Frontispiece. Aerial view of the Pine Creek moraine complex CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
THE PLEISTOCENE GLACIAL SEQUENCE OF PINE CREEK, ~ ROUND VALLEY, CALIFORNIA
A thesis submitted in partial satisfaction of the requirements for the degree of Master of Arts in
Geography by Olivia Gentry Robinson ~
June, 1980 p '
The Thesis of Olivia Gentry Robinson is approved:
California State University, Northridge
iii ACKNOWLEDGEMENTS
Phillip Kane stimulated my interest in Pleistocene glaciation, suggested this research topic, and supplied valuable ideas and encouragement. I am appreciative of the comments and guidance given by Robert Sharp in the initial stages of this investigation. I am especially grateful to members of my thesis committee. Robert Howard, chairman, has maintained continued interest and provided numerous suggestions throughout the preparation of this thesis. I am indebted to Bill Bowen for teaching me the necessary skills with which to prepare and construct maps and graphs. I have profited greatly from the fresh ideas, discussion and field assistance provided by Joseph Birman. Field assistance from untold numbers of fellow geomorphology students is fully appreciated. I wish to thank Ray Grey, Geologist for Union Carbide, Pine Creek, California; Curtis Phillips, Phillips Camera House, Bishop, California; Phil Thomas, California Division of Forestry; and John Gaines, California State University Northridge, for the timely information they provided. G. B. Voget kindly allowed unrestricted access to the North Laterals. A financial scholarship was received from the Associated Students, California State University, Northridge to aid in completion of this investigation. I owe special thanks to Murray Milne, who created the space for
iv me to write; and to Peggy Gentry, who has devoted energy and support to this research, both in the field and in the preparation and finalization of the manuscript. And finally, I wish to thank my son Brooks, who is my inspiration.
v TABLE OF CONTENTS
ABSTRACT . . . . . X Chapter I. INTRODUCTION . 1
Purpose. . . I Scope. . . . . 6 The Study Area 6 II. BASIS FOR AGE DISCRIMINATION OF GLACIAL DEPOSITS . 17
Literature Review ...... 18 Procedure...... 22 III. APPLICATION OF AGE-DISCRIMINATION TECHNIQUES TO THE PINE CREEK GLACIAL SEQUENCE. . . 44 Outermost South-east Lateral . 44 Inner South-east Lateral .. 49 South Lateral ... . 52 North Laterals .. . 57 IV. DISCUSSION OF RESULTS. 70 Frequency of Surface Boulders .. 72 Granite Weathering Ratios .... 72 Boulder Morpho 1ogy ...... 76 Interpretation ...... 76 V. CORRELATION OF PINE CREEK WITH OTHER SIERRA NEVADA EAST SLOPE GLACIAL DEPOSITS. 80 Conclusions .. 82 BIBLIOGRAPHY . . . . 89 APPENDIX A: GRAIN-SIZE RELATIONSHIPS DETERMINED BY LABORATORY ANALYSIS ...... 92 APPENDIX B: CUMULATIVE PERCENTAGES OF SILT- AND CLAY-SIZE SEDIMENT DETERMINED BY PIPETTE ANALYSIS, PLOTTED ON ARITHMETIC PAPER ...... 96
vi LIST OF FIGURES
Frontispiece...... i 1. Pine Creek, the Study Area for this Investigation, is Located in the Eastern Sierra Nevada of California. The Pine Creek Moraines Extend into Round Valley which is Bounded by the Sierra Nevada Escarpment on the West and the Volcanic Tableland on the East ..... 2 2. Glacial Deposits of Pine Creek as Mapped by Bateman (1965) ...... 5 3. Geographical Positions of the Pine Creek Moraine Crests ...... 7 4. Wisconsin (?) Glaciation and Climatic Firn Limit in the Sierra Nevada and White Mountains (from Wahrhaftig and Birman, 1965} ...... 10 5. Geology of Pine Creek Area, Round Valley, California (modified from Bateman, 1965, and Strand, 1967) ...... 12 6. Geologic Section across Round Valley Showing Bishop Tuff beneath the Surface (modified from Bateman, 1965, pl. 5) ...... 15 7. Topographic Cross-cutting Relationship in which the Sharp-crested Bouldery Inner South-east Lateral Truncates the Broad- crested Outermost South-east Lateral ...... 19 8. Nested Position of the Inner South-east Lateral within the Outermost South-east Lateral ...... 20 9. Subtle Nesting Relationships of the North Laterals. 21 10. Counts were made within a 30 m (100 ft) by 3 m (10 ft) Plot ...... 23 11. Great Contrast in Boulder Frequencies on Either Side of the North Lateral Crest .. . 25 12. Highly Weathered, Cavernous Boulder ...... 26 13. Extensive Granular Disintegration on Boulder Surface...... • ...... 28 14. Deep Weathering Pan Developed in Granitic Boulder . 30 15. Single Generation of Elephant-hide Texture .. 32 16. Measurements were taken of Mafic Inclusions Protruding above Boulder Surfaces ..... 33 17. Munsell Colors of Till Samples from a Depth of 15 em ( 6 in) and 30 em ( 12 in). . . . 36 18. Distribution of pH Sampling Sites ...•. 38 19. Soil Sample Locations ...... •...... 39 20. Comparison of Wet versus Dry Sieved Samples taken from the Same Location ...... 42
