 D 51/3 ms un ant tyla horaa yn 34. 8757 18. 4553 3092 5 979436. 70 01 88 -112. 00 D 31/4 ats un ant fair ont butta 34 8726 18. 4530 2979. 0 979442 56 01. 75 -112. 79 D 31/3 ms un ant fairnont butta 34. 8703 18.4512 2925. 4 979440 62 01. 60 -117. 88 D 31/2 ms un ant fairaont butta 34. 8685 18. 4497 2881. 7 979446. 10 01. 49 -114. 97 D 31/1 ms un ant fairaont butta 34 8663 18. 4479 2842. 2 979447. 70 01. 52 -115. 51 D 251 50/6 U(un «nt dairvont bu 50/9 Mfun «nt fairvont bu 14/3 pa d-pa waad patch 14/4 pa d-p a vaad patch 15/1 pa d-pa vaad patch 15/2 pa d-pa vaad patch 15/3 pa d-pa vaad patch 16/1 pa d-pa vaad patch 16/2 pa d-pa va a d patch 16/3 pa d-pa «a 111 a r 16/4 pa d-pa •attlar 17/t pa d-pa a«111 a r 17/2 pa d-pa •attlar 17/4 pa a#111ar 18/1 pa d-pa •attlar 18/2 pa d-pa •attlar 18/3 pa d-pa •attlar 18/5 pa d — p a aattlar 19/1 pa d—pa aattlar 19/2 pa d-pa aattlar 19/3 pa d—pa aa 111ar 19/4 pa d-pa aattlar 20/1 p* d-pa aattlar 20/2 pa d—p a aattlar 20/3 pa d-pa aattlar 20/4 pa d—p a aattlar 21/1 pa d-pa aattlar 21/2 p* d-pa aattlar 21/3 pa d—p a aattlar 21/4 pa d-pa tajon hill 22/1 pa d—p a ta jon hill 22/2 pa d—p a tajon hill 22/3 pa d—p a tajon hill 22/4 pa d —p a tajon hill 23/1 pa d —pa tajon hill 23/3 pa d —p a tajon hill 23/4 pa d —p a tajon hill 24/1 pa d—p a tajon hill 24/2 pa d-pa ta jon hill 24/3 pa d —p a ta jon hill 24/4 pa d —pa tajon hill 25/1 pa d —pa tajon hill 25/2 pa d—pa paatoria c 25/3 pa d-pa paatoria c 25/4 pa d-pa paatoria c 26/1 pa d-pa paatoria c 26/2 pa d-pa paatoria c 26/3 pa d-pa paatoria c 26/4 pa d-pa paatoria c 27/1 pa d—pa paatoria c 27/2 pa d—pa paatoria c 27/3 pa d-pa paatoria c 27/4 pa d — p a paatoria c 28/1 pa d-pa paatoria c 28/2 pa d-pa paatoria c 28/3 pa d-pa paatoria c 28/4 pa d—pa paatoria c 29/1 pa d—p a paatoria c 29/2 pa d-pa paatoria c 29/2a p rd-p a paatoria c a 34 8643 18 4463 2815 a 34 8624 IS 4447 2785 35 1511 18 9030 377 35 1475 18 9038 382 35 1440 18 9028 388 33 1406 18 9019 394. 33 1368 18 9007 399 35 1294 18 8985 412 33 1256 18. 8974 420 35 1223 18 8963 427 35 1198 18 8953 437 35 1132 18 8942 442 35 1115 18. 8931 451 35 1079 18 8920 461 33 1043 18 8909 469 35 1008 18 8898 480. 35 0972 18. 8387 492 35 0936 18. 8877 501. 35 0898 18 8865 511 35. 0S64 18 8855 518 35 0826 18 8844 528 35 0790 18. 8833 540 35 0735 18 8822 552. 35 0737 18 8817 562. 35 0702 18 8807 575 33. 0666 18. 8796 587. 35 0630 IS 8785 602. 35. 0594 18. 8775 617 35 0537 18 8762 633 35 0521 18. 8732 648. 35 0482 18. 8742 663. 33 0463 18 8737 672. 33 0443 18. 8739 680. 35. 0409 18. 8729 694. 33. 0374 18. 8718 706. 33 0301 18. 8696 737. 35. 0230 18. 8675 763. 35 0193 18. 8665 772. 33 0158 18 8654 785 33. 0122 18. 8644 795. 35 0086 18. 8634 805. 33 0050 18. 8623 820. 35. 0014 18 8613 837. k 34. 9980 18. 8604 849. k 34. 9943 18. 8393 860. k 34 9918 18. 8584 879. k 34. 9883 18 8575 895. k 34. 9837 18. 8561 912. k 34. 9801 18. 8550 929. k 34. 9763 18. 8539 941. k 34. 9733 18. 8530 960. k 34 9693 18. 8518 982. f c 34. 9664 18 8509 991. k 34. 9643 18. 8502 1005. k 34. 9603 18. 8491 1013. k 34. 9568 18 8481 1044. f c 34. 9528 18 3468 1078. k 34. 9509 18. 8463 1097. k 34. 9479 18. 8434 1140. k 34. 9434 18 8443 1183. k 34. 9418 18. 8438 1221. 1 97944-8 66 01 48 -116 02 D 8 979449 77 01 47 -116 53 D 8 979647. 46 02 48 -085 90 D 3 979646 61 02 49 -086 18 D 9 979645 66 02 61 -086 31 D 4 979644. 77 02 61 -086 59 D 2 979643 96 02 73 -086 67 D 5 979642 11 02 73 -087 10 D 0 979641.21 02 85 -087 11 D 0 979640.36 02 86 -087 25 D 6 979639 50 02 86 -087 18 D 8 979638 73 02. 86 -087 33 D 5 979637. 87 02 83 -087 40 D 7 979637 07 02. 83 -087. 29 D 5 979636 42 02. 83 -087 16 D 7 979635. 50 02, 95 -087. 00 D 5 979634.64 02 95 -086 85 D 9 979634 03 02. 95 -086. 59 D 4 979633 37 03. 06 -086 25 D 8 979633. 04 03. 06 -085 85 D 5 979632. 39 03 07 -085 60 D 9 979631. 36 03 04 -085. 62 D 9 979630. 39 03 02 -085. 59 D 2 979629. 73 03 02 -085. 55 D 8 979628. 77 03 13 -085. 29 D 3 979627. 98 03 13 -085. 09 D 5 979626. 95 03 13 -084. 91 D 0 979625. 92 03. 13 -084. 76 D 6 979624. 71 03. 14 -084.67 D 5 979623 62 03. 16 -084. 54 D 7 979622.49 03 16 -084. 43 D 0 979621. 99 03. 19 -084. 25 D 1 979621.37 03. 19 -084.23 D 4 979620 39 03 19 -084 06 D 8 979619 56 03 30 -083. 74 D 7 979617.63 03 31 -083 20 D 5 979616. 06 03. 28 -082. 66 D 5 979615. 61 03. 24 -082. 30 D 1 979615.01 03.25 -081.85 D 5 979614.61 03.29 -081.28 D 5 979614. 77 03. 32 -080. 19 D 1 979613. 47 03. 43 -080. 20 D 9 979612 50 03. 45 -079. 78 0 O 979612. 02 03. 49 -079. 28 D 7 979611 62 03. 55 -078 62 D 3 979610. 74 03. 39 -078. 33 D 9 979610. 30 03. 61 -077. 28 D 8 979610. 10 03. 71 -075. 96 D 7 979609. 93 03. 82 -074. 71 D O 979609. 81 04. 02 -073 66 D 7 979608. 31 04. 01 -073 71 D 0 979608. 21 04. 11 -072. 12 D 7 979607. 88 04. 32 -071. 41 D 5 979607. 42 04 32 -070. 86 D 9 979607. 29 04 76 -069. 