Nature and Significance of the Inyo Thrust Fault, Eastern California: Discussion and Reply

Nature and significance of the Inyo thrust fault, eastern California: Discussion and reply

Discussion

GEORGE C. DUNNE Department of Geosciences, California State University, Northridge, Northridge, California 91324 RACHEL M. GULLIVER Envicom Corporation, 4521 Sherman Oaks Avenue, Sherman Oaks, California 91403

INTRODUCTION Olson (1972, Fig. 2). Also included in Fig- caught between two downward-convergent ure 1 are our alternative interpretations of faults, one of which truncates the other; Stevens and Olson (1972) proposed that the geology along their cross-section lines. folding is observed in one area, but it seems a complexly faulted area at the west base of We base our interpretations on 11 days of to result from drag along one of the faults. the northern Inyo Mountains is a window field work in the Tinemaha area. Locations 2, 3: The elongate mass of Or- in a folded, large-slip fault they named the We have few disagreements with the dovician chert and an adjacent elongate ex- Inyo thrust fault. On the basis of their rec- more objective aspects of the geologic posure of Mississippian rock are essentially ognition of this window and earlier struc- mapping of Stevens and Olson. We agree in homoclinal, separated by steep faults that tural interpretations by Stevens (1969, general with their identification and map dip toward the younger sequence (see cross 1970), Stevens and Olson proposed a distribution of rock units, although we sus- section C, Fig. 1). Location 5: The tectonic model in which the Inyo thrust pect that some units on hills 1 and 4 (Fig. 1) arrowhead-shaped contact between older fault played a major role in the Mesozoic are misidentified. We also agree that the and younger sequences is shaped by two structural evolution of eastern California. Ordovician-Cambrian rock sequence is sets of steeply dipping faults, one set having We developed an interest in the work of everywhere in fault contact with the a northeast trend, the other a northwest Stevens and Olson for two reasons. First, Permian-Mississippian sequence. trend. Location 6: Two "klippen" of Or- we were intrigued by the contrast between We disagree, however, with the major in- dovician rock are brecciated near their the map and cross sections of the proposed terpretive aspect of Stevens and Olson's bases, and we interpret them to be landslide window by Stevens and Olson and mapping mapping of the Tinemaha area. They con- blocks; the underlying Mississippian se- of the same area by Nelson (1966), who tended that the faulted contact between the quence is poorly exposed and appears to be showed the structure to be dominated by Ordovician-Cambrian sequence and the homoclinal (no evidence for a large syn- normal faulting. Second, and more impor- Permian-Mississippian sequence is a tightly form). Location 7: An older rock sequence tant, the tectonic model of Stevens and Ol- folded thrust fault that separates older appears to rest upon a younger rock se- son, which relies heavily on their interpre- allochthonous units above from younger quence across a flat-lying movement sur- tation of the proposed window, differs autochthonous units below. We believe that face; the older rock mass contains numer- markedly from previous tectonic interpre- many field relationships in the Tinemaha ous brecciated zones, including contact tations of this part of eastern California area cannot be readily reconciled with this with the underlying sequence; we interpret (Stewart and others, 1966). If correct, the thrust-fault hypothesis and that most field the older rock mass to be an old landslide Stevens and Olson model would place im- data are supportive of an alternate model deposit, emplaced from steep slopes (per- portant constraints upon interpretations of that closely follows the earlier work of Nel- haps a fault scarp) to the east. Location 9: the tectonic evolution of this part of the son (1966) — that is, principal structures in The west-trending contact between the Cordilleran orogen. This regional implica- the Tinemaha area have been shaped by older and younger sequences is controlled tion prompted this discussion. normal faulting and subsidiary landsliding. by a set of subvertical, N80°W-trending We comment briefly below on what may faults. Location 10: The north-pointing re- GEOLOGY OF THE be observed (or reasonably inferred where entrant in the contact is controlled by two TINEMAHA AREA exposures are poor) at the major outcrops sets of steep faults having different north- of this faulted contact. Locations are shown ward trends. Locations 11, 12: A faulted Figure 1 is a simplified version of the in Figure 1. contact dips 75°W to 75°E. Locality II: The geological map and cross sections of the Locality I: The fault contact is poorly ex- fault contact is poorly exposed and seems to Tinemaha area presented by Stevens and posed, but the approximate trace of contact have a near-vertical dip. Locality III: The relative to topography suggests it dips fault contact is well exposed at one point and dips 72°SW. Locality IV: The fault is The article discussed was published in the steeply westward. Location 1: The Bulletin, v. 83, p. 3761-3768. "klippe" of Ordovician chert is a wedge well exposed at one point and dips 75°SW.;