vii 21. Aerial Photograph of the Pine Creek Moraine Camp 1ex...... 45 22. Outermost South-east Lateral Boulder Frequency Count Locations .•...... 48 23. Outermost South-east Lateral Boulder Weathering Ratio Count Locations ...... 50 24. Inner South-east Lateral Boulder Frequency Count Locations ...... 51 25. Inner South-east Lateral Boulder Weathering Ratio Count Locations ...... 53 26. Composite Photograph Showing Displacement of South Lateral Crests as a Result of Faulting 55 27. South Lateral Boulder Frequency Count Locations 56 28. Cobble-strewn Ground Surface of the South Lateral ...... 58 29. South Lateral Boulder Weathering Ratio Count Locations...... 59 30. Broad, Subdued Crest of the Lower North Lateral 61 31. A Contact of Two Glacial Advances on the North Lateral is Delineated by a Sharp, Bouldery Kno 11 . • ...... 62 32. North Laterals Boulder Frequency Count Locations .. . 65 33. North Lateral Ground Surface Covered with Fine Grus and Soil ..•...... 66 34. North Laterals Boulder Weathering Ratio Count Locations ...... 67 35. Highly Weathered Boulder of Low Relief Located on the Lower North Lateral ...... 69 36. Moraine Crest Profiles ...... 71 37. Boulder Frequency Counts on the Outermost South-east Lateral, Inner South-east Lateral, South Lateral, Upper and Lower North Laterals ...... 73 38. Cumulative Frequency of Fresh Boulders Plotted on Arithmetic Probability Paper. Data from the Outermost South-east Lateral, Inner South-east Lateral, South Lateral, Upper and Lower North Laterals ...... 74 39. Supplemental Granite Weathering Counts Combined with Previous Counts for Data Comparison with Figure 38. Data Plotted on Arithmetic Probability Paper...... 74 40. Discordant Moraine Crests of the Inner South-east Lateral and South Lateral...... 78 41. Glacial Deposits of the Study Area as Mapped by Bateman (1965), above, and as Mapped for this Investigation, below ...... 87
viii LIST OF TABLES
1. Comparison of Glacial Sequences, Sierra Nevada, Ca 1 i fo rn i a ...... 3 2. Description of Glacial Deposits, Sierra Nevada, California ...... 4 3. Time-dependent Age Criteria Used in this Study. 46 4. Grain-size Distribution for Soil Samples from the North Lateral Gully and Crest Locations on Either Side, Sieved into Coarse, Medium and Fine Fractions ...... 64 5. Comparison of Boulder Frequency Counts for Several Eastern Sierra Nevada Locations ... 81 6. Comparison of Tioga Age Weathering Ratios with Pine Creek Data ...... 83 7. Comparison of Tenaya Age Weathering Ratios with Pine Creek Data ...... 84 8. Comparison of Tahoe Age Weathering Ratios with Pine Creek Data ...... •.•...... 85 9. Pine Creek Glacial Sequence Age-Assignments .. 86
ix .'
ABSTRACT
THE PLEISTOCENE GLACIAL SEQUENCE OF PINE CREEK, ROUND VALLEY, CALIFORNIA by Olivia Gentry Robinson Master of Arts in Geography
Pine Creek canyon, in the eastern Sierra Nevada, California, is distinguished by large depositional forms, remnants of Pleistocene glaciation. The Pine Creek glacial sequence shows evidence of four distinct glacial stades; identified from oldest to youngest as Mono Basin, Tahoe, Tenaya, and Tioga. Till age assignments are made on the basis of spatial interrelationships, that is, moraine position, extent and continuity; and time-dependent characteristics, for example, weathering, erosion, and deposition. Correlation with glaciations of other Sierra Nevada east slope locations is based on the relative ages of the deposits. Temporal differentiation of the glacial sequence was determined by field investigation using semiquantitative techniques, supplemented by the use of aerial photographs and topographic maps. Granite weathering ratios, boulder morphology and frequency of surface boulders were found to be the most reliable semiquantitative techniques for determining the relative ages of the Pine Creek moraine complex in the time available.
X It is concluded from this investigation that four separate advances are represented in the glacial deposits extending beyond Pine Creek canyon: 1) Tioga, 2) Tenaya, 3) Tahoe, and 4) Mono Basin. The glacial sequence of Pine Creek correlates with the Pleistocene record established for other eastern Sierra Nevada canyons.
xi CHAPTER I
INTRODUCTION
Pleistocene glaciation modified the Sierra Nevada range of California. Impressive glacial deposits are found at the mouths of many canyons along the eastern base of the Sierra Nevada and serve as a reminder that much of the sculpturing of this range was due to glaciation. One of these canyons, Pine Creek (Fig. 1), was chosen as the study area for this investigation. From the mouth of Pine Creek at the base of the Sierra Nevada, conspicuous glacial lateral moraines extend some 4 km (2.5 mi) into Round Valley.
