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Notice Concerning Copyright Restrictions NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. THE SAN ANDREAS FAULT BETWEEN CARRIZO PLAINS AND TEJON PASS, SOUTHERN CALIFORNIA By John C. Crowell Geological Sciences Department University of California Santa Barbara, CA 93106 ABSTRACT units have been identif ied across the San Andreas - San Gabriel fault The San Andreas fault at its system in Soledad Basin and the sharp bend in the northern Trans- Orocopia - Chocolate Mountain re- verse Ranges-separates very differ- gion, indicating about 300 km ( 180 ent rock terrains. North of the mi ) of right slip. fault basement rocks Consist of granites mainly of Mesozoic age· Emphasis in this paper is upon with Sierra Nevada affinities,· details observable along the San containing included remnants of Andreas fault zone, such,as fault Paleozoic metasediments. To the landforms, fault slices of many west the basement. is composed of ba- rock varieties, crushed rocks, and sic metamorphic rocks that may be upon the striking contrast in rock uplifted portions of ancient ocean- units across the fault zone as a ic crust. The sedimentary section whole. north of the fault begins with the marine Eocene Tejon Formation and INTRODUCTION is succeeded by a nearly complete sequence, including some interca- In approaching the Transverse lated volcanic rocks, up into'the Ranges along the San Andreas fault Pleistocene Series. Many of these from the northwest, the fault zone northern rock units change facies curves eastward into the Big Bend, from continental beds on the east and near Frazier Park has a due east- to deep-water marine facies on the west strike for a distance of about west where they are sharply trun- 6 km ( 4 mi ). The fault then curves cated by the San Andreas fault. gently southeastward across Tejon Pass and continues along the 'south- Southwest of the fault zone Pre- western margin of the Mojave Desert. cambrian gneisses and migmatites, As the fault enters the Big Bend re- gneisses of unknown age, and Meso- gion south of the Temblor Range its zoic granitic rocks of several surface trace climbs in elevation types are exposed. The Paleocene and crosses through basement terrain - Eocene Pattiway Formation and mid- in the Mount Pinos - San Emigdio Tertiary nonmarine beds and vol- Mountain - Frazier Mountain region canic units in the Caliente Range ( Figs. 1, 2 ). The Big Bend region and Cuyama Valley area are truncat- is also notable for the intersection ed on the northeast by the San An- of other major faults with the San dreas. Mid-Miocene and younger con- Andreas fault: the Garlock, Big glomerates and sandstones in the Pine, San Gabriel, and Liebre, for northern Transverse Ranges were de- example. Despite the conspicuous posited in intermontane valleys pattern of the Big Bend region on with sources to the northeast. A- geologic maps, the evolution and sig- cross the San Andreas fault in that nif icance of this complex area is direction no suitable source areas still unclear and much additional occur today. Suitable source areas investigation is needed. for these beds and counterparts to many of the southern basement-rock Rock units contrast markedly 223 CALIFORNIA DIVISION OF MINES AND GEOLOGY across the San Andreas fault zone in ment rocks is composed of quartz this region. Basement rocks as well monzonite, quartz diorite, and dio- as overlying sedimentary sections rite, and constitutes the upper cannot be correlated directly across plate of the north branch of the the fault zone. Some matching se- Garlock fault. This major tectonic quences have been recognized out- movement zone, marked by mylonite side of the Big Bend region and and blastomylonite, is exposed in provide evidence for many miles of the Neenach Quadrangle ( Wiese, right slip on the San Andreas fault 1950; Peters, 1972 ) and dips to the system, including the San Gabriel north at about 50 degrees. It over- fault ( Hill and Dibblee, 1953; lies tectonically Pelona Schist, a Crowell, 1962, 1968, this volume; greenschist-facies sequence of pro- Wiebe, 1970; Ross, 1972; Huffman, bable Mesozoic age reconstituted 1972; Matthews, 1973 ). from graywacke, mudstone, some chert, carbonate rocks, and volcan- In the Carrizo Plains area on ic rocks ( Ehlig, this volume ). At the northwest sedimentary facies the eastern border of the Lebec contrast strongly across the fault Quadrangle, this north-dipping ma- ( Vedder, this volume ) and many jor fault is truncated by the south- fault landforms are well displayed dipping