CALVIN H. STEVENS Department of Geology, California State University, San Jose, California 95114 ROBERT C. OLSON Humble Oil and Refining Co., P. O. Box 2180, Houston, Texas 77001

Nature and Significance of the Inyo

Thrust Fault, Eastern California

ABSTRACT INTRODUCTION A major thrust fault, here called the Inyo Large-scale thrust faulting in southeastern thrust fault, appears to extend under the California has been recognized for at least two northern Inyo and southern White Mountains. decades, but not until 1966 were the ubiquity The allochthon consists of late Precambrian to of these structures and the probable magnitude Late Ordovician rock near exposures of the of movement realized (Stewart and others, thrust fault, but elsewhere rock as young as 1966). Stewart and others suggested that Pennsylvanian or Permian is exposed. Missis- various thrust-fault segments exposed in the sippian rock generally underlies the fault. region, including the east side of the Inyo Chert in the allochthon shows no trace of Mountains (Fig. 1), were all part of one fault original structure within many tens of feet of which they named the Last Chance thrust the fault surface, but carbonate rock overlying fault. They and Stevens (1969) suggested that the tault shows only a thin zone of brecciation the thrust fault on the east side of the Inyo and shearing. Overturned folds in the region Mountains probably extended under the north- and offset of Mississippian facies suggest cast- ern Inyo and southern White Mountains be- ward movement of the allochthon which con- cause rocks in this upper plate, called the Inyo- tains continuous stratigraphic units for 17 mi White Mountains allochthon by Stevens across and 55 mi along the mountains. It ap- (1970), are structurally coherent. pears, therefore, that at least an 800-sq-mi Olson (1970) discovered that in the noith- block in the northern Inyo and southern White west flank of the Inyo Mountains older rock Mountains has moved a minimum of 17 mi overlies younger rock along about 5 mi of eastward along the Inyo thrust fault. The Last almost continuous exposure (Fig. 2). This low- Chance allochthon to the east may have been angle fault was named the Inyo thrust fault by derived from the Inyo-White Mountains al- him and that name is used here to designate lochthon and parts of it may have travelled the surface under the Inyo-White Mountains an additional 20 mi or more eastward. The allochthon. The Last Chance thrust fault Harkless Flat allochthon, now preserved on underlies an allochthon or allochthons here the western flank of the Inyo Mountains, called the Last Chance allochthon. probably has travelled 5 or 6 mi westward from place of origin in the Inyo-White Mountains GENERAL STRATIGRAPHIC allochthon. INTERPRETATIONS Movement of the Inyo-White Mountains Late Precambrian to Permian rock crops and Last Chance allochthons, and probably out in the immediate area of the Inyo thrust the Harkless Flat allochthon, ceased before fault (Fig. 2). Rock in the allochthon ranges Middle Jurassic and probably prior to Early in age from late Precambrian to at least Late Jurassic, as plutons at least 165 m.y. old have Ordovician near the fault, but rock as young not been offset by the thrust faults. These as Pennsylvanian or Early Permian occurs folds and thrust faults in the Inyo and White several miles to the southeast. Farther south- Mountains form part of a probable Tnassic east, Late Permian and Early Triassic sedi- tectonic belt postulated by Burchfiel and mentary rock and post-Early Triassic volcanic- others (1970) to extend from southeastern rock crop out, but these are autochthonous California to Idaho. relative to the Invo-Whitc Mountains al-

Geological Society of America Bulletin, v. 83, p. 3761-3768, 5 figs., December 1972 3761