Purpose The purpose of this investigation is to determine the relative ages of the Pine Creek moraine complex and thus enable correlation with other Sierra Nevada canyons. This will enlarge current under standing of the Pleistocene climatic history and glacial record. Tentative glacial sequences for other parts of the Sierra Nevada are included here as Table 1, with descriptions of these glacial deposits listed in Table 2. Bateman (1965, pl. 2) contended that four ages of glacial till are present in the Pine Creek moraines: 1) young Tioga, 2) Tioga, 3} Tahoe, and 4) old Tahoe (Fig. 2). He arrived at this hypothesis using aerial photographs and geologic maps for dividing deposits into
1 2
Figure 1. Pine Creek, the study area for this investigation, is located in the eastern Sierra Nevada of California. The Pine Creek moraines extend into Round Valley which is bounded by the Sierra Nevada escarpment on the west and the Volcanic Tableland on the east. PINE
~:L 0 N ">) % ~
INDEPENDENCE 10 0 10 20 3p .40 Kilometers I II I II I I I I
10 0 110 210 30 40 Miles II II 1111111 I I 3
TABLE 1
COMPARISON OF GLACIAL SEQUENCES, SIERRA NEVADA, CALIFORNIA Suggested Correlation Blackwelder Sharp and Birman Fleisher Birkeland with Continental (1931) ( 1963) • ( 196 7) (1964) Sequence Birman (1964)
Matthes Gilbert Neoglaciation · Recess Peak Basin f,1ountain
Hilgard Wonder Lakes Frog Lake Wisconsin Tioga Tioga Tioga Tioga Glaciation Tenaya Tenaya ... Tahoe Tahoe Tahoe II Tahoe Tahoe I
f~ono Basin Pre-Tahoe Illinoian Donner Lake Hobart
Kansan Sherwin Sherwin
Nebraskan McGee ~1cGee
Sources: Bateman, P. C., and \~ahrhafti'g, Clyde, 1966, Geology of the Sierra Nevada, pt. 1 in Chapt. 4 of Bailey, E. M., ed., Geology of Northern California: California Div. Mines Bull. 190, p·. 165. Fleisher, P. J., 1967, Glacial geology 0f the Big Pine drainage, Sierra Nevada, California (Ph.D. thesis): Washington State Univ., p. 54. 4
TABLE 2
DESCRIPTION OF GLACIAL DEPOSITS, SIERRA NEVADA, CALIFORNIA GLACIATION TYPES OF DEPOSIT AGE CiHTERIA
Tioga lateral moraines about 300 m high End moraines abundant. Dark inclusions, and aplite ir. larger val1eys. End moraines • and pegmatite dikes protrude only slightly from 1.5-5 m high. Thin ground moraines. bedrock or not at all. About 30% of boulders are Scattered erratics on bedrock. weathered. Till surfaces very bouldery. Dissec tion of moraines negligible except by main streams. Tenaya lateral. moraines about 300 m high End moraines largely destroyed. Glacial polish in larger valleys. Rare end still present.on aplite and pegmatite dike surfaces. moraines 8-15 m high. Ground and en dense fine-grained lava. Mafic inclusions moraine and glaciofluvial deposits. and aplite and pegmatite dikes protrude slightly Scattered erratics on bedrock. or not at all. Ahout 50% of boulders are weathered. Till surfaces moc'erately bouldery. Moraines dissected by gullies 3-12m deep. Tahoe lateral moraires 450-600 m high Glacial polish found only on recently uncovered in larger valieys. Ground moraine bedrock. Weathering pits ar.d pans rare and shallow. of gentle relief. Scattered Rock pedestals arc rarely over 2 em high. ~lafic erratics on bedrock. inclusions and aplite and pegmatite dikes protrude as much as 7 em. About 70% of boulders are weathered. Till surface is not markedly bouldery. Moraines dissected by gullies 3-20m deep. Mono Basin Well-formed lateral-moraine Ori gina 1 mm·pho 1ogy better preserved than on Sher11in segments truncated by Tahoe deposits, but only 5% of boulders are unweathered. moraines in Walker Creek and Truncated by Tahoe glacial deposits. More clearly othe~ canyons of the eastern slope related to present drainages than SherWin glacial of the Sierra Nevada. Glaciation deposits. apparently less extensive than Tahoe glaciation.
Source: Wahrhaftig and Birman, 1965, The Quaternary of the Pacific Mountain system in California, in Writ]ht, H. E., Jr., and Frey, D. G., eds •• The Quaternary of the United States: Princeton Univ. Press, p. 303. 5 p '
Figure 2. Glacial deposits of Pine Creek as mapped by Bateman (1965). Qtao =Old Tahoe till, Qta =Tahoe till, Qti =Tioga till, Qtiy =Young Tioga till, Qt =Quaternary talus, Qal =Quaternary alluvium. Study area for this thesis outlined. < 6 age groups on a physiographic basis. A partial concern in this thesis is to determine whether Bateman•s hypothesis for the Pine Creek moraines can be substantiated using semiquantitative field techniques.
Scope This study employed semiquantitative relative dating techniques to interpret the glacial sequence of the moraines extending beyond the mouth of Pine Creek canyon. No evaluation was made of other glacial deposits within the drainage basin. Field investigations were undertaken during several short-term work periods in 1974 and 1975. Sampling sites were noted on the U.S. Geological Survey Mount Tom topographic quadrangle (scale 1:62,500) enlarged to a scale of 1:20,800. In field notes I recorded prominent weathering features and notable variations in surface morphology along moraine crests. Till samples from moraine crests were subjected to mechanical analysis in the laboratory to supplement field data. I used stereoscopic U.S. Forest Service aerial photographs (Project IN-04, flown in 1972) to identify topographic relationships and color differences of the glacial deposits. For the purpose of discussion only, I have divided the Pine Creek glacial sequence into four subdivisions: 1) Outermost South-east Lateral, 2) Inner South-east Lateral, 3) South Lateral, and 4) North Laterals. Figure 3 is a map illustrating the moraine crests, labeled according to their geographical positions.
The Study Area Location and Accessibility 7
Figure 3. Geographical positions of the Pine Creek moraine crests. ······· "f"cof:>.\...S ••••••••••• ················· 1\..\t:..t' •••• \... \.l.. t"' ••••••• c'"\ __,()':··· "{~······· .-:~1>-\... '\~.. .. \... ~>-' ~ •• ... • ••• s:'1\ •••••• • •• "'t"\.l .... ct:,...r 1'\.' •• • ••••• .... .• :\),D.•••• .. ... •• sa ••••• .•.. ···· • / ...··~~~·····~·uTER·M·osT""sourH·:EAs"f"iAr. ..· : : •• ·,~ •••• £R4L .... · . : :· ..·· .. ···· \ : .... <:.::> ·····::...... ····· . . : .·· ~ ,,~~ • • :.·· ~y .. ···· : ~ ~ ... : .· ..· c, ! ./~~s •: ••• .. ;«:- ~ ••• ·•· ••• ('_<(-to?- .. ·· v ...·:.··· ""v _,_N ...... · \. ~ •••••• \.).. v ...sov ''"'"'
I MILES I 8
The Pine Creek drainage basin is on the eastern slope of the Sierra Nevada within the area abounded by latitudes 37°15'N and 37°30'N and longitudes ll8°30'W and ll8°45'W. The moraines of Pine Creek are about 24 km (15 mi) northwest of Bishop, California, occupying a prominent position in Round Valley. The area is accessible from a paved road extending from U.S. Highway 395 to the Union Carbide tungsten mine in Pine Creek canyon, and several unimproved dirt roads. The area is outlined on Figure 2. The area's major geographic features include Round Valley, formed by coalescing fans from the Sierra Nevada escarpment ~nd the Volcanic Tableland, a rhyolite tuff plateau; Mount Tom, a prominent peak bordering the southeastern extent of the Pine Creek drainage divide; and Wheeler Crest, one of the steepest escarpments of the eastern Sierra Nevada, located to the north of Pine Creek canyon.
