GUIDEBO.E-lK to the Quaternary Geology of the East-Central Sierra Nevada GUIDEBOOK to the Quaternary Geology of the East-Central Sierra Nevada This guidebook was prepared for the XVI Field Conference of the Rocky Mountnin Section of the Friends of the Pleistocene, October 9-10, 1971. by Michael F. Sheridnn Associate Professor Department of Geology Arizona State University Tempe, Arizona 85281 .. PRICE $5.00 c/o Michael F. Sheridan 2.526 N. 56th Street Phoenix, Arizona 85008 First Edition, October 1971 COVER~blique aerfal view of Bishop, C11li£orni11. U. S. Geologicnl Survey high Copyrip;ht ©by Michael F. Sheridan nltitudc photo, series 744 R, number 208. Approximate scnle of 1:121,000. 2526 North 56th Street, Phoenix, Arizom1 85008 Printed bu Lebeau Printing Company, Phoenix, Arizona CONTENTS Page Introduction .. ....................... .. .. .... .......... .. 5 ACKNOWLEDGEMENTS Glacial Geology . 7 This guidebook is the outgrowth of several guides compiled by Volcanic Geology . ............... 9 R. D. Reger and R. K. Merrill for field trips in Glacial Geology and Volcanology classes in the Department of Geology, Arizona State Road Log .... .. ...... .................... ... .... ....... .. 11 University. These trips conducted by Dr. Troy L. Pewe have led to an integrated picture of the dramatic glacial and volcanic history of this Road Log Day 1 ... .. ....... ....... ............. .. .. ... .. 14 region. I would like to thank Troy L. Pcwc and Jan Sheridan for reading early versions of the manuscript and providing useful comments. Appre­ Road Log Day 2 ........ ..... .. ..... .. ............... .. .... 40 ciation is extended to the Geological Society of America and Robert P. Sharp for permission to use previously published materials. References .................................................. 57 ILLUSTRATIONS INTRODUCTION Page The eastern Sierra Nevada from Bishop to Mono Lake is noted for Figure 1-Index Map ................................... · · · · · .11 the spectacular beauty of its rugged mountains and deep va1leys. This region is a favorite outdoor recreation area in both the summer and Figure 2 - Field stops, Bishop lo Mono Lake .................. .. 12 winter. It is n1so of critical scientific importance for Quaternary geologic Figure 3 - Coyote F1ot warp ................................... 15 studies. The standard Sierra glacial stratigraphy was developed here (Table 1). Figure 4 - Bishop Tuff southern lobe . ... ............ .......... 19 TABLE 1 - Glacial Stratigrnpby• Figure 5-Post-tuff gravels on Shenvin Grade .................. 23 Correlative Sierra Glaciation 3 Neoglacial - Matthcs - 700 years to present.•• Figure 6- Big pumice cut ..................................... 25 Recess Peak3 - 2000 to 2600 years.• 0 3 Hilgnrd - 9000 to 10,500 years?•• Figure 7 - Geologic map of Sherwin Grade area ................. 26 Wisconsimm - Tioga' - about 20.0oo.•• 1 Tennya - about 45,ooo.•• Figure 8 - Bishop Tuff density profile ........ .................. 27 Tahoe' - 60,000 to 75,ooo.•• Illinol:m- Mc;no Ilasin' - about 130,000. • • 4 Figure 9 - Bishop Tuff cooling pattern .......................... 30 Casa Oiablo - nbout 400,000.•• 1 Knnsnn­ Shenvin - older than 710,000 years (Dalrymple, 1965). 1 Figure 10-Joint pattern below fumarolic ridges ..................31 Nebraskan- McGce - ol:lcr thnn 2.6 m.y. (D:ilrymple, 1003). Deadmnn Pass• - between 2.7 m.y. nnd 3.1 m.y. (Curry, 1966). Figure 11 - Location of Long V nJley caldera ... ................ 34 1. Names of Blacl..·wddcr (1931) 2. Names of Shnrp and Ilirmnn (1003) Figure 12 - Stereopair, Convict Lake .. .......................... 37 3. Names of Birman (1964) 4. Names of Curry (1966, 1971) Figure 13 - Flow banding on obsidian dome .... ................. 42 0 This table docs not include some glaciations indicated by Curry (1971, Table 1). Figure 14 - Stereopair, Mono Craters and June Lake ............. .45 ••Absolute age follows Curry (1971, Table 1) Figure 15 - Morainal assembJage, Sawmill Canyon and Bloody Because volcanism, tectonism, and glaciation arc intimately related Canyon .......... ...... · · · · · · · · · · · · · · · · · · · · · · · · · · · 46 process in the Quaternary history of the cast-central Sierra Nevada, radiometric elating of the volcanic rocks has established an unequalled Figure 16 - Stereopair, Sawmill Canyon and BJoody Canyon ....... .47 corroboration of detailed Pleistocene chronology (Table 2). It was here Figure 17 - Spine on Panum Crater ............................ · . 