U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP 1-2389 U.S. GEOLOGICAL SURVEY BEDROCK GEOLOGIC MAP OF THE EL PASO MOUNTAINS IN THE GARLOCK AND EL PASO PEAKS 7-1/2' QUADRANGLES, KERN COUNTY, CALIFORNIA By Michael D. Carr, Robert L. Christiansen, Forrest G. Poole, and John W. Goodge GEOLOGIC SETTING 1973; Carr and others, 1984) quartz diorite to quartz monzodiorite pluton, also unaffected by any ductile The El Paso Mountains are a range of mountain peaks deformation, intrudes the metasedimentary and met­ trending east-northeast along the north side of the avolcanic rocks in the easternmost El Paso Mountains. Garlock Fault, approximately 25 km southwest of the city of Ridgecrest in eastern Kern County, California. The stratigraphy and structure of the Paleozoic The south flank of the range is structurally controlled metasedimentary and metavolcanic marine strata in the by the left-lateral Garlock Fault and descends abruptly eastern part of the El Paso Mountains are the focus .into Fremont Valley, an alluvial basin with a closed of this study. Hess (1909) and Hulin (1925) briefly drainage system that terminates in Koehn Lake playa described these rocks, and Hess (1909, p. 30) reported (see fig. 1). Numerous surficial features that indicate two poorly preserved fossils from the eastern part of youthful activity along the left-lateral Garlock Fault are the metamorphic rock assemblage as probably no younger present along the south edge of the mountain range than Carboniferous in age. Dibblee (1952, 1967) (Clark, 1973). The north flank of the range slopes mapped the central part of the El Paso Mountains at more gently and is bordered by a tableland terrain a scale of 1:62,500 and formally divided the meta­ underlain by gently dipping Tertiary sedimentary and sedimentary and metavolcanic rocks into the now­ volcanic strata (Dibblee, 1952; Cox and Diggles, 1986). abandoned Mesquite Schist and the now-abandoned Numerous narrow canyons dissect these tablelands. Most Garlock Formation (see Carr and others, 1984). Dibblee of these canyons drain northward and westward into (1952) subdivided the Garlock Series (later renamed Indian Wells Valley, but several prominent drainages the Garlock Formation by Dibblee, 1967) into twenty­ cut southward through deeply incised canyons that cross two members and reported Permian fusulinids near the the axis of the El Paso Mountains, exposing the pre­ middle part (his Member 12) of the formation. Tertiary metamorphic and plutonic rocks that form the Christiansen (1961) mapped the El Paso Mountains core of the range. The west end of the El Paso Mountains from Red Rock Canyon eastward to the longitude of is separated from the south end of the Sierra Nevada the village of Garlock at a scale of 1:24,000; his mapping by low hills west of Red Rock Canyon; eastward the of the area now covered by the Garlock 7 .5-minute El Paso Mountains merge into a hilly terrain under­ quadrangle forms a partial basis for this compilation. lain by Mesozoic granitic rocks. Poole and others (1977, 1980) and Poole and Most of the west half of the El Paso Mountains (west Christiansen ( 1980) reported the results of additional of Mesquite Canyon) is underlain by an intrusive suite fossil discoveries from the western (structurally lower) of Late Permian and Early Triassic age (table 1; ap­ part of the Garlock Formation, demonstrating the pendix 1; Cox and Morton, 1980; Carr and others, presence of Ordovician and Devonian rocks in the 1984) ranging in composition from gabbro to granite formation. Poole (197 4) also tentatively correlated rocks (Dibblee, 1952; Christiansen, 1961). [Note: Geologic near the middle part of the Garlock Formation with ages in this report are based on the time scale of Palmer, Mississippian rocks of the Antler foreland basin of 1983; ages cited from the literature have been con­ Nevada. Building on this previous work, the remain­ verted as necessary to conform to decay constants rec­ der of the present compilation is based on 1:24,000- ommended by Steiger and Jager, 1977.] Immediately scale geologic mapping and stratigraphic studies done west of Mesquite Canyon, the Late Permian gneiss of between 1979 and 1982. The preliminary findings Weiss Mountain and numerous smaller bodies of fo­ of this study were presented by Carr and others (1980, liated felsic and mafic Late Permian intrusive rocks intrude 1984) and include the results of additional fossil dis­ the diverse assemblage of Paleozoic metasedimentary coveries throughout much of the Garlock Formation. and metavolcanic marine strata that underlies most of The metasedimentary and metavolcanic marine strata the east half of the El Paso Mountains. The Permian of the El Paso Mountains represent nearly every system intrusive rocks are gneissic, having a penetrative fo­ of the Paleozoic Era. There is no direct fossil evidence liation that is coplanar with the foliation in the meta­ for the Silurian, but Silurian to Early Devonian fossils morphic rocks to the east. The Triassic plutons that have been recovered from generally correlative rock intrude the gneiss of Weiss Mountain on the west are sequences exposed in Pilot Knob Valley, about 50 km undeformed; their intrusion postdates the ductile east of the El Paso Mountains, and some Silurian rocks deformation that affected the older rocks (Christiansen, could be present in the El Paso Mountains as well {Carr 1961). A Late Jurassic (table 2; Armstrong and Suppe, and others, 1992). 