59 D 9 979606.01 04 89 -068.72 D 4 979604. 59 04. 98 -067. 72 D 4 979603. 77 04. 02 -068. 20 D 1 979601. 66 05. 39 -066. 14 D 1 979599. 41 05 72 -065. 00 D 1 979598. 41 05. 98 -063. 46 D 252 29/3 par -pit pat tori c raa k 34 9398 18 2134 1237 6 979597 19 06 14 -063 36 D 29/4 par —p a t pat tor i c r aak 34 9380 18 8429 1274 1 979595 77 06 42 -062 17 D 29/3 par -pat pat tor 1 crtak 34 9362 18 8425 1302 9 979594 58 06 49 -061 43 D 29/6 par — pat pat tori cr aab 34 9344 18 8421 1325 9 979593 48 06 79 —060 70 D 30/1 par -pat pat tor 1 c r aa k 34 9323 IB 8417 1351 6 979591 58 07 62 -060 05 D 34/1 par -pat pat torl c r aa k 34 8845 18 8075 3430 3 979463. 50 06 73 -060 92 D 34/2 par -pat pat terl craak 34 8828 18 8075 3436 7 979462 86 04 86 -062 89 0 34/3 par -pat pat tor i craak 34 0816 18 8075 3405 9 979464 27 04 56 -063 53 D 34/4 par -pat patterl c r aa k 34 8765 18 8074 3356 4 979464 85 05. 14 -064 89 D 34/3 par — pat iebac 34 8744 18 8073 3551 4 979451. 87 03 84 -067 35 D 34/6 par -pat 1 ab ac 34 8732 18 8073 3552 4 979451 07 03 82 -068 00 D 33/1 par -pat labac 34 8716 18 8073 3456 5 979456 10 03 89 -068. 50 0 39/2 par -pat lebec 34 8688 18 8073 3425. 4 979455 63 04 73 -069. 75 D 33/4 par -pat labac 34 8647 18 8072 3599 2 979443 23 04. 45 -071 69 D 33/5 par -pat labac 34 8600 18 8071 3657 7 979438 53 04 10 -072. 86 D 36/1 par -pat 1 ab ac 34 8574 18 8071 3755. 6 979432 07 03. 04 -074 30 D 36/3 par -pat labac 34 8530 18 9070 3640. 1 979438 87 03 26 -073 81 D 36/4 par -pat labac 34 8506 18. 8070 3628. 0 979439 00 03 12 -074. 34 D 36/3 par -pat labac 34 8486 18 8069 3636 5 979437. 60 03 69 -074. 49 D 36/6 par -pat labac 34 8463 18 8070 3652 8 979435 39 04. 21 -075. 02 0 37/i par -pat labac 34. 8427 18 8069 3877 6 979420 44 03 95 -076. 50 D 37/3 par —pat labac 34. 8390 13 8070 4080. 9 979406. 70 04. 33 -077. 39 D 37/3 par -pat labac 34. 8338 18 8069 4259. 5 979393. 99 03 89 -079 43 0 37/6 par -pat 1 ab ac 34 8323 18 8069 4313. 6 979390. 56 03 25 -080 13 D 37/7 par —pat 1 ab ac 34 8297 18 8068 4363. 7 979386. 89 03. 03 -080. 80 D 38/1 par —pat 1 abac 34 8273 18 8067 4335 8 979388 16 03. 40 -080 63 D 38/2 par —p a t labac 34 8255 18 8066 4207 6 979395. 75 02. 71 -081. 24 D 38/3 par — pat 1 abac 34 8235 18. 8065 4120 8 979400. 78 02. 49 -081. 45 D 38/3 par —pat 1 ab ac 34. 8193 18 8063 4167. 3 979396 78 02. 39 -082. 42 D 38/6 par —p a t labac 34 8176 18. 8059 4141. 2 979397. 79 02. 26 -082. 95 D 38/7 par —pat lab ac 34 8153 18 8055 4143. 2 979397.14 02. 91 -082. 64 D 39/1 par —pat 1 abac 34.8143 18. 8052 4147. 1 979396 80 02. 52 -083. 06 D 39/2 par — pat 1 abac 34 8094 18 8041 4343. 1 979382. 55 03. 91 -083. 78 D 39/3 par — pat 1 ab ac 34 8074 18. 8037 4472. 7 979373. 99 04. 25 -084. 09 D 39/3 par — pat 1 ab ac 34 8051 18. 8033 4604. 3 979364 56 05. 15 -084. 55 D 39/6 par — pat 1 ab ac 34 8022 18 3014 4694. 9 979357. 62 05. 00 -085. 98 D 40/1 par — pat lab ac 34 7992 18. 7994 4626. 4 979360 87 05. 05 -086. 52 D 40/2 par — pat lab ac 34 7959 18 7970 4583. 7 979362. 06 04. 34 -088. 35 D 40/3 par —p a t labac 34 7934 18 7954 4495. 7 979366 93 04. 03 -088. 83 D 40/4 par — pat 1 ab ac 34 7902 18. 7933 4480. 8 979365. 88 05. 72 -088. 78 D 41/1 par —p a a 1 ab ac 34. 7877 18. 7916 4351. 6 979372 26 05. 89 -089. 75 D 41/2 par — pat labac 34. 7847 18 7894 4132. 2 979385. 24 05. 16 -090. 36 D 41/3 par —pat labac 34 7830 18. 7882 4001. 5 979393. 16 04. 42 -090. 85 D 41/4 par —p a t labac 34 7803 18. 7864 3835. 2 979402. 62 04. 07 -091. 46 D 41/3 par — pat 1 abac 34 7795 18 7859 3776. 1 979405. 98 03. 93 -091. 70 D 41/6 par — pat lab ac 34 7766 18. 7839 3535. 8 979419. 95 03. 19 -092. 58 D 42/1 par —pa t lab ac 34 7741 18. 7821 3367. 2 979429. 24 02. 42 -093. 92 D 42/2 par — pat 1 ab ac 34. 7716 18. 7803 3296. 4 979430. 05 02. 00 -097. 55 D H 2736 arvin 35. 1257 18. 7526 2756 0 979520. 73 07. 47 -063. 65 E I 2173 baar mountain 35 2393 18. 6767 2175 0 979556 22 08. 21 -071.74 F •ar t baar mountain 35. 1290 18. 7428 3367. 0 979478. 13 11. 77 -065. 74 Q H 3433 baar mountain 35 1343 18 7278 3433. 0 979475. 58 06 73 -069. 83 E H 4136 baar mountain 35. 1677 18. 6834 4516 0 979401. 34 10 85 -078. 06 E H 4741 b aar mo un ta i n 35 1661 18. 7125 4741. 0 979383. 33 17. 59 -075. 73 E black oak baar mountain 35 1618 18 6964 5129. 3 979360. 74 15. 02 -077 30 C H 4626 baar mountain 35. 1616 18 7152 4624. 0 979392. 08 15. 10 -076. 09 E H 3836 baar mountain 35 1377 18. 6974 3856. 0 979447. 39 05. 23 -074. 53 E H 4017 baar mountain 35 1381 18. 7042 4017. 0 979437. 17 07. 95 -072. 44 E H 3947 baar mountain 35 1480 18. 7262 3947. 0 979442. 97 09. 20 -070. 42 E H 3966 baar mountain 35 1432 18.7121 3966 0 979439. 79 07. 74 -073. 52 E BH 1732 bana 35 2748 18 6356 1729. 9 979576. 33 06. 76 -082. 65 0 253 Mi 1451 bana 33 2729 18 6439 1651 1 979383 24 03. 