Geologic and Geomorphic Setting Uplift of the Sierra Nevada Metasedimentary rocks of Paleozoic age and metavolcanic rocks of Mesozoic age have been dislocated and deformed by intrusion of Mesozoic age batholiths. These batholiths consist of diapiric plutons of diverse compositions and textures, the result of magma differentiation and mode of emplacement along zones of structural weakness. Major uplift and westward tilting occurred during Pliocene time. It is inferred that faulting along the east side of the Sierra Nevada took place after westward tilting of the range (Wahrhaftig and Birman, 1965, p. 305). Major faulting within the eastern ma~gin may have been contemporaneous with collapse of the 9
Owens Valley block (Bateman and Wahrhaftig, 1966, p. 167). Estimates of the time and amount of uplift vary, but apparently a major portion of uplift took place during Pleistocene time, raising the Sierra Nevada to its present relief (Axelrod, 1957).
Glaciation of the East Slope of the Sierra Nevada The Sierra Nevada was repeatedly glaciated during the Quaternary. During the late Pleistocene, a complex of glaciers formed a discon tinuous ice cap 434 km {270 mi) long and 32-48 km (20-30 mi) wide along the crest of the Sierra Nevada (Fig. 4) (Bateman and Wahrhaftig, 1966, p. 158). Much of the material eroded by these glaciers was deposited as moraines, which are best preserved in the rainshadow to the east of the Sierra Nevada crest. Correlations of glacial deposits in the Sierra Nevada (Table l) are made difficult because of climatic variations and the resultant range in the amount of weathering and soil development that has occurred in the tills since their deposition. Tectonics and erosion have also acted to conceal much of the glacial history. There is some age control on two of the earliest stades, the McGee and Sherwin tills. Dalrymple (1963, 1964) has radiometrically dated basalts over lain by McGee till as 2.6 million years old and the Bishop tuff over lying Sherwin till as 0.7 million years old. There is, however, some doubt that these two tills represent distinct and separate glacial advances (Birkeland and others, 1971, p. 211). Present knowledge of the east slope Sierra Nevada glacial history is based on studies of individual areas (Birkeland, 1964; Putnam, 1962; Sharp, 1969, 1972; Sharp and Birman, 1963) but detailed correlations acceptable to most 10
Figure 4. Wisconsin (?) glaciation and climatic firn limit in the Sierra Nevada and White Mountains (from Wahrhaftig and Birman, 1965, p. 304). 0 50 NEVADA ------KilometeiS ---WHITE MI. PEAK "~ 1 CALIFORNIA ------· '• Wh, • "'' •• . ooo~
Mountain iucop, including peoks Contours on climatic fir n limit, ~ Isolate d valley and ~ Main drainage d ivide and cliffs above the fitn limit, based on summit altitudes of ~c i rq u e glaciers. L...::::_j of Sierra NevQda • but to o steep for snow accumulation. 0 lowut peaks to have glaciers on their south-facing sides. (Orographic snow limi t is approximately JOO . AOO m. (1000.1500 ft.) lower. Contour interval . 1000 ft . (305 m.JI 1l
investigators have not yet been established.
Bedrock Geology of Pine Creek Basin Lithology. Bedrock of the Pine Creek drainage (Fig. 5, modified from Bateman, 1965, pl. 2) is mainly Mesozoic granite, quartz monzonite and granodiorite. The Pine Creek pendant, an elongate mass of metamorphic rocks, extends about 9 km (5.5 mi) south-southeast from Wheeler Crest to Mount Tom. The pendant consists of micaceous quartz ite, vitreous quartzite, pelitic hornfels, and marble. Diorite, quartz diorite, and hornblende gabbro, intruded into the metamorphic masses as plutons, were later altered and assimilated by granites, leaving small pendants and inclusions (Bateman, 1965, p. 46). Felsic and mafic metavolcanic rocks of Mesozoic age occur in the area surrounding Mount Tom.
Faulting. Bedrock in the Pine Creek drainage is offset by many high angle faults. A series of interconnecting fault segments delineate
the range front fault zone~ Valley-down faults--those down faulted on the valley side--form a nearly continuous line north of Pine Creek. Bateman (1965, pl. 7 and p. 177) suggested the possibility that the fault system branches at the mouth of Pine Creek canyon, joining a south-trending fault extending from Pine Creek to Horton Lake, located southwest of Mount Tom. This valley-down fault is very young because it offsets Quaternary talus cones (Bateman, 1965, p. 178). The Pleistocene moraines extending from Pine Creek canyon have been offset by two valley-down faults. Mountain-down faults, generally due to subsidence and closely resembling warps, are marked by small 12
Figure 5. Geology of Pine Creek area, Round Valley, California.· Modified from Bateman (1965, pl. 2) and Strand (1967). •
Quartz Monzonite Talus Granodiorite Alluvial Fill Granite Alluvial Fan Deposit
Diorite Quartz Diorite Hornblende Gabbro • Glacial Deposits
Felsic Metovolcanics Mafic Metavolcanics • 0 3 mi Co lc - Hornfels Glacier I D I I b 2 4 km Marble - ···...... -- Stream. Lake Pelitic Harnfel Micaceous Quartzite High Angle Fault (inferred----) Vitreous Quartzite Pine Creek Drainage Divide 13
valleys or benches. These faults have been mapped east of Mount Tom (Bateman, 1965, pl. 7).
