U.S. DEPARTMENT OF THE INTERIOR MISCELLANEOUS FIELD STUDIES MF–2344 U.S. GEOLOGICAL SURVEY Sheet 1 of 2 116°00´ 45´ 30´ 15´ 115°00´ 34°30´ A 45 34°30´ Qoa 40 Qoa INTRODUCTION steep west stratal dips of early Miocene rocks in the western Calumet Mountains and is suggested also John, B.E., 1981, Reconnaissance study of Mesozoic plutonic rocks in the Mojave Desert region, in L Qpsh ts Ks Tdvc u Qps YXg 75 Qya d Amboy Crater lava flow Kl 35 by the moderate NNE dip of the early Miocene East Bullion dike swarm in the eastern Bullion Moun- Howard, K.A., Carr, M.D., and Miller, D.M., eds., Tectonic framework of the Mojave and Sonoran 25 l 35 80 Ko Geologic map units are described briefly on this map, with the expectation that readers seeking L Td o 14 Xf Ks u w Painted Rock tains. Cross section A–A' interprets extensional structural style between these localities. Gently east- Deserts, California and Arizona: U.S. Geological Survey Open-file Report 81–503, p. 48–50. Jbv? Tab Qpsg Qya 30 detailed descriptions (including contact relations and modal mineral proportions for plutonic units) can d F Qba l a Qpb 153m Pluton dipping extensional faults are exposed in the eastern Sheep Hole and Pinto Mountains and imaged seis- Karish, C.R., Miller, E.L., and Sutter, J.F., 1987, Mesozoic tectonic and magmatic history of the central o Jbv? 80 u 10 Dၤm Ko 70 consult the source geologic maps listed on the index map (fig. 1). Summary modal diagrams are shown w Jbv? l t 45 PMb Ks mically below Ward Valley (Frost and Okaya, 1986). In cross section A–A', I infer a style of concealed Mojave Desert, in Dickinson, W.R. and Klute, M.A., eds., Mesozoic rocks of southern Arizona and F Qoa e 20 Qya here in Figure 2. Geophysical maps and interpretations are available in Simpson and others (1984), Tblc a Jbv? Tdi a u s 25 70 half grabens under the valleys to be consistent with unmigrated industry seismic reflection profiles adjacent areas: Arizona Geological Society Digest, v. 18, p. 15–32. t 12 30 25 Mariano and others (1986), Frost and Okaya (1986), Mariano and Grauch (1988), and Jachens and l Tdv 16 t b 45 60 (D.A. Okaya, unpub. data). Kupfer, D.H., and Bassett, A.M., 1962, Geologic reconnaissance map of part of the southeastern r Ship Mountains 20 ၤt 20 30 Howard (1992). Neumann and Leszcykowski (1993) summarized information on mines and mineral w Td Qya Ko Tc a 307m 20 45 45 a 65 e 35 n Qps 537m Qya Pluton Ks deposits. Discussions and interpretations of the geology are available from the source geologic maps In late Neogene and Quaternary time, strike-slip faults that are part of the eastern California shear Mojave Desert, California: U.S. Geological Survey Mineral Investigations Field Studies Map Tbl s Qoa c Qoa Xf Dၤm 10 50 20 50 t h 5 Kl 40 zone displaced rocks in western parts of the quadrangle (Howard and Miller, 1992; Richard, 1993). MF–205, scale 1:125,000. b 20 80 55 25 and elsewhere, and are briefly summarized here. The map was prepared in 1994. r 15 30 35 65 30 YXg 50 East-striking faults (in the Pinto Mountains) are sinistral, and NW-striking faults are dextral (Dibblee, Lucchitta, Ivo, 1979, Late Cenozoic uplift of the Colorado Plateau and adjacent Colorado River region: a Tdi Qoa 15 Xk Ko Qo n Jsm 40 20 NAMES Qoa c 70 1961, 1967a; Hope, 1966; Jagiello, 1991). Ranges and basins in the quadrangle may owe their forms Tectonophysics, v. 61, p.63–95. h 13 247m 40 Qya Qpb 0 30 40 The map applies new names to structures including the Ivanhoe fault, eastern Bullion dike swarm, 60 25 15 largely to transpression and transtension between the moving and rotating strike-slip fault blocks Luyendyk, B.P., 1991, A model for Neogene crustal rotations, transtension, and transpression in south- 307m t 45 5 Old Woman Pluton Ko Qblc s 30 Amboy Crater lava flow, Ship Mountains pluton, Cleghorn Pass pluton, Sheep Hole Mountains pluton, (Simpson and others, 1984; Jagiello and others, 1992; Jachens and Howard, 1992; Richard, 1993). ern California: Geological Society of America Bulletin, v. 103, p. 1528–1536. ru ts 55 th Qya 50 Ko a Xk and Sheep Hole Pass pluton. I apply pluton names to structural bodies and not necessarily to lithodemes Large rotations are expected between the Pinto and Bullion Mountains based on models of bookshelf Mariano, John, and Grauch, V.J.S., 1988, Aeromagnetic maps of the Colorado River region including D m Xk Qya Tdv 8 ၤ 50 Ks ts or map units, even though they may largely coincide. For example, the Old Woman pluton is an intru- Qpsh faulting and regional paleomagnetic studies (Carter and others, 1987; Luyendyk, 1991; Dokka and the Kingman, Needles, Salton Sea, and El Centro 1° x 2° quadrangles, California, Arizona, and Qya 45 10 897m 25 a sive body consisting of the formally named Old Woman Mountains Granodiorite. Map units newly Travis, 1990; Richard, 1993). However, Jurassic dike swarms in these two ranges have unexpectedly Nevada: U.S. Geological Survey Miscellaneous Field Studies Map MF–2023, 3 sheets, scale 20 20 Tc Km 35 Xk 40 40 named on this map are the Dale Lake Volcanics; Coxcomb Intrusive Suite and its included Sheep Hole similar strikes, a finding that may accord better with small relative rotation (approximately 20°) pre- 1:250,000. 