36 -081.69 G BH 1500 b «n« 33 2801 18 6473 1380 3 979386 97 OS 23 -082 91 G BH 1410 bana 35 2890 18 6416 1407 0 979593 46 OS 44 -087 31 0 H 2348 b ana 33 2363 18 6362 2346 0 979344 24 08 81 -074 23 E H 2235 b ana 33 2666 18 6769 2233 0 979333 09 06 27 -071 33 E H 2234 bana 33 2383 18 6798 2236 0 979557 33 05. 82 -069 82 E H 1937 b aan 33 2733 18 6342 1937 0 979566. 34 06 34 -080 36 E H 2177 bana 33 2678 18 6365 2177 0 979551 31 06. 32 -000 84 E H 2429 b ana 33 2332 18 6878 2629 0 979329 37 11 47 -069 42 E H 2040 bana 35 2620 18 6957 2060 0 979570 25 06 48 -068 24 E H 1317 bana 33 2733 18 6342 1317 0 979602 73 04 87 -070 98 E H 1203 b ana 33 2701 18.7217 1205 0 979621 04 04 54 -071. 06 E H 1148 b ana 33 2572 18 7332 1148 0 979622 13 07 76 -069 06 E H 1986 b ana 33 2338 18 6701 1986 0 979371 06 03 92 -071. 88 E I 3873 c uaainga at 33 0131 18 5617 3873 0 979434 64 10 65 -070. 34 F I 4027 c u m Inge at 33 0163 18 5329 4027 0 979424. 39 09 04 -073. 02 F H 4333 cuaainfc at 33 1044 IB 5236 4333 0 979400 16 04. 09 -078 28 E BH 3092 fine* cuaaing « at 33 0906 18 3418 3092 0 979366. 98 06 89 -073. 38 G H 3127 cuaaing* at 33 0840 18 3531 3127 0 979366 72 08 20 -071. 68 E H 4577 cuaaing* at 33 0902 18. 3621 4377. 0 979402 66 06 13 -071 21 E I 4266 c u.aaingi at 33 1169 18 5386 4266 0 979418 83 02 36 -079 67 F BH 7EAH cuaaingt at 33 1172 18 5474 4255. 0 979422 48 02 35 -076 74 G BH 4490 jail cuaaing* at 35 121 1 18 5339 4490 0 979406 30 06. 74 -074 60 G I 3833 cuaaing* at 33 1235 18 6008 3833. 0 979430. 37 02 41 -074. 33 F S 3898 cuMlngt at 33 1234 18 6133 3898. 0 979447. 96 02 78 -072. 69 E I 3791 c uaalngt at 33 1019 18 6193 3791 0 979451. 93 02 35 -073. 71 F I 3820 cuaaingt at 33 0946 18 6102 3820 0 979448. 52 02 81 -074. 32 F BH 6EAH c unaingf at 35 1237 18 5922 3844 2 979448 19 02 27 -076 21 0 I 3902 c jMlngt at 33 0946 18 3926 3902 0 979443. 29 03 43 -074. 03 F I 4037 c uaai ng* at 33 0938 18 3832 4037 0 979433. 94 03 39 -074. 09 F H 4728 c uaainga at 35 0766 18 6Q40 4728 0 979389 28 09 78 -070. 78 E H 3723 c uauai nga at 33 0689 18 5357 3725 0 979326 46 12. 33 -070. 74 E H 6013 cuaaing* at 33 0623 18 3432 6013 0 979309. 02 07. 92 -074.78 E H 6673 c urmbi ng a at 33 0455 18.5413 6675 0 979262. 60 15. 18 -072. 87 E H 6840 c uaainga at 33 0498 18 3208 6360 0 979249. 85 15. 33 -074. 75 E H 3277 c uaaings at 35 0737 18. 5546 3277. 0 979333. 36 07. 94 -073. 23 E H 3396 cuaainga at 33. 0744 18. 3236 3596 0 979333. 97 08 33 -075 42 E BH 5329 tfcar cuaualnga at 35. 0858 18 3072 5329 0 979335. 34 07 OO -080. 13 G H 4921 cuaainga at 33 0937 18 3066 4921. 0 979374. 71 06 10 -078. 94 E H 6383 cuaualnga at 33. 0465 18. 3034 6385 0 979270 91 14 28 -070 94 E H 6627 c uauai ng a at 33 0378 18. 3017 6627. 0 979262 60 16. 97 -073. 31 E H 6308 c uauai ng a at 35. 0635 18. 3080 6308. 0 979286 38 13. 11 -074. 67 E I 4161 c uauai ng a at 33 1161 18 3139 4161. 0 979423 19 02. 94 -078. 96 F BH 0/202 c uaai ng a at 33 1228 18 3740 3886. 7 979446. 92 02. 48 -074. 66 G BH 14/202 c uauai ng a at 33 1239 18 3378 4384 3 979411. 71 03 66 -079. 03 G BH 16/202 c uaai nga at 33 1212 18 5341 4360. 0 979413. 40 03. 45 -078. 78 G BH 21/202 cuaualnga at 33 1129 18 3216 4262 3 979418 99 02 68 -079. 08 0 w 11 4 (• 1 ) cuaualnga at 33 1170 18 3030 4162 2 979423. 33 02 14 -081. 62 H m 11 3(r1) cuaualnga at 33 1097 18 3073 4209 7 979419. 80 02. 40 -081. 44 H 9 0 11 6(h1) cuaualnga at 33 1046 18 3068 4302. 0 979413. 81 02 69 -081. 19 H 9 0 11 7 C c1> c uauai ng a at 33. 1091 18 5123 4192. 2 979421 60 02 31 -080. 52 H m 11 8 (4 1) c uauai nga at 33. 1097 18 3293 4343 2 979413 03 02 17 -080 46 H m 11 13(11) cuaualnga at 33. 1137 18 6203 3793. 8 979452. 41 02. 36 -074.06 H m 11 14(11) c uauai nga at 33 1164 18 6011 3813. 2 979449. 82 02. 25 -073. 72 H 9 0 11 15(p2 > c uaa inga at 33 1099 18. 6020 3831 3 979448. 06 02. 17 -076. 03 H 9 0 11 16(a 1 ) cuaainga at 33 1077 18 3927 3836. 1 979446. 41 02. 53 -075. 67 H 9 0 11 17(j1) cuaualnga at 33 1011 18 6104 3810. 9 979449. 03 02. 49 -073. 21 H 9 0 11 18(al) cuauai nga at 33 1206 18 3926 3828. 9 979449. 04 02. 20 -076. 08 H 8 4311 grapavina 34 8931 18 8874 4311 0 979404. 77 08 08 -054. 43 E 8 4603 grapavina 34 8946 18 8836 4605. 0 979397. 66 09 43 -054 69 E FAA grspavina 34 9032 18. 9033 4811 7 979373. 74 17. 80 -038. 60 G 254 OOOX(»iiJOOOUJUJlJJlkU.U.U.IkUJUiUiU.U.UJUJUiUi n -4 © n © p ♦ p n fr ra 4 4 M )N O # - ♦ n n n -4 r 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X X XX xxxxxx c iMflMtitiMAttgttiaaMa 255 H 3336 la li* r t r n 34 8468 18 6841 3336 0 979424 21 01. 97 -106 21 E H 3362 la 11* r t r n 34 7870 18 7460 3361. 3 979423 84 01. 48 -099. 69 E DM 3367 It 11* r t r n 34 8393 18 7206 3367. 1 979434 26 02 28 -094 37 0 DM 3382 fluth la lit rt r n 34 8284 18 7289 3382 0 979428 91 02 00 -098 38 0 H 3384 It lit r t r n 34 8423 18 6914 3384 0 979423 99 01 82 -104 33 E DM 3408 la lit r # r n 34 7649 18 7272 3410 0 979421. 