Geological Society of America Bulletin, v. 89, p. 1787-1792, 3 figs., December 1978, Doc. no. 81212.

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the relation of fault trace to topography with the interpretation of Stevens and (fan folds), an unusual fold style not ob- suggests a southwest dip along this whole Olson that depicts these older sequences served in mesoscopic folds of this area, stretch. lying in the troughs of synforms, unless it finally, we carefully examined all areas Faults and folds in the Tinemaha area could be shown that these inferred folds where Stevens and Olson contended that have several chara«eristics that are perti- have been tightened past isoclinal geometry the distribution of older and younger rock nent to the interpretation of their origin. First, neither the style nor the attitude of faults separating older and younger rock sequences is consistent with the folded Quaternary units thrust model of Stevens and Olson. Almost unconformity all of the faults juxtaposing older and younger rock sequences display brittle deformation characteristics, notably abun- Permo-Penn. units, undiv. dant brecciation. This predominantly brittle behavior is difficult to reconcile with the model of Stevens and Olson, which postu- lates that this fault developed beneath an allochthon many kilometres thick. Such a Mississippian units,undiv. tectonic setting would favor the develop- unconformity ment of high confining pressure that would in turn promote ductile deformation features such as abundant tight folds, foliation, Ordovician Ely Springs Dolomite and flowage in rocks adjacent to the fault — phenomena that are almost universal for rocks adjacent to major thrust faults in eastern California. We believe that abundant brecciation adjacent to faults in the our irnterpretation« J/ Ordovician, Cambrian units, undiv. Tinemaha area reflects their environment of contact formation, namely relatively low effective east-west high-angle fault confining pressure and/or high strain rate, cross sections of^ conditions characteristic of normal faults Stevens,Olsoiv-t,^ \ V V 7" and landslide slip surfaces. unnamed reverse, thrust fault The attitudes of faults between older and younger rock sequences also are more com- north end, hill Inyo thrust fault

patible with origins as normal faults than as — a tightly folded thrust fault. We measured antiform, anticline the dip of the faulted contact separating older and younger rock sequences at 17 points over the entire Tinemaha area. The synform,syncline south end, hill lowest dip recorded was 40°; the mean dip is 69° and the median dip is 67°. The fault was nowhere observed to dip 25° to 40° east along its eastern exposures as suggested by Stevens and Olson. We think it is more than coincidence that the mean and median dips between pts. 2,3 for these faults are reasonably representa- tive of dips of normal faults in the Great Basin. The pattern of dip direction of these Figure 1. Slightly simplified faults also is more consistent with the nor- between pts. 5,6 version of geologic map and mal fault model than with the folded cross sections of Tinemaha thrust-fault interpretation. In areas where area by Stevens and Olson elongate masses of older rocks are bounded (1972) and our alternative in- on both sides by younger rocks, as at loca- ! terpretations of geology along tions 2, 3, and 5, faults bounding the older y their cross-section lines. Loca- rock mass consistently dip in opposite di- tions 1 through 12 on map are rections away from the older rock sequence / those of Stevens and Olson; (for example, see our cross section C, Fig. r->>3 0 m|le te localities I through IV are de- 1). This observation is difficult to reconcile 0 km '/2 scribed in our discussion.