Relief. Tectonic activity in and around Round Valley is respon sible for many of its landform features. Wheeler Crest, north of Pine Creek is one of the steepest and highest escarpments along the east face of the Sierra Nevada. In the Pine Creek area vertical dis placement has resulted in more than 2438 m {8000 ft) of visibl~ relief. Total displacement would include the depth of alluvial fill between the 1400 m (4600 ft) elevation on the valley floor of Round Valley and the subsurface bedrock. South of Pine Creek, the escarpment diminishes in height as the base gradually comes in contact with the Coyote warp, an extensive structural warp.
Drainage of Pine Creek Present drainage patterns of the Sierra Nevada were already established by the late Pleistocene. These patterns largely controlled the courses of glacial descent {Wahrhaftig and Birman, 1965, p. 305), but in places glaciers were able to override drainage divides. The Pine Creek drainage (Fig. 5) is composed of Morgan, Gable, and Pine Creeks, encompassing an area of approximately 88 sq km (34 sq mi). The drainage basin includes one north-facing glacier at 4600 m (12,000 ft). Drainage patterns are well integrated in the upper reaches of the basin although glacial erosion has produced areas of small scale internal drainage.
Round Valley Geologic Structure of Round Valley. Round Valley is a depressed 14 block, resulting from faulting and warping. Although Round Valley subsided as a virtually coherent block, it underwent internal deforma tion (Bateman, 1965, p. 173). Round Valley is bounded on the west and south by the Sierra Nevada and on the northeast by the Volcanic Tableland, a rhyolite tuff plateau radiometrically dated at 700,000 years (Dalrymple, and others, 1965). An ancient structure, the Coyote warp surface (Bateman, 1965, p. 190) supposedly continues beneath Round Valley and the Volcanic Tableland, dominating the bedrock structure. Gravity data from Pakiser and Kane (1965, pl. 7) suggest that bedrock is buried beneath a relatively shallow accumula tion of alluvium. Bateman (1965, p. 189) stated, 11 The part of the Volcanic Tableland adjacent to the northeast side of Round Valley slopes south-eastward toward the valley as a result of warping, and the downward projection of this surface carries the Bishop tuff beneath the alluvium in Round Valley 11 (Fig. 6).
Sedimentation in Round Valley. Erosion and sedimentation have been effective modifiers of the landscape. Large alluvial fans flank ing Round Valley, alluvial fill of the valley floor, talus, and moraines are constructional features, all products of Quaternary sedimentation processes. It is probable that much of the eminent fan material from Pine Creek originated as outwash from Pleistocene glaciations. Sheridan (1966), analyzing radar imagery of the Bishop area, found that dark image patterns correlate with silt- and clay-sized alluvial deposits and light image patterns correlate with coarser textured fan surfaces. Talus covers extensive areas within the Pine Creek drainage 15
Figure 6. Geologic section across Round Valley showing Bishop tuff beneath the surface. Section line trends approximately east southeast 1.5 km (1 mi) sou~B of he moraine complex. (Modified from Bateman, 1965, pl. 5). A K /Ar 40 date for the Bishop tuff is used as a stratigraphic tool for correlating glacial deposits. sooo'
j::: ::: ::: :::::: d Alluvial Fill
0 _T--L.""J:,-~_t?_...... -_j~ mi 0r 2 3 l . km Hi
{Fig. 5). Especially prominent are large scree slopes along the steep south wall of the canyon. The most conspicuous depositional landform is the morainal complex extending from the mouth of Pine Creek canyon. This complex has an areal extent of approximately 6.5 sq km (2.5 sq mi), exhibiting a maximum local relief of 146m (480 ft).
Climate and Vegetation The Sierra Nevada has a seasonal climate controlled more by topo graphy than latitude, with most of the precipitation in the winter months (Wahrhaftig and Birman, 1965, p. 305). At the higher elevations most of the precipitation falls as snow which may linger through the summer in patches on north-facing slopes. The Pine Creek study area lies in the semiarid rainshadow of the Sierra Nevada. Differences in elevation thus account for the wide ranges of temperature and precipi tation noted in the region. Vegetation is sparse on the moraines, as it is on the floor of Round Valley and the lower mountain slopes. Vegetation within the study area consists mainly of Great Basin sagebrush (Artemisia tridentata), rabbitbrush (Chrysothamnus nauseosus), Mormon tea (Ephedra viridis), annual buckwheat (Eriogonum .?..P£..), cliff-rose (Cowania neo-mexicana) and bush encelia (Encelia frutescens) (_personal communication, J. Gaines, October 1974). CHAPTER II
BASIS FOR AGE DISCRIMINATION OF GLACIAL DEPOSITS
Various techniques have been used throughout the western United States to determine relative ages of alpine glacial deposits. These depositional forms may be differentiated on the basis of: 1) spatial interrelationships, that is, those originating at the time of deposition, and 2) time-dependent characteristics or gradational proc- esses occurring since deposition. To avoid misinterpretation of the glacial history of a canyon, the spatial interrelationships of a glacial sequence must be determined prior to an analysis of unique
time-dependent characteristics for individual advances. The topo~ graphic position, coupled with extent and continuity of a glacial deposit provides a major source of reliable age-discriminating infor mation which may be supplemented with evidence of post-depositional modification. The following principles are implicit in the interpretation of glacial geometric configurations: 1) topographic unconformities are the result of glacial readvance. Previous deposits are obscured or truncated when a glacier of greater magnitude changes course. 2) except where deposits have been overridden by a subsequent, larger advance; the outermost glacial deposit is the oldest, with the younger deposits nested inside. 3) moraine nesting is an indication of successive deposition but not necessarily multiple glaciation. 4) it cannot be inferred from moraine nesting that glacial
17 18
deposits of the same age can be found in similar stratigraphic positions in different canyons. The Pine Creek moraines exhibit both topographic cross-cutting relationships (Fig. 7), caused by directional change in subsequent glaciations, and nesting (Figs. 8 and 9).