39 01 88 -098 78 0 I 3436 it lit r t rn 34 8619 18 6429 3436 0 979416 22 01 68 -110. 99 F I 3432 It lit rt r n 34 7713 18 7234 3432 0 979418 98 01 98 -099 34 F H 3477 It lit rt r n 34 8231 18 7376 3477 0 979423 38 02 27 -097 01 E H 3684 It lit rt rn 34 8379 18 6883 3684 0 979412 22 03 10 -098. 42 E H 3728 It lit r t rn 34 8663 18 6791 3728 0 979411 30 03 61 -096. 71 E H 3744 It 1i tbr t rn 34 8708 18. 6471 3749 0 979403 03 03 13 -104 79 E H 4104 It 1i tbrt r n 34 8714 18 6938 4189 0 979387. 12 04 10 -093 46 E DM 3323 1 tb tc 34 7730 18 7723 3323 3 979431 99 02 04 -094. 26 0 DM 3330 1 tb tc 34 7730 18 7663 3348 3 979430 11 01 86 -094 81 0 DM 3383ir**tt > 1 tb tc 34 7735 18 7782 3382 0 979428 93 02 45 -093. 44 0 DM 3430 1 tb tc 34 7822 18 7337 3449.9 979422 13 01 44 -097 75 0 DM 3463 1 tb tc 34 8434 18 3689 3462. 6 979436 13 03. 94 -063 83 C DM 3313 1 tb tc 34 7843 18 8147 3513. 0 979426 34 02 72 -088 69 C H 3688 1 tb tc 34 8270 18 8490 3688 0 979433. 23 03 03 -072. 60 E H 3802 1 tb tc 34 8083 18 7638 3802 0 979405. 47 03. 42 -093 62 E H 4120 I tb tc 34 8334 18 8232 4120. 0 979412 17 02. 70 -072 39 E H 3363 1 tb t c 34 7788 18 7397 3362 0 979416 30 01. 80 -096 24 E BM 3380 1 tb tc 34 8002 18 7520 3579 5 979412 21 02 01 -100 88 G DM 3386 1 tb tc 34 7781 18 7897 3586. 0 979418 33 02 49 -092. 02 0 BM 4240 1 tb tc 34. 7878 18 7818 4240. 0 979377. 39 04 37 -092 82 G H 4374 1 tb tc 34 8703 18 8243 4374. 0 979401. 00 03 23 -067. 31 E H 4383 1 tb tc 34 8333 18 8181 4383. 0 979387 73 04 27 -077. 78 E H 4340 1 tb tc 34 8603 18 8627 4390. 0 979399. 43 08. 83 -063 47 E H 4628 1 tb tc 34 8533 18 8373 4628 0 979380 32 09. 93 -066 63 E H 4814 1 tb tc 34 8030 18 8433 4812. 7 979353 81 07 65 -080.16 E H 4871 tijon 1 tb tc 34 8036 18 9146 4870. 0 979347. 09 06. 84 -084. 31 E H 4416 2 tb tc 34 8323 18 7946 4916. 0 979343. 33 11. 99 -080. 60 E H 4782 1 tb tc 34 8074 18 8665 4782 0 979363 40 06. 64 -073 78 E H 4404 11 b tc 34 8048 18. 8618 4906 3 979351. 77 07 74 -076 66 E BM 4700 (*976 > 1 tb tc 34 8324 18 7742 4692 6 979362 30 08 85 -081 83 G H 3086 1i tbrt twin* 34 9804 18 3504 3086. 0 979357 72 04. 35 -078 21 E H 3213 11tbr t twin* 34 9431 18 6229 3215 0 979340. 63 07. 77 -081. 15 E I 3260 11tbrt twin* 34 9746 18 3826 3260 0 979349. 64 04. 10 -075. 63 F H 3366 1i tbrt twin* 34 9930 18 3380 3366 0 979327 88 08 84 -075. 90 £ H 5712 1itbrt tw i n* 34 9861 18 3717 3712 0 979318 28 09. 61 -075. 40 £ H 3874 1i tbrt twin* 34 9685 18. 3306 3874. 0 979298 73 09 32 -084. 04 E H 3888 1i tbrt twi n* 34 9887 18 6193 3888. 0 979304. 73 16. 71 -071. 34 E H 3919 1 1 tbrt twi n* 34 9349 18 6141 3919. 0 979297 83 14. 67 -075. 76 E H 6413 litbtwn 1i tbrt twin* 34. 9338 18 3724 6413. 0 979238 02 16. 80 -083 93 E H 6340 1i tbrt twin* 34 9558 18. 3964 6540. 0 979255 79 15. 91 -079. 45 E H 6333 1itbrt twin* 34 9303 18 6229 6355 0 979236. 40 24. 47 -087. 24 E BM6674 dioritt 1itbrt twin* 34 9343 18. 6143 6674. 0 979227 27 25 01 -089. 03 0 I 2738 tojavt 33. 0242 18 1848 2758 0 979474 32 01. 17 -107. 63 F I 2766 HOJIVt 33 0093 18 1849 2766 0 979472 24 01. 07 -108. 09 F X 2846 toj«vt 33 0238 18 2027 2846 0 979468. 40 01 13 -108 29 F I 2847 tojavt 33 0093 18 2027 2847 0 979465 12 01 11 -110 32 F X 2886 mo javt 35 0685 18. 1832 2886. 0 979469. 63 01 16 -108 44 F X 2896 mojava 33 0336 18 2026 2896. 0 979466 98 01 27 -109 12 F I 2933 mo ja va 33 0240 18 2203 2933. 0 979460. 39 01. 09 -111. 06 F I 2939 MO javt 33 0369 18 2206 2939. 0 979461. 29 01. 13 -110. 93 F I 2943 MO JJVt 33 0091 18 2204 2943 0 979438 37 01. 09 -111 33 G BM 2933 MO Jt Vt 33. 0809 18 1823 2933 0 979463 58 01 28 -109. 43 F I 3004 mo jtva 33 0684 18 2029 3004. 0 979460. 43 01. 22 -110 30 F I 3038 mo jtva 33 0609 18 2137 3038. 0 979456. 98 01. 23 -111. 28 F I 3036 mo jtva 33. 0317 18 2332 3061. 0 979431. 10 01. 48 -113 08 F 256 I 3062 AC JOV* 35 0339 18 2246 3062 0 979453. 98 01 23 >112 26 F I 3071 •o java 35 0240 18 2203 3071 0 979430. 77 01 07 -112. 37 F I 3130 ao java 35 0644 IB 2203 3130 0 979430. 93 01 29 -112 07 F BM 31 63 ao java 35 1081 18 1880 3163 0 979432. 02 01 63 -112 38 G 1 3 IBS ao java 33 0449 18 2424 3183 0 979444 01 01. 22 -114 14 F I 3302 ao java 35 0340 18 2380 3202 0 979444 93 01 28 -112 92 F I 3216 ao java 35 0717 18. 2204 3216 0 979447 01 01. 30 -111. 49 F I 3306 ao java 35 0644 18 2381 3308 0 979440 79 01 43 — ill. 46 F BM 3312 aojava 33 1144 18 2030 3312. 6 979443 63 02 06 -109. 96 0 I 3333 ao java 35 0734 18 2301 3333 0 979440 63 01 39 -109 89 F BM 3387 ao java 33 1143 18 2138 3387 0 979441. 93 02 75 -108 52 G K 3402 ao java 35 0813 18 2202 3402 0 979436. 93 01. 99 -110 58 E BM 3467 aojava 33 1171 18 2246 3467 0 979438 22 02 86 -107. 37 G I 3337 ao java 33 0713 18 2479 3537 0 979427. 41 01 73 -110. 23 F BM 3308 ao java 33 1086 16 2432 3587 0 979430. 42 03. 69 -106. 66 G 1 3143 ^onolith 33 0090 IB 2339 3143 0 979445 42 01. 