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sequences is controlled by large tight folds stratigraphic trend, it is likely that in the folded and cleaved rocks of Cambrian to (locations 1, 2, 3, 5, 6, 10). Study of at- Tinemaha area Mississippian strata were Permian age which had one or more uncon- titudes of bedding, bedding-cleavage rela- deposited unconformably directly upon formities between Mississippian and Or- tions, and repetition (or lack thereof) of Ordovician rocks, or that the two were dovician units. The general westward dip recognizable sequences of beds fail to sub- separated at most by 100 to 200 m of and the folds and cleavage were the result of stantiate and in most cases clearly disprove Squares Tunnel beds. compressional deformations that affected the existence of the large folds shown by the White and Inyo Mountains region in Stevens and Olson. Map patterns similar to AN ALTERNATIVE MODEL FOR Mesozoic time (Sylvester and Babcock, large fold noses (as at locations 5 and 10) THE TINEMAHA AREA 1975; Dunne and Gulliver, 1976). As ex- are created by the intersection of sets of tensional tectonism developed, this rock se- steeply dipping faults with differing north- Structural features observed in outcrop in quence was cut by one or more west- erly trends. the Tinemaha area combined with the re- dipping normal faults (Fig. 2, a) of moder- gional geologic characteristics discussed ate slip (a few hundred to several hundred REGIONAL GEOLOGIC above provide evidence for an alternative metres). The newly created scarps generated CHARACTERISTICS model for the structural evolution of the landslides composed of Ordovician rock Tinemaha area. This model is illustrated in that moved downhill onto Mississippian Three aspects of the general geology of Figure 2 by a sequence of schematic cross units (Fig. 2, b). Ongoing extension created the northwestern flank of the Inyo Moun- sections. more normal faults (sympathetic and an- tains are pertinent to our interpretation of Before the onset of extensional tectonics tithetic) of moderate slip, juxtaposing Or- the structural evolution of the Tinemaha in late Cenozoic time, the area probably dovician and locally Cambrian rock against area. First, the west face of the Inyo Moun- consisted of predominantly west-dipping Mississippian units (Fig. 2, c). Further tains is an eroded fault-line scarp created by landsliding occurred before the area was major normal faults that separate the Inyo eroded to its present topography (Fig. 2, d). Mountains from Owens Valley to the west WEST EAST Our proposed model has three advan- (Pakiser and others, 1964). At the latitude tages over the model of Stevens and Olson. of Tinemaha a large number of generally First, this alternative model is much more north- to northwest-trending normal faults consistent with structural evidence that may cut the west flank of the Inyo Mountains be observed in outcrop in the Tinemaha (Nelson, 1966; Olson, 1970). Most dip area. Phenomena such as the brittle style westward and are down-to-basin faults and consistently high dip of faults that sympathetic to master normal faults at the separate older from younger rock sequences west base of the range; a few normal faults and the predominance of homoclinal sec- dip eastward and thus are antithetic to the tions across exposures of the Ordovician- principal faults. Cambrian sequence are in accord with our A second important geologic characteris- alternative model. Second, this alternative tic is the combination of very steep slopes model is consistent with the abundant evi- (typical gradient of 400 m/km) and the pre- dence of the important role played by ex- dominant westward dip of bedding. To- tensional tectonics in the evolution of the gether, these conditions have fostered the northwestern Inyo Mountains. Third, this development of numerous landslides, nine alternative model adheres to the Principle of of which were mapped by Nelson (1966) Parsimony (Occam's Razor): because the and Olson (1970) within or just east (up- stratigraphic throw of faults separating the slope) of the Tinemaha area. Ordovician-Cambrian sequence from Mis- A third important feature of the region is sissippian strata is at most a few hundred the northward decrease in the thickness of metres, it is simpler to envision these faults strata separating Mississippian and Or- as having accommodated modest amounts dovician rocks along the length of the Inyo of normal slip rather than tens of kilometres Range. In the Independence quadrangle, of thrust movement. immediately south of the Tinemaha area, Mississippian rocks rest unconformably on REGIONAL THRUST-FAULT progressively older rocks as the contact is MODELS traced northward (Ross, 1965). In the northernmost exposures of this unconfor- Stewart and others (1966) recognized mity, Mississippian and Ordovician rocks that much of the upper Precambrian are separated only by thin, discontinuous Figure 2. Sequence of schematic cross through middle Paleozoic rock from the slivers of Silurian rock and approximately sections illustrating our interpretation of east side of the Inyo Mountains eastward to 100 m of bedded chert (Squares Tunnel general characteristics of structural evolu- the vicinity of the California-Nevada bor- beds) of uncertain Late Devonian or Early tion of Tinemaha area (see text for discus- der was allochthonous, having been thrust Mississippian age (Ridley, 1971). Given this sion). eastward on predominantly Mississippian