Literature Review In his paper on the glacial history of the Sierra Nevada and Basin Ranges Blackwelder (1931) introduced many useful criteria for distinguishing relative ages of till deposits. The criteria include the frequency of surface boulders, boulder weathering ratios and till color. These criteria have been modified and supplemented by other geologists (e.g., Sharp and Birman, 1963; Birkeland, 1964; Fleisher, 1967). Other dating techniques have also been devised and employed but for the most part they have been only locally applicable. This is the case, for example, with Dalrymple's (1964) use of potassium argon dating for interglacial basalts, Axelrod and Ting's (1961) utilization of pollen analysis, and Birkeland's (1968) and Smith's (1968) employment of pluvial lake stratigraphies. According to Morrison (1968, p. 97), 11 no single technique of correlation appears to be completely reliable in all situations. 11 The semiquantitative techniques of Blackwelder have been used by numerous other investigators in many parts of the eastern Sierra Nevada (Putnam, 1962; Sharp and Birman, 1963; Birkeland, 1964; Birman, 1964; Fleisher, 1967; Clark, 1967) but the results of this thesis represent their first application to the moraines of Pine Creek. To 19
Figure 7. Topographic cross-cutting relationships in which the sharp-crested bouldery Inner South-east Lateral truncates the broad crested Outermost South-east Lateral in the foreground
---,-:------,------· ·---~- -· --·
20
Figure 8. Nested position of the Inner South-east Lateral within the Outermost South-east Lateral as viewed from the North Laterals
21
Figure 9. Subtle nesting relationships of the North Laterals as viewed from the Inner South-east Lateral
22 train myself in the application of semiquantitative techniques, I used them in field studies on the Convict Lake moraines studied by Sharp (1969) and my results closely duplicated his.
Procedure I have chosen the methods discussed below which have been used by other investigators on the east slope of the Sierra Nevada. Some techniques yield significant results butothersprove inappropriate for the Pine Creek moraines.
Frequency of Surface Boulders The criterion of boulder frequency counts was originally suggested by Blackwelder to be a characteristic that varied with moraine age.
11 In general, the younger moraines are more bouldery than the older ones 11 (Blackwelder, 1931, p. 878). The concept of boulder frequency counts, developed by Blackwelder and expanded by Sharp, is based on two assumptions. First, initial boulder frequencies are equal for all moraines, and second, the number and size of surface boulders is reduced by weathering. Slight variations of procedure are employed by different investigators although all rely on the objectivity of boulder frequency counts. I counted all boulders greater than 0.30 m (1.0 ft) in diameter exposed on the surface along a moraine crest within a plot 30 m (100 ft) long by3 m (10ft) wide (Fig. 10). By restricting the sampling sites to moraine crests, local weathering variables, such as aspect, were eliminated. Care was taken in locating the plots on the crests because large discrepancies of boulder frequency often occur on either 23
Figure 10. Counts were made within a 30 m (100 ft) by 3m (10 ft) plot
24
side of a morainal crest (Fig. 11).
Granite Weathering Ratios Blackwelder (1931, p. 877) recognized various degrees of grano diorite weathering: 11 a) almost weathered, b) notably decayed on the surface but still solid, c) greatly weathered, cavernous or rotten. 11
11 11 Blackwelder•s ratio was modified by Birman to fresh versus weathered • Birman (1964, p. 25) determined the following ratio of mean values from several eastern and western slope Sierra Nevada drainages: Tioga 70:30 Tenaya 51:49 Tahoe 33:67 In his opinion these values should be valid in other Sierra Nevada moraine complexes.
In this investigation a determination of the ratio of 11 fresh 11 granitic boulders to 11 Weathered 11 granitic boulders was made along moraine crests by counting boulders 0.30 m (1.0 ft) or more in diameter within a 30 m (100 ft) by 3 m (10 ft) plot. A weathered boulder was considered to be one in which more than half of the surface exhibits weathering to a depth greater than the average grain diameter. Other wise it was classified as fresh. Weathered boulders are partially de composed (Fig. 12), often crumbling or producing a hollow-like sound when hit with a hammer. Care was taken to eliminate personal bias through the use of a field assistant to record the counts.
Non-granitic Ratios Sharp (1969, p. 69; 1972, p. 2238) discussed an age criterion based on the ratio of granitic to non-granitic boulders on a moraine 25
Figure 11. Great contrast in boulder frequencies on either side of the North Lateral crest
26
Figure 12. Highly weathered, cavernous boulder
27
crest. In some areas it is a powerful indicator of age, the non granitics being more resistant to weathering. I recorded the number of non-granitics per plot at the same time and locale as the granite weathering ratios. It was decided that non-granitic ratios are not suited for the tills of Pine Creek. The internal range of percentages along a moraine crest is highly variable, making a comparison between deposits insignificant.
Boulder Morphology Several morphological characteristics have been used by other investigators as supplemental evidence for till age-discrimination. In this investigation the degree of development or preservation of the following characteristics were noted along each moraine crest: 1) glacial striations or polish, 2) granular disintegration or boulder scaling (exfoliation), 3) boulder shape and relief, 4) weathering pits or pans, 5) elephant-hide texture, and 6) relief of mafic inclusions on boulder surfaces.
Glacial Striations or Polish The degree of preservation of glacial striations or polish on the original surface should be indicative of the duration of exposure and amount of weathering that has taken place. Glacial striations or polish are uncommon features on the Pine Creek moraines.
Granular Disintegration and Boulder Scaling (Exfoliation) The extent to which granular disintegration (Fig. 13) or boulder scaling (exfoliation) is exhibited by boulders on a particular moraine crest is indicative of the relative age of the deposit. The degree to 28
Figure 13. Extensive granular disintegration on boulder surface
29 which boulder size is reduced as a result of granular disintegration and scaling can be determined only when part of the boulder's original sur face is present for comparison. Scaling rinds were often observed adjacent to the parent rock, which had a fresh appearance where the outer surface had been shed.