04 -112 39 F I 3 3 3 9 ®.©no 1i th 35. 0090 18 2736 3227. 3 979440 83 00. 96 -112 02 F 1 3331 ftonolith 33 0385 18 2338 3231. 0 979435 76 01. 16 -119.17 F I 3278 Aonolith 35. 0092 IB 2915 3278 0 979439. 72 01. 41 -109. 67 F I 3300 Aono1ith 33 0238 18 2734 3300 0 979431 22 01. 17 -118. 33 F I 334S aono1i th 33 0091 18 3094 3345 0 979434. 34 01. 29 -ill 15 F I 3421 aonoli th 35. 0240 18 2913 3421. 0 979429. 08 01. 19 -113. 24 F I 3448 aono1i th 33 0214 18 3094 3448. 0 979432 84 01. 27 -107. 56 F 1 3S41 aono1i th 33 0092 18. 3269 3341. 0 979426. 32 01. 67 -106. 89 F I 3556 Aonoli th 35 0384 IB 2916 3556. 0 979421 69 01. 69 -113. 28 F I 3571 aono1i th 35 0346 18 2998 3371 0 979424. 89 01. 17 -109. 39 F BM 3666 aono1i th 35 1044 18. 2552 3666. 0 979427 06 03 29 -103. 34 G I 3706 aonoli th 35 0371 18. 3117 3706. 0 979421. 95 01. 30 -104. 33 F BM 3770 aono1i th 35 1043 18 2700 3770. 0 979420. 81 04. 96 -103. 70 G 3M 3900 aono1i th 35 0970 18. 2970 3800. 0 979423 46 04. 24 -099. 35 G I 3824 aono1i th 35 0939 18. 3040 3824. 0 979425. 36 03. 75 -096. 40 F 1 3845 aono1i th 35. 0027 18 3439 3843 0 979408 24 02. 32 -103. 81 F BM 3382 aonoli th 35 1021 18. 3120 3882 0 979427. 21 02. 82 -092. 55 G H 3897 aonoli th 33 0610 18. 2734 3894. 0 979405. 35 03. 68 -109 13 E BM 3919 aonoli th 33 1212 18. 3537 3919 0 979424 90 01. 79 -095. 30 G BM 3922 aono1i th 33 1174 18 3369 3921 3 979423. 60 01. 47 -096. 43 G I 3942 aonolith 35 1212 18 3646 3942 0 979424. 19 01. 65 -094. 78 F H 4025 aono1i th 33. 0369 18 2911 4023. 0 979398. 83 03. 09 -108. 28 E H 4202 aono1ith 33 0610 18 3192 4202 O 979394. 96 02. 84 -102. 17 E H 4371 aonolith 33 0369 18. 3377 4371. 0 9793B6. 38 02. 96 -098. 48 £ H 4382 aono1i th 33 0472 18 3429 4382 0 979383 29 03. 68 -099. 07 E H 4398 aono1ith 35 0231 18 3434 4398. 0 979373. 81 07. OO -102. 23 E H 4507 aono1ith 33. 0648 18. 3494 4307. 0 979381 13 03. 61 -097. 32 E H 4623 aono 1 i th 33. 0848 18 2774 4623. 0 979366 23 04. 66 -105. 93 E M 4703 aono1i th 33. 0963 18 2632 4703. 0 979360 28 06. 21 -106. 33 E H 4708 aonolith 33. 0022 18 3624 4708 0 979352 80 07. 01 -104. 92 E BM 4850 paaa aonoli th 35 0777 18 3053 4830 0 979333. 84 04. 80 -104. 00 G H 4858 aono1i th 33. 0846 18 2877 4858. 0 979331. 29 03. 44 -106. 00 E BM 5362 1iaat t aono1i th 33 0106 18 3652 3361. 3 979310 30 11. 28 -104. 78 G wall 33(j1) aono1i th 35 1136 18. 3625 3924 0 979425. 89 01. 47 -093. 69 H BM 3037 naanach school 34. 7831 18 6247 3037. 0 979429. 66 01. 20 -113. 21 G BM 2992 naanach shcool 34. 7831 18. 6068 2990. 5 979432. 31 01. 12 -113 21 G BM 1820 oilar paak 33 2715 18 6242 1820 0 979568. 81 03. 46 -083. 81 G BM 863 pas tor ia cr aa k 34. 9932 18. 8460 863. 0 979615. 04 03. 44 -073. 06 G H 1593 pas tor ia craak 34 9383 18 8351 1393 0 979372 83 08 27 -064. 27 E H 1721 pas tor ia cr aak 34 9882 18 8460 1721. 0 979574. 80 07. 06 -060. 10 E H 1760 pastor ia c r aa k 34. 9389 18. 8205 1760. 0 979364. 36 07. 96 -063. 14 E BM 3028 pastor ia cr aak 34 9019 18. 7829 3207. 9 979477. 51 06. 60 -061. 79 G tajon k pastor ia craak 34 8936 18 7832 3363. 7 979465. 41 06. 99 -063. 66 G H 3597 pas tor la crfak 34 9134 18. 7944 3597 0 979438. 18 09. 78 -033. 67 E H 3673 pas tor ia craak 34 9202 18. 8087 3673. 0 979430. 13 14. 22 -053. 31 E 257 H 3703 pa * toria craak 34 9217 18 8026 3705 0 979461 13 09 32 -047 20 E BM 3783 pat or t a craak 34 9033 18 8400 3785 0 979446 68 09 72 -033 31 0 BM 3873 trap M* or l a craak 34 8934 18 7693 3837 0 979432 33 12 83 -061 20 c K 4080 P«i or i a craak 34 8916 18 8227 4080 0 979427 49 07 38 -037 84 E 1M 4240 law! a pac or ia cr aak 34 8969 IS 7639 4260 0 979406 33 07 18 -069 08 0 H 4378 or ia cr aak 34 9277 18 7332 4378 0 979393 43 09 06 -061 69 E BM 3497 tah chapi n 33 1397 18 4737 3637 0 979446 63 02 64 -091 64 0 BM 3774 tah chapl n 35 1463 18 4705 3774 0 979439 81 02 26 -090 72 G I 3778 tak chap t n 33 1333 18 4939 3778 0 979445 86 01 66 -083 62 F 1 3821 tah chapi n 33 1393 18 4936 3821 0 979443 46 01 63 -083 98 F I 3824 tak c hap1 n 33 1427 18 4938 3824 0 979443 14 01 81 -084 34 F BM 3690 tak chap1 n 33 1407 18 4712 3830 0 979436 38 01 77 -089 61 0 C 3639 tak chapi n 33 1338 18 4848 3833 0 979439 30 02 09 -086 99 F I 3072 tak chap1 n 33 1683 18 4983 3892 0 979439 78 02 03 -083 79 F BM 3879 tak chapi n 33 1330 18 4634 3896 0 979433 71 01. 34 -089 29 G I 3913 tak chapi n 33 1392 18 4866 3915. 0 979435 62 02. 00 -087 84 F C 3917 tak chap1 n 33 1391 18 4830 3917. 0 979433 63 01 68 -086 31 F BM 3928 tah chapi n 33 1343 18 4384 3928 0 979430 09 01 32 -090 93 G H 3932 tah chapi n 33 1712 18 4803 3932 0 979432 37 07 36 -083. 52 E C 3942 tah chapi n 33 1392 18 4488 3942 3 979430. 30 01. 48 -090. 14 F C 3944 tah chapi n 33 1318 18 4668 3946 0 979431 23 01. 37 -088 46 F C 3947 23 tah chapi n 33 1392 18. 4669 3947. 3 979430 34 01. 61 -089. 88 F i n 33 1366 18 4432 3936. 0 979429 30 01. 