Pastoria thrust ( Crowell, ( Wallace, 1968; this volume ). To 1952 ), another major fault. The the southeast of Tejon Pass, part Pastoria thrust in turn is truncated of the thick sedimentary section on the south by the south branch of within Ridge Basin ( Crowell, this the Garlock fault, no doubt the volume ) is juxtaposed against principal strike-slip branch of the an eastward-thickening sequence of Garlock. Rocks in the upper plate very different sedimentary and vol- of the Pastoria thrust, and consti- canic strata. These units lying tuting the long ridge surmounted by north of the fault include the Tecuya Mountain and Santa Emigdio Neenach volcanic rocks and Miocene Mountain, consist mainly of gray sedimentary formations ( Wiese, 1950; granodiorite and quartz monzonite Crowell, 1952; Dibblee, 1967; with inclusions of marble and horn- Matthews, 1973 ). The fault zone fels. These Paleozoic (?) meta- itself through the. Big Bend region sedimentary rocks are best preserved is marked by scarps, sagponds, off- in roof pendants south of the Gar- set streams, and other fault land- lock fault; here, the limestone beds forms lying within a broad, con- have been intruded by coarse pink spicuous fault trough. The trough granite, quartz monzonite, and is primarily the result of long granodiorite. Basement-rock types erosion in fault-shattered rocks. cropping out in the westernmost This article is primarily concerned San Emigdio Mountains consist of with features within and along this gabbro, pyroxenite, hornblende quartz fault zone on a route followed by diorite, quartz gabbro, amphibolite, public roads. and metadiabase ( Hammond, 1958; Ross, 1970, 1972 ). These mafic and ROCK UNITS NORTH OF THE SAN ANDREAS ultramaf ic rocks may originally have FAULT been of suboceanic origin, whereas most of the eastern granitic rocks Basement rocks within the San north of the San Andreas fault Emigdio Mountains and southwestern appear similar to those of the south- part of the Tehachapi Mountains con- ern Sierra Nevada. Unfortunately, sist mainly of gneiss, schist, except for local studies, this sec- granitic and gabbroic rocks of sev- tor of basement rocks has not as yet eral types, and metasedimentary been investigated or mapped in rocks. Part of this strip of base- detail. 224 CALIFORNIA DIVISION OF MINES AND GEOLOGY Sedimentary rocks lying unconfor- ROCK UNITS SOUTH OF THE SAN ANDREAS mably upon this basement terrain FAULT consist of a thick section of marine and nonmarine beds extending stra- Basement rocks south of the San tigraphically upward from the Eo- Andreas fault in the region of the cene Tejon Formation. On the west, Big Bend consist of various types beds of this Tertiary sequence are of gneiss, schist, and granitics. entirely marine up through the Plio- Work by Silver (1971) on lead- cene, but, eastward, the section uranium isotopes shows that blue- changes facies rapidly; Oligocene quartz bearing layered gneiss of and Miocene units, for example, are Frazier Mountain are between 1750 replaced laterally by nonmarine and 1680 m.y. in age, and were conglomerates ( Nilsen and others, intruded by porphyritic granodiorite 1973 )· During early and mid- and quartz monzonite between 1650 Tertiary times, prisms of sediments and 1680 m.y. ago. The latter rocks, with mainly north-south facies now consisting of distinctive augen trends were laid down facing the gneisses, were metamorphosed about sea on the west; these beds are now 1425-1450 m.y. ago, and then intrud- upturned as the result of the ele- ed by gabbro, diorite, and minor vation of the San Emigdio - Teha- anorthosite about 1220 m.y. ago. chapi Mountains in Pleistocene These definitely Precambiran rocks time. The outcrop secti.on in map are best viewed on Frazier Mountain view today in the foothills dis- ( Fig. 2, locality 23 ), and along plays a sequence passing from con- Lockwood and Piru Creeks. Other tinental beds on the east into multiple deformed gneisses, not yet deep-water marine deposits on the dated isotopically, are well exposed west ( e.9-., Hammond, 1958; Nilsen, along the roads to the tops of Mt. 1973; Nilsen and others, 1973 ). Abel ( Fig. 1, locality 9 ) and to Mt. These marine units reach to the Pinos ( Fig. 2 ). Granitic rocks of San Andreas fault in the Temblor several types and ages also occur Range ( Vedder, this volume ), and in the region ( e.9-., Crowell, 1964; in the northern part of the San Carman, 1964; Lofgren, 1967; Evern- Andreas sector described in this den and Kistler, 1970; Ross, 1972 ).
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