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lochthon (Stevens, 1970). In the autochthon, Mississippian through Permian rock has been recognized with the possibility that both younger and older rock could be present, Wlrtvws throuh although not identifiable. In the allochthon, Lail Chcilc* ThrMSI rock ranging in age from Middle Cambrian to at least Late Ordovician is cut by the fault, but under the Inyo Mountains, Precambrian sedimentary rock also must lie on the fault surface. The thrust fault at one place or an- other cuts all of the rock exposed in the autoch- thon, although generally the Mississippian Perdido Formation immediately underlies the fault. ALLOCHTHON The following units have been mapped by Olson (1970) in the allochthon in the imme- diate vicinity of the Inyo thrust fault on the west flank of the Inyo Mountains: Ordovician: Al Rose Formation and Badger Flat Limestone (Mazourka Group), Ely Springs Dolomite; Cambrian: Saline Valley Formation, Mule Spring Limestone, Monola Formation, Bo- Figure 1. Location map (modified after Stewart and nanza King Dolomite, Tamarack Canyon Dolo- others, 1966). mite; Precambrian: Reed Dolomite. Folds occur throughout the allochthon along the west flank of the Inyo Mountains 9 mi, probably have had considerable move- from the latitude of Tinemaha Reservoir ment on them, but the amount has been impos- (Olson, 1970) southward almost to the southern sible to determine. The transverse faults have border of the Independence quadrangle. Most had small amounts of movement on them of the folds in the Independence quadrangle (Olson, 1970) and apparently reflect adjust- are almost isoclinal and show eastward ment between longitudinal faults. The longi- vergence. The axial planes, however, dip tudinal faults dip westward at moderate angles steeply. Folds range in wave length from and are thought to be reversed, based on several inches to 600 ft or more except for the orientation of small tight folds overturned to Mazourka Canyon syncline (Fig. 1), the wave the east and drag folds. These faults probably length of which is several miles. The west were formed during events that led up to the flank of this large fold is locally overturned major thrust-faulting episode or were formed (Olson, 1970; Ridley, 1971), thus also showing concurrently with early phases of thrust eastward vergence. In general, the smallest faulting. folds appear to represent drag on the larger A second series of possible preintrusive folds and they in turn are drag features on the longitudinal faults occurs near Tinemaha Res- limbs of the Mazourka Canyon syncline. ervoir. One of these faults intersects the Inyo At least two tectonic events have produced thrust fault under a small patch of alluvial faulting in the allochthon. First, several faults cover at 12 (Fig. 2). This fault is believed to in the Independence quadrangle are truncated terminate against the thrust fault because of by small stocks of granitic rock (Olson, 1970) lack of offset of the thrust zone. Apparent associated with the Santa Rita Flat pluton of normal movement and lack of penetration of Middle Jurassic age (Ross, 1969). Other faults this fault into the autochthon suggest that with similar trends and similar types of move- it may be a pull-apart structure at the back ment have been assigned to this group. Both of the allochthon similar to several shown longitudinal and transverse faults represent diagrammatically by Kehle (1970). this preintrusive tectonic episode. The longi- Faults cutting the Santa Rita Flat pluton tudinal faults, which have been traced up to along the Waucoba Mountain-Independence