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strata during Mesozoic time. The major been exposed prior to massive intrusion at formed during regional, east-vergent fold- thrust fault carrying these rocks eastward, the northern margin of the allochthon ing episodes known to have affected the named the Last Chance thrust by Stewart where it appears to separate Precambrian White and Inyo Mountains during Meso- and others, was recognized in several win- and Cambrian miogeosynclinal rock from zoic time (Sylvester and Babcock, 1975). dows, the westernmost of which is at Jack- probable early Mesozoic rock . . ." (p. 5. Stevens and Olson stated (p. 3764) ass Flats, approximately 25 km east of the 3763). In order to correlate the thrust fault that limestone beds in the Mississippian Tinemaha area (see Fig. 1 of Stevens and in the White Mountains (see Stevens and Perdido Formation at Tinemaha occur 9 mi Olson, 1972). Stewart and others (1966) Olson, 1972, Fig. 1) with the thrust fault at (14 km) west of their expected position as suggested that the Last Chance thrust fault Jackass Flats and the postulated thrust at projected from exposures of Perdido For- probably extends westward beneath much Tinemaha, Stevens and Olson were forced mation in Mazourka Canyon, 12 km south of the Inyo and White Mountains. Stevens to extend the trace of the eastern edge of the of Tinemaha, thus implying that this latter and Olson (1972), on the basis mostly of Inyo thrust plate almost 65 km northward area must have moved relatively eastward their contention that the Tinemaha area from Jackass Flats through terrain contain- as part of the Inyo allochthon. We have represents a window in a major thrust fault, ing no evidence known to us that would studied the original work (Ridley, 1971) substantially modified the model of Stewart suggest the presence of such a major thrust upon which this statement is based, and we and others (1966) by proposing that the fault. Over much of this distance the thrust conclude that available evidence permits a Tinemaha and Jackass Flats windows ex- is projected through large post-thrust in- broad range of interpretations of the loca- pose another thrust fault, which they trusions and beneath broad expanses of tion, orientation, and shape of the fades named the Inyo thrust fault. Stevens and Cenozoic units. Where the fault trace has line to which they refer. This facies line, Olson maintained that it is the Inyo thrust been projected through terrain with exten- which separates limestone-bearing from fault that underlies much of the White and sive Cambrian and late Precambrian expo- limestone-free facies of the Perdido Forma- Inyo Mountains and that the Last Chance sures, stratigraphers familiar with the area tion, is anchored at only two points in thrust plate is a huge gravity-glide block have found no stratigraphic evidence there Mazourka Canyon. At the southern anchor derived from the elevated back of the Inyo (such as disrupted fades trends or abrupt point the distribution of outcrops of thrust plate. changes in thickness) to indicate the pres- limestone-free Perdido Formation permits If our contention that the structural geol- ence of a major-slip thrust fault (C. A. Nel- considerable leeway in locating the facies ogy of the Tinemaha area was shaped prin- son and J. N. Moore, 1977, personal com- line. At the northern anchor point, lime- cipally by normal faulting and subsidiary muns.). stone occurs in the Perdido Formation well landsliding rather than by thrust faulting is 3. "The allochthon and the fault surface within what is shown to be the limestone- correct, then a major premise of the tectonic apparently have