Boulder Shape and Relief Boulder shape and relief were used as supplemental evidence for the relative age of a deposit. Characteristic boulder shape was noted for each moraine crest. Shapes varied from extremely angular to well rounded. Boulder relief is the maximum height a boulder stands above ground-level, and is a qualitative tool used in recognizing tills of separate advances. In general, boulders located on older deposits display lower relief than those located on younger till. Boulder relief is the result of weathering; a combination of boulder size re duction and the build up of grus around the base of the boulder.
Weathering Pits and Pans Pits and pans are weathering features most commonly developed on boulders of older tills. Some pitting and pan development occurs along fracture joints or zones of weakness, while others are randomly located. Often coalescing pans form large, irregularly-shaped basins. Pans may have soil, grus, or disintegrated material filling the lower cavity if aeolian activity is not intense enough to remove it (Fig. 14).
Elephant-hide Texture Elephant-hide texture is characterized by irregularly-shaped 30 " '
Figure 14. Deep weathering pan developed in granitic boulder
31 polygon fractures on the surface of some weathered granitic boulders. Where portions of the elephant-hide texture has been removed by scaling, the inner, exposed area is devoid of the texture (Fig. 15). This phenomenon is supported by other investigators who report the development of a single 11 generation 11 of elephant-hide or tortoise shell texture {Fleisher, 1967, p. 47; Kane, 1975, p. 60). The absence of this feature is assumed to be the result of: 1) insufficient weathering, or 2) advanced weathering to the point of removal, through scaling.
Relief of Mafic Inclusions on Boulder Surfaces The granite/mafic ratio is relatively insensitive to outside factors other than lithologic variation. Mafic inclusions are less susceptible to weathering than coarse-grained granite. Therefore, note was made of the relative abundance of mafic inclusions within granitic boulders and measurements were taken of inclusions observed protruding above boulder surfaces (Fig. 16).
Soil Characteristics Soil properties that develop as a function of time have been used extensively as till age-discrimination criteria (Sharp, 1969, 1972; Nelson, 1954; Birkeland, 1964). The soil characteristics sampled for this investigation are: 1) soil color, 2) pH, and 3) grain-size relationships within the till.
Color Degree of soil development being a function of age, other things equal, soils developed on older tills should display lower color hues 32
Figure 15. Single generation of elephant-hide texture
33
Figure 16. Measurements were taken of mafic inclusions protruding above boulder surfaces
34
(Birkeland, 1964, p. 812) than soils on younger tills. It should be noted at this juncture that rates of soil formation are inhibited and slowed considerably in the semiarid environment of the east side of the Sierra Nevada. Birkeland and Janda (1971, p. 2497, p. 2504) concluded that degree of soil development is a useful tool in correlating glacial deposits only as far south as Virginia Creek, about 105 km (65 mi) north of Pine Creek. Soils south of Virginia Creek exhibit signs of weathering however it is unknown why a strong textural B horizon has not developed. They found undefined textural B horizons in soils developed on Mono Basin and younger deposits, with only slight variations in color. Fleisher (1967, p. 49) was able to differentiate tills of different age through color variation from a distance of 0.8 km (0.5 mi) or more in the Big Pine drainage area, south of Pine Creek. Although Fleisher was able to make such long range comparisons of till color, I was unable to use color in differentiating the tills of Pine Creek from a distance even with the aid of color aerial photographs. Ap parent variations in till color seen on the aerial photographs may be due to microclimatic conditions, such as vegetation, slope, elevation, and burned surface areas rather than resulting entirely from weathering. Sharp (1969, p. 70) noted the color characteristics of till samples taken at 15 em (6 in) intervals to a depth of 0.6 m (2 ft) to 0.9 m (3 ft) from the moraines at Convict Lake. After dry sieving, the fines (less than 0.8 mm) were tested for color. He found the method most effective in differentiating older deposits which had developed greater weathering profiles and a regular progression of color. 35 f '
Inconsistencies in color were found on immature deposits. In part, the highly variable conditions were attributed to lithologic and environ mental influences. In this investigation dry soil color was determined by means of a Munsell soil color chart from the fine (less than +4.0 phi (0.06 mm)) fraction after dry sieving in the laboratory. Samples were taken from holes dug on moraine crests at 15 em (6 in) and 30 em (12 in) depths. Only minor soil color differences were noted with depth (Fig. 17). Till colors are of two hues, either 10 YR or 2.5 Y. Often more exten sive color variations occur within a single deposit than when a color comparison is made between deposits. pH Increasing soil acidity, expressed as decreasing soil pH is a characteristic developed as a function of time. pH measurements have been used by investigators as a tool to distinguish the relative age of glacial deposits. Birkeland and Janda (1971, p. 2499) in their soil study of the eastern Sierra Nevada found that pH profiles stay fairly constant. Sharp (1972, p. 2239-2243) tested till pH values at Virginia Creek and Green Creek, noting greater leaching in the older deposits, which produced a distinct decrease in pH within a well-defined weathered zone. Nelson (1954, p. 337) discovered inconsistent pH test profiles in studies of the glacial deposits of the Frying Pan River drainage, Colorado. In this investigation pH measurements were determined with a LaMotte Morgan Soil Test Outfit. Samples were taken from test pits at depths of 15 em (6 in) and 30 em (12 in). Comparisons of pH values were 36 I' '
Figure 17. Munsell colors of till samples from a depth of 15 em (6 in) and 30 em (12 in). Colors range from Grayish Yellow Brown (10 YR 5/2) to Dull Yellow (2.5 Y 6/3) ------· ------
15 15 CM (6 IN)
(,f) w .....J a... ~ <( 10 (f) lL 0 0:::: w co 5 ~ :::) z
0 5/3 6/2 10 YR 2.5Y
15 . 30 CM (12 IN) - (f) w .....J ~ 10 <( (f) . lL . - 0 0::::w 5 co . .- ~ . ::::) z 0 C1 513 6/3 &'2 6/3 - 10 YR 2.5Y. ... 37 made on: 1) unsieved samples, and 2) the fine (less than +4.0 phi (0.06 mm)) fraction of dry sieved samples. The range of pH values is small, with all samples falling between 6.8 and 6.4. No trend in pH values could be determined either by comparing separate glacial advances (Fig. 18) or through depth profiles, thus they were eliminated as a tool for age-discrimination at Pine Creek.