48 -090 11 G I 3947 tah chapi n 33 1323 18 4481 3967. 4 979427. 63 01. 39 -090. 82 F I 3993 tah chapi n 33 1340 18 4310 3995 0 979428 03 01 52 -088. 98 F BM 4007 tah chapi n 33 1303 18 4313 4007 0 979424. 83 01 48 -091. 19 G I 4010 7 tah chapi n 33 1279 18 4830 4010 7 979430 30 01 87 -084. 91 G BM 4018 tah chapi n 35 1259 18 3997 4018. 0 979423 17 01. 50 -091. 80 G X 4027 (21/22) tah chapi n 33 1263 18 4311 4027 0 979423. 93 01. 66 -090. 37 F I 4027 (24) tah chapi n 33 1280 18 4938 4027. 0 979430. 63 01. 82 -083. 64 F BM 4031 tah chap1 n 33 1278 18 4130 4031. 0 979424 86 01. 36 -089. 43 G H 4048 tah chapi n 33 1379 18 4367 4068. 0 979423 28 01. 97 -087 23 E H 4087 tah chapi n 35 1380 18. 4260 4087. 0 979424. 09 02. 23 -087. 03 E H 4112 tah chapi n 35 1652 18 481 1 4112 0 979421.73 03. 89 -088 57 E H 4143 tah chapi n 33 1734 18. 4948 4145. 0 979422. 26 04 82 -083 83 E H 4180 tah chapi n 33. 1756 18 4889 4180 0 979416. 73 06. 06 -088. 19 E H 4288 tah chapi n 33 1333 18. 4137 4288 0 979410. 93 04. 06 -086 14 E BM 4380 tah chapi n 35. 1336 18. 4083 4380. 0 979404 26 03. 72 -087. 31 G H 4343 tah chapi n 33 1411 18. 4046 4343. 0 979392. 83 04. 33 -089. 00 E wall 43 tah chap1 n 33. 1269 18 4039 4024. 1 979424. 14 01. 33 -090. 30 H wall 44 tah chapi n 33 1264 18 4736 3992 0 979430 03 01 78 -086 24 H BM 4399 »ono tah chap1 na 33 1239 18 3646 4399. 0 979391. 14 04 87 -097. 69 G H 4447 tah chapi na 33 1368 18 3682 4447 0 979386 64 03. 01 -102. 10 E 3M 3983 tah chapi • 33 1227 18. 3779 3983. 0 979423 38 01. 39 -093 32 Q SM 3990 tah chapi • 33 1240 18 3864 3990 0 979423. 61 01. 37 -093. 00 G I 4013 tah chapi a 33 1243 18. 4491 4013. 1 979423. 74 01. 90 -088. 99 F I 4034. 04 tah chapi a 33. 1244 18. 4313 4034. 1 979423. 73 01. 67 -089. 98 F I 4041. 4 tah c hapi a 33 1243 18. 4133 4041. 4 979422. 71 01. 30 -090. 73 F BH 4097 tah chapi « 33. 1242 18. 4832 4037. 0 979427. 96 02. 03 -083 99 G I 4073. 94 tah chap1 a 33. 1168 18. 4493 4074. 0 979423. 34 02. 12 -086 89 F X 4081. 43 tah chap1 a 33 1172 18.4317 4081. 4 979420. 68 01. 78 -089. 49 F BM 4137 tah chapi a 33. 1098 18.4140 4138. 3 979414. 48 01. 36 -091. 86 G X 4143. 36 tah chapi a 33 1097 18 4316 4143. 4 979416. 60 01. 96 -088. 92 F I 4190 33 tah chap1 a 35 1096 18 4492 4180 3 979417 31 02. 29 -085 79 F I 4283 tah chap1 a 33 0933 18 4232 4282. 6 979405. 84 02. 34 -089. 88 F C 4347 tah chapi a 33. 0930 18. 4321 4347 0 979403. 77 02. 34 -087. 88 F H 4339 tah chapi a 33. 0984 18. 4333 4338. 0 979403. 33 02. 78 -087. 70 E BM 4369 tah chap1 a 33. 0942 18.4124 4369. 0 979400. 01 02. 40 -090. 39 G H 4649 tak chap1 a 33. 0832 18. 4228 4645. 0 979384. 39 03. 16 -083. 79 E H 4841 tah chapi a 33 0802 18.4210 4841. 0 979370. 69 03. 44 -089. 23 E H 9006 tah chapi a 33 0332 18 3794 3006. 0 979347. 14 03. 61 -096. 96 E 258 UJ © © © © © © o - o o r> 4 1 9 4 < 0♦ fr r t p s © SP 4 ft rn N fr fr N o fr N 0 o 1 i ? 0 1 1 ? m r t * 4 r* r » H p) O -0 04 r> n P I p » 9 O rt 4 1 O O o H 04 0 4 o 94 pi r> 4 ) N © © m frf r PI p) < 0 Jt ♦ P s r> 9 « rth -r> rt pi pi © rtm rt O - f r o f rf r f r N P sN P >N P s 0“ o O f rf r f r 0 0 O o o o 04 rtp s © oif r fr 9 4 4) $ © 9 r> N 9* © rt ftr>t f t4 14 )N rn r> $ f rrt * * f r fr o o o PI $ o f r fr © f r p» PI ♦ f r * f r © © © © © © * ■ * 9 -4 H 94 o 4 n -*f r f r r> O O I I I I K U. 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* * 4 - C C C C - • - 4 rt rt ^ rt rt rt ,^^^,„«,^_,*_i.-,.-.~..~i~.,4.~i,4~. o o o o OOOOOOOOOOOOOfff fft OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO rt « H r-4 -»-»-»“»-»~»">*>->-»-*-»-»eie®, -»“*“***“»ccceceecccccccccccccccecccccecccccc'rt_**I-i • • • • • • • • • • • • • 3 3 3 0 * l « l « » » 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 r t - r t - r t - r t OOOOOOOOOOOOOOOOOOOC oOOOOOOOOOOOOOOqoO OOOOOOOrtrtrtrtrtrtrtrtrtScifiWttWrtrtrt-H-H-rt-rtTrtrt'NKrt'Hrt^-Mrt^rti* • ■•••■•••••■■••(■•■■•■•ai • ••^.■•.•.•.•.^•.•.^•.•.•••.•.•.•.•.•.•.ikOLXXXXXjexXXXXXXXXXXXXXfcXXXXXXXXXXXXXXXXXX 4*4»4*4»4»4*'*»«»4»4»4»4»4»4»4#4»4«4»4»4l>u4*4»4»4»4***4M>«»4«4»4*4«4»«»+*4»4»4» C CC c c c c c c c C C CC C C C C C C -M 0 0 * m * * * T X. • J 5 5 . J J! ##<M.«HH»4»#W4*4»*.vii*n»4'4*V4»rt6f(ON4n4ftN-Of»S4l3l »ftN4rtNnj4NOOOrtNP)4n4MS01 # « # c m «• # m « m p c p p p ip pi pi p p p ppifii^HH^Hfifi^H^oOOOOOOOOOOOOOOOO^^^^^^^^^^ APPENDIX II. DETAILS OF THE COLLECTION AND REDUCTION GRAVITY DATA. APPENDIX II DETAILS OF THE COLLECTION AND REDUCTION OF GRAVITY DATA A. STATION LOCATIONS Elevation data for transmission line profiles were provided by the Southern California Edison Company. The California Department of Water Resources provided elevation data for stations along the access road. Measurements in and around Bear Valley were made at street monuments, the elevations of which were provided by the Bear Valley Community Services District. Within Tehachapi, Cummings, and Brite Valleys, measurements were made at numerous water wells whose ground elevations were provided by the Tehachapi Cummings Water District. Station elevations for the profiles along Bear Mountain Boulevard, Tehachapi-Bakersfield Highway and Tehachapi-Willow Springs Road were obtained by leveling. Station elevations were determined using an Hewlett-Packard 3810A Total Station Distance Meter. The meter uses an infrared laser and computes the horizontal and vertical distances after correcting for atmospheric curvature of the beam path. Leveling was tied to as many benchmarks as possible and was performed only in a single direction. 