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quadrangle boundary (Olson, 1970) dip west- chert embedded in a maze of silica veins. ward and show normal movement. They are Farther away from the fault, randomly oriented thought to belong to the episode of Cenozoic blocks of various sizes with well-preserved bed- Basin and Range faulting that produced the ding have been cemented together by silica. adjacent Owens Valley (Olson, 1970). Still farther from the fault contact, chert beds are intact. AUTOCHTHON The fault trace is in the form of a series of Rock exposed below the Inyo thrust fault loops, as the fault is involved in a series of on the west flank of the Inyo Mountains have north-trending folds. Near 2 (Fig. 2), all bed- been assigned to the following units: Mississip- ding apparently dips eastward, showing that pian: Perdido Formation, Rest Spring Shale; the east limb of the synform is lacking here. Pennsylvanian to Permian: Keeler Canyon We interpret this to mean that these structures Formation; Permian: Owens Valley Forma- have been both folded and jammed into the tion. Only a few tight folds (as at 8, Fig. 2) autochthonous rock units during and perhaps with wave lengths of 300 to 400 ft have been after thrusting. East of the synform (east of 2, recognized in the autochthon, but this may Fig. 2) a small, beautifully exposed antiform be due to the difficulty of delineating struc- has been breached by erosion exposing Missis- tures in units composed primarily of bkck sippian rock in the center. At 10 (Fig. 2), in a shale. These folds appear to be overturned to second antiform, Mississippian rock in the the east and to plunge gently southward. autochthon is exposed in a northward-pointing Faulting in the autochthon seems to be finger, providing the best exposures of the important only in isolated hill 1 (Fig. 2). Inyo thrust fault in the area. Black chert (totally brecciated to well bedded) Although the structure of hill 1 (Fig. 2) is on the highest point of this hill is identical to very complex and incompletely understood, rock assigned to the Ely Springs Dolomite(?), it appears that a synform overturned to the a quarter of a mile to the east, so the fault east and involving the Inyo thrust fault occu- under this chert is considered to be part of pies the highest point. Along the easternmost the Inyo thrust fault. Other important faults exposures of the autochthon, as at 11 (Fig. 2), on this hill, conceivably ramps up which or the Inyo thrust fault apparently dips between parallel to which the Inyo-White Mountains 25° and 40° east. allochthon was pushed onto the low-angle Inyo thrust fault, are reverse and dip westward REGIONAL INTERPRETATIONS at angles of about 35°. Cross sections A and B The Inyo thrust fault underlies northern (Fig. 2) show the interpreted structure. Inyo and southern White Mountains. Apparent continuity of the Precambrian- INYO THRUST FAULT ZONE Paleozoic sequence in the Inyo and White Shearing and brecciation, and folding of Mountains, as shown by Ross (1967a), suggests the allochthon into the autochthon (Fig. 2, that the main part of these mountains is com- cross sections C, D) are features associated posed of a single structural block—the Inyo- with the fault zone. Shearing in the Mississip- White Mountains allochthon. This block has pian rock at the top of the autochthon com- been highly faulted (Nelson, 1966, 1971), but monly is intense, but limited to within a few the over-all form at the ktitude of Tinemaha feet of the contact. Where dolomite marks the Reservoir is that of an enormous anticline base of the allochthon a zone of granulated (Fig- 3). carbonate rock only a few feet thick generally We consider that the thrust faults exposed marks the contact, but near 11 (Fig. 2), injec- on the east and west sides of the Inyo Moun- tions of black shale from the autochthon are tains are the same surface for several reasons: seen to extend several tens of feet into the (1) on both sides of the Inyo Mountains rock upper plate. Where black chert marks the of the coherent Inyo-White Mountains al- base of the allochthon, total destruction of lochthon rests upon equivalent Mississippian original structures commonly extends many units; (2) the presumed same thrust fault can tens of feet from the contact. Where no orig- be inferred to have been exposed prior to inal structures in the chert have been pre- massive intrusion at the northern margin of served near the thrust fault contact, the rock the allochthon where it appears to separate typically consists of small fragments of black Precambrian and Cambrian miogeosynclinal

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cal movement. Possibly the east-west-trending anticlines and synclines in the allochthon do not involve the thrust fault. Finally, even though the westward limit of carbonate rock in the Perdido Formation in the allochthon follows a northeast-trending line, which if extended to the latitude of Tinemaha Reser- voir, lies at least 9 mi east of the reservoir, perhaps this line swings abruptly westward near the southern border of the Waucoba Mountain quadrangle. It seems unlikely to us, however, that all these possibilities could be true. The Inyo thrust fault also is postulated to have been present throughout the White Mountains before being almost totally obliter- ated during great intrusive episodes. Here, probable early Mesozoic metavolcanic rocks are nearly encircled by Precambrian through Ordovician rock (Crowder and Ross, 1972, Fig. 1), suggesting that the younger sequence represents a large window through the Inyo thrust fault. The only preserved fault contact Figure 4. Major folds in the northern Inyo and between these very different rock sequences, southern White Mountains (based upon geology of near Pellisier Creek, dips about 45° westward, the Inyo-White Mountains allochthon and elevation with the older rock overlying younger. of the Inyo thrust fault). Primary and Secondary Allochthons Delineation of the Inyo-White Mountains rock from probable early Mesozoic rock allochthon is based upon structural continuity (Crowder and Sheridan, 1972), and at the of rock units. Thus, all of the Precambrian and southern edge where the Inyo-White Moun- Cambrian units of the northern Inyo Moun- tains allochthon lies over a projection of the tains eastward to an important structural dis- Cerro Gordo anticline (Fig. 1); (3) the alloch- continuity on the east side of the Inyo Moun- thon and the fault surface apparently have tains is included in the Inyo-White Mountains been folded into a series of intersecting north- allochthon. This structural discontinuity con- south and east-west-trending structures (Fig. sists of a major fault in the Jackass Flats area 4) so that the autochthon is exposed near Big on the west side of which the margin of the Pine and at Jackass Flats because these areas Inyo-White Mountains allochthon is bent lie near the crest of one east-west-trending down and turned under (Fig. 3). This structure antiform; (4) folds in the autochthon, alloch- extends about 8 mi southward along Jackass thon, and the fault itself all suggest similar Flats and then swings westward across the eastward movement of the Inyo-White Moun- Inyo Mountains (Nelson, 1971; Ross, 1965, tains allochthon; and (5) limestone beds in the 1967b). Rock to the east of the discontinuity, Perdido Formation in the autochthon occur at here referred to as the Last Chance allochthon, least 9 mi west of their expected position, based is intensely disturbed only along this zone in upon study of facies of the Perdido Formation the area of the Jackass Flats window (Stewart in the allochthon in the Independence quad- and others, 1966), where it apparently has rangle (Ridley, 1971). been pushed up and overturned to the east Alternate interpretations of some of these (Fig. 3). The Last Chance allochthon lies on lines of evidence could be made. Proximity of the same surface (Mississippian black shale for Precambrian rock and probable Mesozoic meta- the most part) as the Inyo-White Mountains volcanic rock in the White Mountains con- allochthon, but the two are interpreted here to ceivably could be due to several miles of verti- be different allochthons with different histo-