been folded into a series of free facies (Ridley, 1971, PI. 1), which model of Stevens and Olson is negated. The intersecting north-south— and east-west— suggests that the facies line could be moved other major premise of the tectonic model trending structures so that the autochthon several kilometres westward at that lat- of Stevens and Olson is correlation of the is exposed near Big Pine (Tinemaha area) itude. This latter change would give the proposed thrust fault at Tinemaha with and at Jackass Flats because these areas lie fades line a northwest trend that would thrust faults exposed at Jackass Flats and in near the crest of one east-west-trending project northward to the vianity of the the White Mountains. This correlation is antiform" (p. 3764). The east-trending an- Tinemaha area, such that occurrence of needed in order to demonstrate the regional tiform shown by Stevens and Olson (their either limestone-bearing or limestone-free extent of their postulated allochthon. Ste- Fig. 4) is at best poorly defined; it has little facies of the Perdido could be expected vens and Olson cited five lines of evidence closure along its western half and is there. In addition, we note that deformation in support of this interpretation. We quote nonexistent near Jackass Flats. Cenozoic other than eastward thrusting of the or paraphrase and then comment upon normal faults probably have exerted the Mazourka Canyon section relative to the each. principal control on the present structural Tinemaha area could account for some relative westward displacement of the facies 1. "On both sides of the Inyo Mountains elevation of the Tinemaha and Jackass Flats line at Tinemaha if such displacement ac- rock of the coherent Inyo-White Mountains areas. Thus, the fact that these two areas tually exists. Especially important in this allochthon (Inyo thrust plate) rests upon are currently exposed at approximately the regard are the abundant normal faults on equivalent Mississippian units" (p. 3763). same elevation is not a substantive basis for the west flank of the Inyo Range at the Several different thrust faults in eastern correlating structures from one area to the latitude of Tinemaha. These faults have had California rest on similar upper Mississip- other. the effect of moving rocks at the west base pian units, principally because the shaley 4. "Folds in the allochthon, autochthon, of the Inyo Range near Tinemaha farther and silty lithologies in such units are and thrust fault itself all suggest similar west relative to the remainder of the range. mechanically favorable sites for detachment eastward movement of the Inyo-White and slippage. Thus, the occurrence of these Mountains allochthon" (p. 3764). We agree units beneath isolated exposures of thrust that east-vergent folds are present in the CONCLUSIONS faults is not a substantial basis for correla- Tinemaha area, although not where shown tion of those fault segments. Moreover, the in Figure 2 of Stevens and Olson. Instead, We believe that the Inyo thrust fault does mere presence of clastic Mississippian units these folds are scattered throughout the not exist. The preponderance of field evi- in a structurally deformed area is not proof area rather than being concentrated near dence as well as the general geologic setting of the presence of a thrust fault. the proposed thrust, which suggests that the suggest that the geology of the Tinemaha 2. "The presumed same thrust fault folds are not directly related to a specific area, postulated by Stevens and Olson to be [Inyo thrust fault] can be inferred to have fault surface. These folds almost certainly the type area of the Inyo thrust fault, was