263 Measurements at all other locations were made where elevations could be obtained directly from the U. S. Geological Survey topographic map sheets. Such sites included hill tops, road intersections, spot elevations and benchmarks. Measurements at benchmarks were made as close as practical to the mark. However, it was necessary in some cases to make the measurement at a considerable distance if the marker was located in concrete posts, on boulders, or in other unsatisfactory positions. For spot elevations, measurements were made next to stakes, posts, or other indicators of the elevation location, if they were recoverable. When such markers were not found the locations were estimated. Spot elevations generally correspond to an obvious location and the vertical error associated with estimating their position is probably <0.5 m. Elevations from topographic maps fall into two catagories; 1) first, second and third order spirit-level benchmarks and supplemental benchmarks, and 2) spot elevations. Third and higher order spirit-level benchmark elevations are accurate to <0.3 m. Supplemental benchmarks are required to be accurate to within 0.1 contour interval for contour intervals of _<_10 m and within 1 m for larger intervals. Spot elevation accuracy is within 0.3 contour intervals. Contour intervals on the maps covering the survey area ranged from 5 to 50 feet, 20 and 50 foot 264 intervals being the most common. Therefore, the largest elevation errors, those associated with a spot elevation, should be _<_ 2-5 m which would correspond to a gravity error of _<_ 1.5 mgal. Horizontal location accuracy is estimated to be _<_0.02 inch on a 1:24 ,000 map which corresponds to 12 m in the field. North-south horizontal position accuracy is important in the determination of the theoretical gravity whereas east-west errors are relatively unimportant. A north-south error of 100 m in the location of a station corresponds to a 0.08 mgal latitude correction error. B. MEASUREMENTS AND CORRECTIONS Due to the large elevation variation within the study area, 200 to 2500 m, stations were frequently beyond the direct range of the meter from an absolute base. Intermediate base stations were established and subsequently tied to one of the absolute bases. Intermediate bases were also used in areas for efficiency when long distances separated the survey area from an abs olu t e ba s e. At each station two or more gravity meter readings were made and averaged, the mean value being used for that station. Readings were generally within 0.3 dial divisions. A 0.5 dial division uncertainty would correspond to an uncertainty in the gravity of 0.04 mgal. 265 The drift rate was assumed to be linear during the intervals between base station readings. In reality, the drift curve is probably more complicated than a simple linear change. However, in the absence of data to suggest otherwise, a linear drift rate is assumed. The affect of this assumption on the drift corrected gravity values is not known. The observed instrument drift rate varied from day to day but was not obviously correlated with air or instrument temperature, elevation change, road conditions, or other sources. Errors associated with the topographic corrections are a function of the compartment size used in the analysis and the terrain. To reduce the error associated with estimating the average elevation, the number of compartments in zones I, J, and K, was increased to 24 from the 12 typically used. Determination of the average elevation on an evenly sloping or flat surface was more accurate than on a complicated undulating surface. It is difficult to assess the influence of the topographic roughness on the precision of the correction. C. DATA ANALYSIS The matrix used in contouring the data was computed using a polynomial-fitting routine adapted by Fogarty (1985) from Braile (1978). The program calculates a 266 variable order polynomial from data points in a circular sub-region surrounding the grid point. Then, to obtain the value for the grid point, the polynomial is evalutated at that point. Four grid points were calculated from each polynomial. The programs allows the sub-region surrounding