50 70 Jd Tbst Qoa 60 45 60 Pass Granite, Sheep Hole Mountains Granodiorite, and Clarks Pass Granodiorite; Iron Mountains Intru- dicted by Powell's (1993) palinspastic model. Mariano, John, Helferty, M.G., and Gage, T.B., 1986, Bouguer and isostatic residual gravity maps of 80 89 n 30 50 a Qbl 30 Qoa Qy lo 80 n ၤt sive Suite and its included Granite Pass Granite, Danby Lake Granite Gneiss, and Iron Granodiorite A slickensided surface was encountered in drilling of probable Quaternary deposits under Cadiz the Colorado River region, including the Kingman, Needles, Salton Sea, and El Centro 1° x 2° a 50 60 Qoa 10 c Xk Kop Qy Ycm S 50 Gneiss; Chubbuck Porphyry; Bullion Mountains Intrusive Suite and its included Virginia Dale Quartz Lake (Bassett and others, 1959; Howard and Miller, 1992). The presence of this concealed fault sug- quadrangles: U.S. Geological Survey Open-file Report 86–347, scale 1:250,000, 7 sheets. Qoa Qya Xk Qya Monzonite; and Dog Wash Gneiss. Intrusive suites are proposed on this map in order to group together gests that other Quaternary faults could be concealed by the widespread Holocene deposits in Bristol Metzger, D.G., 1968, The Bouse Formation (Pliocene) of the Parker–Blythe–Cibola area, Arizona and Qy ၦm 75 KJpg 80 85 each of a series of lithodemes that appear to be closely related lithologically, spatially, and temporally. Lake, Cadiz, and Danby Lake valleys. Faults exposed in the east and central parts of the quadrangle last California: Geological Survey Research, 1968, U.S.Geological Survey Professional Paper 600–D, Qoa Jd 85 80 50 Qbl 45 Ycm Ycm 9 Ko 60 Ko The underlying concept of an intrusive suite is that all the units are in some manner cogenetic and that moved in the early Pleistocene, whereas the Valley Mountain faults in the southwest part of the quad- p. 126–136. Qoa Td ts 65 55 6055 101m Dၤm ၤt they are products of a single fusion episode (Bateman, 1992). Qoa rangle cut deposits assigned to the Holocene (Howard and Miller, 1992). This concentration of young- Miller, C.D., 1989, Potential hazards from future volcanic eruptions in California: U.S. Geological Sur- 75 45 30 est fault activity to the southwest accords with a southwestward increase in seismicity (Goter, 1992). vey Bulletin 1847, 17 p. Jbv? 60 45 Xs GEOLOGIC SUMMARY Jbv 70 Ycm Km Miller, C.F., Howard, K.A., and Hoisch, T.D., 1982, Mesozoic thrusting, metamorphism, and pluton- Ko 40 C 80 PMb 60 The Sheep Hole Mountains quadrangle covers an area of the Mojave Desert characterized by ism, Old Woman-Piute Range, southeastern California, in Frost, E.G. and Martin, D.L, eds., Meso- l e Kcg Qya gh Qya Ko basins and ranges (fig. 3). Alluviated valleys and playas (dry lakes) are as low as 165 m elevation at zoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada Qpsg Jd Ko REFERENCES CITED o Jbv? Qoa 75 Cadiz Lake playa (see map of major topographic features). The mountain ranges they separate are as Jbv r 45 20 Anderson, J.L., 1988, Core complexes of the Mojave-Sonoran Desert: Conditions of plutonism, myloni- (Anderson-Hamilton volume): San Diego, Cordilleran Publishers, p. 1561–581 Jbv n Qps Qwo Qoa 35 50 50 high as 1490 m elevation, for example in the Old Woman Mountains. Rock units are well exposed P 60 Ko ts tization, and decompression, in Ernst, W.G., ed., Metamorphism and crustal evolution of the west- Miller, C.F., Wooden, J.L., Bennett, V.C., Wright, J.E., Solomon, G.C., and Hurst, R.W., 1990, Petro- Qoa a Qwy Kcg 70 Km Km s Ko 55 owing to low rainfall and sparse vegetation. genesis of the composite peraluminous-metaluminous Old Woman-Piute Range batholith, south- s 85 Qwy ern United States (Rubey volume 7): Englewood Cliffs, New Jersey, Prentice Hall, p. 502–525. Jbpm ts 50 F Qoa 75 80 Ko eastern California; Isotopic constraints, in Anderson, J.L., ed., The nature and origin of Cordilleran a Kccp? 40 Ko Kop PROTEROZOIC ROCKS Bacheller, John, III, 1978, Quaternary geology of the Mojave Desert-Eastern Transverse Ranges boun- u 50 80 Kcg 80 45 35 35 l Kcsh 20 70 70 magmatism: Geological Society of America Memoir 174, p.