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ries. To avoid confusion, we employ the name Springs Dolomite(P) extends about 700 ft east "Last Chance thrust fault" (Stewart and of known Ely Springs Dolomite outcrops. Evi- others, 1966) to designate the surface under dently, the Ely Springs Dolomite was first the Last Chance allochthon and Inyo thrust moved many miles eastward along with the fault for that under the Inyo-White Mountains remainder of the Inyo-White Mountains al- allochthon. The Last Chance allochthon could lochthon and later experienced hundreds of represent a secondary sheet or probably several feet of westward movement. The sequential sheets that detached during emplacement of development of these structures is shown dia- the primary Inyo-White Mountains allochthon grammatically in Figure 5. and moved eastward ahead of the primary allochthon (Fig. 5). Significantly, rock exposed Amount of Movement in the Last Chance allochthon had been present Offset of Mississippian facies indicates mini- in the Inyo-White Mountains allochthon at mum movement of 9 mi, and the distance across much higher elevations (Fig. 3). Johnson the Inyo Mountains from westernmost to east- (1971) has differentiated multiple superim- ernmost outcrops of the allochthon indicates a posed thrust sheets in the Cottonwood Moun- minimum movement of 17 mi. The position of tains southeast of the Inyo Mountains, a struc- the Last Chance allochthon (Fig. 3) indicates tural situation unlike that in the Inyo and that the western edge of this allochthon prob- White Mountains, but consistent with our ably travelled about 9 mi eastward beyond the hypothesis of one primary and multiple second- eastern margin of the Inyo-White Mountains ary allochthons. An alternative explanation allochthon. The Last Chance allochthon that the major allochthons are one (Stewart stretches 20 mi beyond the margin of the and others, 1966) seems less probable to us. Inyo-White Mountains allochthon, however, During latter stages of movement the major implying that either an original 11-mi-wide allochthons squeezed together, producing the frontal portion as well as the 9-mi-wide upper structures now visible in the vicinity of Jackass part of the Inyo-White Mountains allochthon Flats. disengaged together to form the Last Chance Tectonic denudation of the Inyo-White allochthon, or that low-angle faulting resulting Mountains allochthon also produced sheets in attenuation within the Last Chance alloch- that moved westward opposite the direction of thon has allowed the eastern parts of it to movement of the primary allochthon. These move 11 mi farther eastward than the western allochthons are represented by several small parts. The amount of eastward movement in masses of Cambrian rock and a 15-sq-mi rem- either case requires that some of the allochthon- nant of Precambrian rock mapped east of ous rock of the White and Inyo Mountains Tinemaha Reservoir by Nelson (1966). This originated at least as far west as the crest of the mass of Precambrian rock, here called the Sierra Nevada where today Mesozoic plutons Harkless Flat allochthon, appears to rest on and Mesozoic and Paleozoic sedimentary rock Cambrian rock along a low-angle fault (Fig. (Rinehart and Ross, 1964), that apparently are 3), a point concurred with by Nelson (oral of somewhat different lithologies than those in commun., 1971). Westward movement on the Inyo and White Mountains, are exposed. the Harkless Flat allochthon is postulated This seems to indicate that at least part of the because appropriate units had been present pre-furassic sedimentary rock in the eastern higher in the Inyo-White Mountains alloch- Sierra Nevada was thrust faulted in from still thon to the east (Fig. 3) and westward vergence farther west. in the relatively autochthonous Cambrian rock The Harkless Flat allochthon probably never and in some of the late Paleozoic rock of the was very large. Its position on the west flank autochthon is shown along the western margin of the Inyo Mountains requires 5 or 6 mi of of this allochthon (Nelson, 1966; Olson, 1970). westward movement. Westward movement of the Harkless Flat al- lochthon, postdating original thrusting, also Time of Movement resulted in a small amount of reverse movement The Inyo-White Mountains allochthon has on the Inyo thrust fault. A measure of west- been intruded extensively in a post-thrust ward movement on the earlier thrust fault is faulting episode recognized by Evernden and indicated at 9 (Fig. 2), where a band of Ely Kistler (1970) as Early and Middle Jurassic