the grid point to be expanded depending on the amount of data in the area. If the density of data points is insufficent, the radius of the sub-region is extended until a sufficent number of points are obtained. Additionally, the program considers the distribution of data in each of the four quadrants around the grid point. If too large a percentage of the data is concentrated in one quadrant the sub-region is expanded to include additional data and produce a more uniform distribution of points in each quadrant. The program will calculate polynomials between 3rd and 14th order depending on the number of data points in the sub-region. For specific details of the equations and methods, the reader is referred to Fogarty (1985). In this study, the distribution and density of the data points were such that the gridding routine generally used 3rd or 4th order polynomials. In development of a grid for the entire study area, the sub-region radii varied from 4 to 12 km and included 15 to 80 data points. The density of stations across the survey area varied considerably. In and around the intermontane valleys the 2 data were particularly dense (e.g. 1 station/km ) whereas 267 in more rugged parts of the range data density was very low 2 (e.g. 1 station/10 km ). As a result the grid spacing was varied depending on the area to be contoured. Contour maps of the entire range were produced using 3-4 km grid s paci ngs . The filtering routines use a Fast Fourier Transform (FFT) which assumes an infinite data set. Real data sets, such as gravity maps and profiles, are composed of data which cover a finite area. As a result of the limited data, the ends of the map or profile represent discontinuities. These discontinuities cause oscillations in the Fourier transforms which produce errors in filtering (Fogarty, 1985). To alleviate the affects of these discontinuities the original data set was expanded. Though edge affects still exist, they are confined to the expanded area and will not disturb the original data set. This method alleviates errors within the original data set and does not distort its frequency content (Fogarty, 1985). In these analyses the data matrix has been expanded by reflection. Reflecting a line of N data points results in the first value becoming the N times 2 value, the second value becoming the (N times 2) - 1 value, etc. The result is a matrix which is four times the original. All of the filtering routines are based on converting the gravity matrix into a set of amplitudes over a range of wave numbers using a two dimensional FFT. Filtering is then 268 computed in the frequency domain rather than the spatial domain. Since the gravity field is defined by a matrix rather than a continuous surface, the transform employed is a discrete FFT (Fogarty, 1985). Band-pass filtering allows the isolation of anomalies between a specific set of wave numbers. In this way small- scale features can be resolved by removing the masking due to long-wavelength features. Conversely, noise or small- scale variations can be removed to isolate long-wavelength features. During filtering the mean of the data is removed and set to zero. The result is that the values are relative, extending across zero to comparable positive and negative amplitudes. Removal of the mean from filtered gravity data has the effect of reducing distortion at the map edges resulting from Gibbs phenomena (Bracewell, 1965). In order to isolate anomalies of a specific wave number a box function is employed. Wave numbers to be retained are multiplied by 1, and those to be excluded are multiplied by 0. Thus, when the inverse FFT is applied and the data is transformed back into the spatial domain only those wave numbers of interest are restored. FFT analyses limit the wave number of features which are resolvable. The longest resolvable feature equals the length of the survey area, whereas the smallest feature equals twice the station spacing (the Nyquist wavelength). 269

Asset Metadata

Creator Plescia, Jeffrey B. (author)

Core Title A gravity and magnetic study of the Tehachapi Mountains, California

Contributor Digitized by ProQuest (provenance)

Degree Doctor of Philosophy

Degree Program Geological Sciences

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

Tag geophysics,OAI-PMH Harvest

Language English

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c29-350421

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Identifier DP28573.pdf (filename),usctheses-c29-350421 (legacy record id)

Legacy Identifier DP28573.pdf

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Document Type Dissertation

Rights Plescia, Jeffrey B.

Type texts

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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...

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