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instead shaped by normal faulting and sub- tribution of allochthonous rocks in eastern helpful comments on an early version of sidiary landsliding. Correlation of thrust California at the latitude of the Tinemaha this manuscript and Eugene Fritsche and faults exposed at Jackass Flats and in the area. Allan Gutstadt for reviewing a later version. White Mountains with the Tinemaha area We thank Cal Stevens for guiding us also lacks substantive support. We suggest ACKNOWLEDGMENTS through parts of the Tinemaha area and for that within the limits of available data, the numerous lively discussions concerning the tectonic model of Stewart and others (1966) We thank Clark Burchfiel, Johnnie geology of that area. adequately describes the origin and dis- Moore, Clem Nelson, and Art Sylvester for

CALVIN H. STEVENS Department of Geology, San Jose State University, San Jose, California 95192

Dunne and Gulliver evidently have Rose Formation, Badger Flat Limestone, foothills of the Inyo Mountains. The con- looked fairly carefully at the mapping of Barrel Spring Formation, and Ely Springs tention by Dunne and Gulliver that part of Olson (1970) and Stevens and Olson (1972) Dolomite, crops out on the hill. The strati- this sequence on the hill at location 7 is a with the purpose of attempting to show that graphically highest chert unit, which is as- landslide and part is in place is not sus- the Inyo thrust fault does not exist. They signed questionably to the Ely Springs tained by either the nature of the unit or its agree with most of the previous mapping, Dolomite, becomes increasingly brecciated distribution. Thus, it is clear that all lower but their interpretations differ considerably. as the contact with the Mississippian rock Paleozoic rocks lying west of the wes- I contend that they have failed to invalidate below is approached. This sequence, includ- ternmost, major, northwest-trending fault the thrust-fault hypothesis, that they have ing the chert, is intact, and the brecciated cutting Cambrian rocks (see map in Dunne misinterpreted some of the significant as- chert is completely healed by later chert. and Gulliver's discussion) are part of a sin- pects of the local geology, and that their Dunne and Gulliver grant that some of the gle, coherent block which, between loca- model fails to explain the distribution of lower Paleozoic rock on this hill apparently tions 7 and 10, and elsewhere, can be seen rock units in the area. lies upon Mississippian rock along a fairly to lie above Mississippian rocks (Fig. 1 Dunne and Gulliver have presented a va- flat contact, and the maps presented by here). This observation invalidates the riety of observations, some of which no Olson (1970) and Stevens and Olson (1972) major conclusions of Dunne and Gulliver doubt are valid, but much of the discussion show that the units of this stratigraphic suc- concerning the local geology. deals with very vague interpretations. They cession, including the brecciated chert zone, Dunne and Gulliver's model also is inter- suspect that Stevens and Olson have mis- extend 3.5 km northward along the western nally inconsistent. The Mississippian rocks identified stratigraphic units on two hills (Iocs. 1 and 4 on the map presented in their discussion). This is possible, but they suggest no alternatives. Dunne and Gulliver also state that contacts between lower and upper Paleozoic rocks are different from those shown by Stevens and Olson, but they do not present a geologic map to substan- tiate that view. From their discussion, I would guess that their map would show an impossibly complex geologic picture, with myriad faults abutting one another and always, coincidentally, juxtaposing the same units at the same elevations. Many points in their discussion could be argued, but here I will restrict myself to the one that I consider the most important. The most significant exposures for interpretation of the geology of the area are on the hill between locations 7 and 10. The Figure 1. Inyo thrust fault at location 7. Blocky, dark-colored rock in upper part of hill geology here is quite clear. An orderly stack in foreground is lower Paleozoic; lighter, banded, and smoother slopes just above valley of steeply dipping stratigraphic units, in- floor are underlain by Missisippian rock. A small, high-angle fault in foreground on right cluding the Tamarack Canyon Dolomite, A1 side of photograph offsets thrust fault.