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K-X:^ CAMBRIAN THROUGH DEVONIAN ROCKS

PRECAMBRIAN ROCKS

Figure 5. Interpreted sequence of events in devel- Harkless Flat allochthons. opment of Inyo-White Mountains, Last Chance, and

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(160 to 180 m.y.). Burchfiel and others (1970) ing the enormous fold from which the major have summarized similar ages for plutons far- part of the modern Inyo and White Mountains ther east that penetrate the Last Chance alloch- are formed (most of the reverse faults and thon and cut the Last Chance thrust fault. isoclinal folds in the Inyo-White Mountains Thus, the time of major thrust faulting must allochthon probably formed at this time); (2) have been Early Jurassic at the latest. eastward movement of the primary allochthon, In the immediate area of the Inyo thrust possibly up faults parallel to those observed fault, the youngest deformed rock is Permian. dipping 35° to 45° to the west onto the low- Southeastward, however, in the New York angle Inyo thrust fault. This probable Middle Butte quadrangle, structures similar to those Triassic event seemingly was intensely com- at Tinemaha Reservoir (John Kelley, unpub. pressional; (3) breakaway of the Inyo-White manuscript) undoubtedly formed during the Mountains and Last Chance allochthons in same tectonic event, involve post-Early Tri- Middle Triassic (beginning of gravity move- assic volcanic rock. Thus, emplacement of the ment) ; (4) termination of eastward movement Inyo-White Mountains and Last Chance al- by the end of the Triassic; (5) beginning of lochthons seemingly must have been either massive intrusion of granitic plutons in Early Middle or Late Triassic or earliest Jurassic. Jurassic, perhaps coincident with westward Evernden and Kistler (1970) have recognized movement of the Harkless Flat and related an early intrusive epoch of Middle and Late allochthons. Triassic age (210 to 195 m.y.) in the Lee Vining area about 70 mi north of Tinemaha Reservoir ACKNOWLEDGMENTS that may predate thrusting, and McKee and We greatly appreciate the long-term interest Nash (1967) obtained a similar age of 213 m.y. and conversations with D. C. Ross (U.S. in a small mass on the north side of Deep Geological Survey) concerning many phases Spring Valley (Fig. 1). of this work. We are also grateful to R. L. Time of emplacement of the Harkless alloch- Rose and Scott Creely (Department of Geol- thon is uncertain. Silicification of breccia along ogy, California State University, San Jose), and the Inyo thrust fault after westward movement J. H. Stewart (U.S. Geological Survey) lor has been complete, however, and a series of their comments and help with the manuscript. minor intrusions, probably related to the Conversations with C. A. Nelson (University of Papoose Flat pluton (Nelson, 1966) occurs California, Los Angeles) also were very helpful. both in the relatively autochthonous rock and John Nakata and Peter Galanis prepared the in the Harkless Flat allochthon (Nelson, 1966). figures, and Janice Meadows typed the man- The Papoose Flat pluton has given K-Ar ages uscript. of 75 and 81 m.y. (Kistler and others, 1965), suggesting that the Harkless Flat allochthon REFERENCES CITED was emplaced during the Mcsozoic. Nelson Burchfiel, B. C., Pelton, P. J., and Sutler, J., 1970, (1966) shows one small stock cut by a fault of An early Mesozoic deformation belt in south- undetermined dip at the edge of the Harkless central Nevada-southeastern California: Geol. Flat allochthon, but this may reflect movement Soc. America Bull., v. 81, p. 211-215. Crowder, D. F., and Ross, D. C., 1972, Permian(?) at a later period. to Jurassic(P) metavolcanic and related rocks SUMMARY that mark a major structural break in the northern White Mountains, California-Ne- Low-angle laulting in the Inyo and White vada: U.S. Geol. Survey Prof. Paper 800-B, Mountains in southeastern California repre- p. B195-203. sents part of a tectonic belt postulated by Crowder, D. P., and Sheridan, M. P., 1972, Geo- Burchfiel and others (1970) to extend from logic map of the White Mountain Peak quad- southern California to Idaho. The age is thought rangle, Mono County, California: U.S. Gcol. Survey Map GQ-1012 (in press). by them to be Early Jurassic or Late Triassic, Evernden/T. P., and Kistler, R. W., 1970, Chro- but it may be older. The sequence and timing nology of emplacement of Mesozoic batholithic of events associated with this orogeny and complexes in California and western Nevada: particularly formation of the Inyo thrust fault U.S. Geol. Survey Prof. Paper 623, 42 p. are interpreted as: (1) compression from the Johnson, E. A., 1971, Thrust laulting in the eastern west, probably in the Middle Triassic, form- Cottonwood Mountains, Death Valley, Cali-