1 117"45' Naval Air Weapons Station . Ridgecrest IChina Lake 35"30' 35"15' EXPlANATION Sierra Nevada Sierra Nevada batholith Surficial deposits (Quaternary) Metasedimentary rocks Sedimentary and volcanic deposits (fertiary) Rand Mountains El Paso Mountains Granitoid pluton Granitoid pluton (Jurassic) Rand Schist Granitoid pluton \friassic and Permian) Johannesburg Gneiss of Hulin (1925) Bond Buyer sequence 33' Garlock assemblage Contact AREA OF MAP Fault-Dashed where inferred or approximately located; dotted where concealed Figure 1. Generalized geologic map of El Paso Mountains and surrounding area. Modified from Jennings and others (1962) and Carr and others (1984). 2 Two distinct sequences of Upper Cambrian and Ordo­ correlated the rocks comprising the Apache Mine unit vician rocks are present in the El Paso Mountains section. with Mississippian rocks in the Great Basin interpreted Upper Cambrian and Ordovician strata in the Garlock as foreland basin deposits shed from the Antler oro­ 7. 5-minute quadrangle (metasedimentary rocks of Colo­ genic highland. He interpreted the basal (western) contact rado Camp) are mostly meta-argillite and argillitic of these rocks (metasedimentary rocks of Apache Mine) metachert belonging to an outer continental-margin facies. as a faulted unconformity (see Poole, 197 4, Carr and Upper Cambrian and Ordovician rocks in the El Paso others, 1980). Peaks 7 .5-minute quadrangle (metasedimentary rocks The Pennsylvanian strata (metasedimentary rocks of of El Paso Peaks) are lithologically more diverse, including Benson Well) that conformably overlie the meta-sedi­ meta-argillite, marble (detrital metalimestone), graptolitic mentary· rocks of Apache Mine also are a turbidite slate, and orthoquartzite. These rocks represent facies sequence (slate and quartzite member). In the El Paso transitional between the outer and inner continental Peaks quadrangle, however, metalimestone representing margin. a shallower water environment forms the basal mem­ The Devonian rocks in the Garlock and parts of the ber (metalimestone member) of the metasedimentary El Paso Peaks quadrangles (metasedimentary rocks of rocks of Benson Well, and the Pennsylvanian section Gerbracht Camp) also represent outer continental-margin rests unconformably on rocks of inferred Devonian age. facies. The metasedimentary rocks of Gerbracht Camp The metalimestone member of the Benson Well unit comprise a sequence of metachert, metatuff, sandy marble grades upward into a sequence of very fine grained (detrital metalimestone), and meta-argillite with fine­ turbidites (slate and quartzite member), suggesting basin grained quartzite (distal turbidites). Greenstone that subsidence. we tentatively assign to the Devonian and infer to lie West of Mormon Flat, Permian strata (metasedimen­ stratigraphically below the metasedimentary rocks of tary rocks of Holland Camp, in part) rest unconform­ Gerbracht Camp is present, as well, in both the Garlock ably on Upper Cambrian or Lower Ordovician rocks. and El Paso Peaks quadrangles. Calcsilicate hornfels There, the lowermost part (member A) of the Permi­ and subordinate marble mapped as the upper mem­ an section is a lithologically heterogeneous unit of slate ber of the metasedimentary rocks of El Paso Peaks could containing beds of arkosic quartzite, metaconglomerate, also be, in part, Silurian(?) and Devonian(?) judging from metadolostone, and metalimestone. The quartzite, meta­ their apparent stratigraphic position. These rocks, like conglomerate, and beds of metamorphosed carbonate the lower members of the metasedimentary rocks of rocks are mostly debris-flow and turbidite deposits. Early El Paso Peaks, probably represent a facies transitional Permian fusulinids are present in the lower part of the between the outer and inner continental margin. section. Member B is slate containing turbidite beds Lower Mississippian rocks assigned to the Robbers of coarse-grained calcarenitic metalimestone. East of Mountain Formation (Carr and others, 1992) rest un­ Goler Gulch, most of the Permian section consists of