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between locations 2 and 3 and near 5 are ever, that the thrust fault might be ex- Owens Valley region, California — A shown by them as let down by normal plained by large-scale westward gravita- geophysical study: U.S. Geological Survey Professional Paper 438, p. faults against Ordovician rocks. Near loca- tional gliding, similar to that postulated by Ridley, A. P., 1971, Devonian and Mississippian tion 1, westward across about 0.5 km of Stevens and Olson (1972) for emplacement sedimentation and stratigraphy of the alluvial cover from location 2, Dunne and of the Harkless allochthon, but at a lower Mazourka Canyon area, Inyo Mountains, Gulliver's cross section shows no Ordovi- structural level. Detailed mapping in the Inyo County, California [M.S. thesis]: San cian rock, but their text indicates that they Inyo Mountains east of the area under dis- Jose, Calif., San Jose State University, 78 p. Ross, D. C., 1965, Geology of the Independence cussion might shed additional light on this recognized it where Olson and I mapped it. quadrangle, Inyo County, California: U.S. Here, Dunne and Gulliver show the rock at question. Geological Survey Bulletin 1181-0, 64 p. the top of the hill (chert assigned to the Ely Stevens, C. H., 1969, Middle to Late Triassic de- Springs Dolomite) downfaulted onto upper ACKNOWLEDGMENTS formation in the Inyo, White, and northern Paleozoic rock. This downfaulted chert had Argus Mountains, California: Geological Society of America Abstracts with Programs to have been derived from some sort of I thank George Dunne and Rachel Gul- for 1969, pt. 5 (Rocky Mountain Section upper plate, a situation which Dunne and liver for an advance copy of their discus- meeting), p. 78. Gulliver elsewhere (for example, at nearby sion, and William Bilodeau and David An- 1970, Geometry of the Inyo-White Moun- Iocs. 2, 3, and 5) deny. dersen for their criticism of the reply. I re- tains allochthon, eastern California [abs.]: American Association of Petroleum Geol- I conclude, therefore, that the model pro- gret that time restrictions made it impossi- ogists Bulletin, v. 54, p. 872. posed by Dunne and Gulliver, which evi- ble to contact Robert Olson for his reaction Stevens, C. H., and Olson, R. C., 1972, Nature dently was based largely on the brittle style to the discussion and this reply. and significance of the Inyo thrust fault, of deformation of the chert, is not consis- eastern California: Geological Society of America Bulletin, v. 83, p. 3761-3768. tent with the larger features observed in the Stewart, J. H., Ross, D. C., Nelson, C. A., and area, and that the question is not whether COMBINED REFERENCES CITED others, 1966, Last Chance thrust — A there are allochthonous rocks in the area major fault in the eastern part of Inyo but, instead, how much terrain is Dunne, G. C., and Gulliver, R. M., 1976, Super- County, California: U.S. Geological Survey posed synbatholithic deformations in east- allochthonous. Is it only the 3.5-km-long Professional Paper 550-D, p. D23-D34. ern wallrocks, Sierra Nevada batholith, Sylvester, A. G., and Babcock, J. W., 1975, Re- block of Cambrian and Ordovician rock California: Geological Society of America gional significance of multiphase folding in exposed along the foothills of the Inyo Abstracts with Programs, v. 8, p. 846. the White-Inyo Range, eastern California: Mountains, much of the White and north- Nelson, C. A., 1966, Geologic map of the Geological Society of America Abstracts ern Inyo Mountains, or something inter- Waucoba Mountain quadrangle, Inyo with Programs, v. 7, p. 1289. County, California: U.S. Geological Survey mediate? I believe that the existing evidence Geological Quadrangle Map GQ-528, supports the interpretation of the Inyo scale 1:62,500. thrust fault proposed originally by Olson Olson, R. C., 1970, Geology of the northwestern and me: that most of the White and north- Inyo Mountains, Inyo County, California MANUSCRIPT RECEIVED (DISCUSSION) BY THE ern Inyo Mountains are allochthonous and [M.S. thesis]: San Jose, Calif., San Jose SOCIETY OCTOBER 21, 1977 State University, 73 p. MANUSCRIPT RECEIVED (REPLY) DECEMBER 1, that they were emplaced by eastward thrust Pakiser, L. C., Kane, M. F., and Jackson, W. H., 1977 faulting. I recognize the possibility, how- 1964, Structural geology and volcanism of MANUSCRIPTS ACCEPTED JANUARY 20, 1978

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