51 that the "ice age" was dutecl at more than 1 million years; then shown to be at least 3 million years (Curry, 1966). Through~ut this period of Figure 18 - Northern Coulee ......... ................... · . · · · · · · 53 active volcanism and glaciation the eastern Sierra escarpment attained as much as 4,000 feet of its pn•scnt majestic relief by warping and nonnal faulting (Christiansen, 1966). This tcctonism has diversified the glacial and volcanic patterns to an extent that has only reccntlv been TABLES imagined. · · Table 1 - Glacial Stratigraphy ............................. · · · · · · 5 The purpose of this text is to present a general view of the geology through an appreciation of the excellent exposures of tvpical units in Table 2 - Dated Volcanic Units ............................ · .. · · 6 the classical sequence. Because many aspects of the Quat~mary geology of this region arc well k"Tiown, heavy reliance is placed on the abundant Table 3 - Chemical Analyses of Bishop Tuff ................... · · · 32 geologic literature. Some classic as well as controversial stops recorded Table 4 - Chemical Analyses of Mono Lake Water .............. · 52 here arc familiar to geologists who have worked this area. Several stops included in the 1965 INQUA VII Field Congress trip I will be familiar. -5- The geology of this area is contained in the 1:250,000 Mariposa Sheet GLACIAL GEOLOGY so1d by the California Division of Mines and Geology. The U. S. The Pleistocene glacial history of this area was initially studied Geological Survey topographic maps covering the route are: Bishop, by I. C. Russell (1885) and later by Eliot Blackwelder (1931), W. C. Mt. Tom, Casa Diablo Mountain, Mt. Morrison, and Mono Craters. Putnam (1949, 1950) and J. H. Birman (IS64). The oldest glacial deposits Geologic maps at the scale of 1:62,500 are available for all of these of this area arc found near Dcadman Pass in the Devils Postpile quad­ quadrangles from the U. S. Geological Survey. rangle. Radiometric ages of volcanic units above and below till of this TABLE 2 - Doted Volcanic Units glaciation indicate that it occurred very close to 3 million years ago Unit Dote Re£ercnce (Curry, 1966, 1971). This location is not easily accessible and will not Christiansen and Gilbert, 1964 Mono Lake sublncustrine 81 years be visited on this bip. eruption Inyo Lo.kes explosion craters 630 ±200 years Rinehart nnd Huber, 1965 The McCce glaciation {Blackwelder, 1931) is represented by deepl~ 1300 years Friedman, 1968 weathered till and boulders found scattered high on mountain summits Pnnum Crater and ridges. The type locality is on the smooth summit of McGee 1440 ±150 years Rubin and Alex11nder, 1960 l\lnmmoth ash Mountain which we will drive past. We will not however, have a chance Northern Coulee 1800 years Friedman, 1968 to examine the McGee till first hand. The great height at which the Southern Coulee 2500 yen.rs Friedman, 1988 McGee till is now found is interpreted by most to be the result of Cnldern north of Punchbowl 5800 years Friedman, 1968 faulting in post-McCee time. Mono nnd Inyo domes 6,400 to 10,200 yclrS Dalrymple, 1967 The next oldest glaciation is the Shenvin (Blacl"'\velder, 1931). Till Mammoth Mounto.in upper 0.15 ±.05 m.y. Curry, 1971 of this advance or series of advances is deeply weathered with constituent coulec boulders of granitic composition easily cut or cmmbled. This till has Mammoth Mountain quartz lntite 0.18 ±.09 m.y. Huber nnd Rinelmrt, 1967 no definitely morainal surface fonn but occurs as a rubble surface near Bnsnlt of Mnmmoth Creek 0.19 ± .04 m.y. Curry, 1971 the west side of Wheeler Crest. The type locality of the Sherwin till (upper unit) ns defined by Blacl"'\velder (1931, p. 895) is at Shenvin Summit. Black­ Bnsnlt of Mnmmoth Creek 0.28 ± .07 m.y. Curry, 1971 welder (1931) erroneously concluded that the Shcnvin till overlies the (middle unit) Bishop Tuff. Doell ond others, 1966 Rhyolite at Whitmore 0.28 ±.03 m.y. Although Shcnvin till crops out in some valleys and high on some Hot Springs hillsides, it is obviously buried by Bishop Tuff in Owens Gorge and in ~fommoth Mountain quartz latite 0.37 ±.04 m.y. Dalrymple, 1964a the roadcut south of Toms Place (Sharp, 1968). The ShC'rn•in till is Curry, 1971 Basalt of Mnmmoth Creek 0.44 z.04 m.y. hence older than the Bishop Tuff dated at 0.71 m.y. (Dalrymple and (lower unit) others, 1965). The Shenvin gfaciation was correlated bv Blackwelder Andesite of Devils Poslpile 0.63 ±.35 m.y. Huber and Rlnchnrt, 1967 (1931) with the Kansas glaciation of the Midwest sequence. Tuff of Reds Meadow 0.66 ±.02 m.y. I Iubcr nnd Rinehart, 1967 (Bishop Tuff?) Although Blackwelder believed that there might have been an Bishop Tuff (11veruge of 6 dates) O.il ±.04 m.y. Dnhymplc and others, 1965 lllinoian glaciation in this area, he did not specify which moraines exemplified this glaciation. It is now generally agreed that the Mono Obsidian of Glass Mountain 0.90 ± .10 m.y. Gilbert nnd others, 1968 Basin glaciation probably correlates with the Illinoian