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fornia: Geol. Soc. America, Abs. with Pro- Ross, D. C., 1965, Geology of the Independence grams (Cordilleran Sec.), v. 3, no. 2, p. 141. quadrangle, Inyo County, California: U.S. Kehle, R. O., 1970, Analysis of gravity sliding and Geol. Survey Bull. 1181-0, p. 01-064. orogenic translation: Geol. Soc. America Bull., 1967a, Generalized geologic map of the Inyo v. 81, p. 1641-1664. Mountains region, California: U.S. Geol. Sur- Kistler, R. W., Bateman, P. C., and Brannock, vey Misc. Geol. Inv. Map 1-506, 1:125,000. W. W., 1965, Isotopic ages of minerals from 1967b, Geologic map of the Waucoba Wash granitic rocks of the central Sierra Nevada and quadrangle, Inyo County, California: U.S. Inyo Mountains, California: U.S. Geol. Survey Geol. Survey Map GQ-612, 1:62,500. Prof. Paper 601, 47 p. 1969, Descriptive petrography of three large McKee, E. H., and Nash, D. B., 1967, Potassium- granitic bodies in the Inyo Mountains, Cali- argon ages of granitic rocks in the Inyo Batho- fornia: U.S. Geol. Survey Prof. Paper 601, lith, east-central California: Geol. Soc. Amer- 47 p. ica Bull., v. 78, p. 669-680. Stevens, C. H., 1969, Middle to Late Triassic de- Nelson, C. A., 1966, Geologic map of the Waucoba formation in the Inyo, White, and northern Mountain quadrangle, Inyo County, Cali- Argus Mountains, California: Geol. Soc. fornia: U.S. Geol. Survey Map GQ-528, America, Abs. with Programs (Rocky Moun- 1:62,500. tain Sec.), pt. 5, p. 78. 1971, Geologic map of the Waucoba Spring 1970, Geometry of the Inyo-White Moun- quadrangle, Inyo County, California: U.S. tains allochthon, eastern California [abs.]: Am. Geol. Survey Map GQ-921, 1:62,500. Assoc. Petroleum Geologists Bull., v. 54, Olson, R. C., 1970, Geology of the northwestern p. 872. Inyo Mountains, Inyo County, California Stewart, J. H., Ross, D. C., Nelson, C. A., and [M.S. thesis]: San Jose, San Jose State College, Burchfiel, B. C., 1966, Last Chance Thrust-a 73 p. major fault in the eastern part of Inyo County, Ridley, A. P., 1971, Devonian and Mississippian California: U.S. Geol. Survey Prof. Paper sedimentation and stratigraphy of the Ma- 550-D, p. D23-D34. zourka Canyon area, Inyo Mountains, Inyo County, California [M.S. thesis]: San Jose, San Jose State College, 78 p. Rinehart, C. D., and Ross, D. C., 1964, Geology and mineral deposits of the Mount Morrison MANUSCRIPT RECEIVED BY THE SOCIETY NOVEMBER quadrangle, Sierra Nevada, California: U.S. 22, 1971 Geol. Survey Prof. Paper 385, 106 p. REVISED MANUSCRIPT RECEIVED APRIL 17, 1972

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