Grain-size Relationships within the Till Grain-size relationships within the till are presumed to be an indication of the amount of weathering that has occurred since deposi tion. By using mechanical analysis in the laboratory, a determination can be made of the percentage of coarse, medium and fine grained material in a deposit. The assumption is that older deposits contain a greater percentage of fines due to longer weathering periods. Results of mechanical analysis of till samples from the Frying Pan drainage indicate a general trend for younger deposits to contain coarser fragments than older deposits (Nelson, 1954, p. 338). However, it was concluded that the differences were too small to be significant. Sharp (1969) employed the technique of grain-size distribution analysis on the Convict Lake moraines and later, on the moraines at Bridgeport Basin (Sharp, 1972). He attributed consistent grain-size distribution characteristics to till age differences, the debris becoming finer with weathering. Grain-size relationships were determined for the Pine Creek moraines through the following sampling and analysis procedures: 1) sampling: using a spot-sampling method, samples were selected from a representative, moraine crest location (Fig. 19). Care was taken to avoid digging in areas •• •••• ••• • •• •• •• •• •• • •• •• • •• • • ••• ..• '"• •• •• • • •• •• • •• • •• • •• • •••• • • • •• ••••••• • •• •• •• •• •• ••• ...... •• •• •• •• •• •••• •• • ••• •• •• •• •• •• ••• ••••••• 38 •• •••••• •••• •• ••• •• •••• •• •• ••••• •• •• •• ••• ••• •• • ••• •• •• ••• •• •• •• •• •• •• •• ••• •• • •• •• •••• •• •• • ••• •• • 71 \ .77 •• •• •• •• •• •• •• • •• •• • •• • •• • • • •• 79 •• PLOT DEPTH • • •• • • 78 • • •• 78 ( 6 in) • •• • 15 em 6.6 • •• • 78 30 em (12 in) 6.6 •• •• 79 15 em ( 6 in) 6.6 •• 79 30 em (12 in) 6.6 e66 38 30 em (12 in) 6.8 •• 66 30 em (12 in) 6.6 • 71 15 em ( 6 in) 6.6 71 30 em (12 in) 6.4 77 15 em ( 6 in) 6.6 77 30 em (12 in) 6.4 39
Figure 19. Soil sample locations •• •••• •••• •••• •". • • • • •• ~· • •• : • ·..• \--•• •• • • •••• • •• •• ••• • •• •• •• ••••• • •• •• •• •• ••••••••• •• •• •• •• •• •• •• •• •• ...... •• •• ••• •••• •• •• •. ••...... •• ••• •• ••• ••• • •••• .... • ••• • • •• •• •• •• •• •• •• •• • ••• •• •• •• •• ••• • •••• • • ••• •• •• • ••• • •• • .\. '• • • •• • ~'• •• + .. •• t\ •- •• ~~ 40
affected by nearby boulders, vegetation or animal life (e.g. ant hills). Samples were taken from depths of 15 em (6 in) and 30 em (12 in), placed in soils bags and labeled. Large pebbles and vegetal matter were omitted from the sample selection. 2) analysis: a) in the laboratory the sample was placed in a mortar. The aggregates were broken up with a pestle using an up and down motion. b) the sample was sieved by hand and everything greater than -2 phi (4.00 mm) discarded. c) 100.0 grams were measured out of the remaining sample. d) the 100.0 gram sample was sieved in 6 phi fractions: -1 (2.00 mm), +0.75 (0.59 mm), +2 {0.25 mm), +3 {0.13 mm), +4 (0.06 mm) and finer than +4 {0.06 mm). Screen sizes were selected on the basis of availability from the very coarse, coarse, medium, fine and very fine sand classifications. e) the sample was sieved for 15 minutes using a Ro-Tap shaker. f) each size fraction was weighed and recorded. A comparative analysis of 15 em {6 in) and 30 em {12 in) samples located along a moraine crest yielded no definitive weathering trend. Labora- tory analysis results are listed by sampling location in Appendix A. As a result, various alternative procedures from thosedescribed above were attempted but no characteristic weathering pattern became apparent: 1) a few samples were divided, using a sample splitter. One half was oven-dried prior to sieving and the other half was allowed to dry naturally. The experiment produced no significant differences in the sieved fraction. 2) the six sieved fractions were grouped into various coarse, medium and fine sand categories. The larger class intervals did not result in a uniform sampling classification, there being too great a variation of percentages in a fraction-size within the same deposit. 3) comparisons were made of individual sampling sites. Weathering patterns were often reversed from those anticipated by spatial interrelationships of the glacial sequence. 4) the mean was calculated for samples taken from deposits of individual advances. Differences between means 41
of separate advances were highly variable. Quaternary researchers have often used the presence of a well defined, clay-rich zone (B horizon) as indicative of a relatively mature soil. Birkeland (1964, p. 818) found a sharp distinction could be made in the northern Sierra Nevada between soils developed on Tahoe till and soils on older tills by the presence or absence of a B horizon. Birkeland and Janda (1971, p. 2495, 2510) attempted to use soil clay mineral assemblages to differentiate deposits of different age in the eastern Sierra Nevada. They concluded that factors other than time or paleo-climatic variation are responsible for clay formation. No textural B horizon has been distinguished on the Pine Creek moraines by this investigation. However, three samples were divided- one half was dry-sieved and the other half was wet-sieved in an attempt to break down cohesive aggregates formed by the fine silt- and clay-sized particles. The tendency for coarse particles to de crease with the simultaneous increase in fines is illustrated in Figure 20. Pipette analysis, which measures the settling velocity of the particles, was conducted on four additional samples, after wet-sieving, to differentiate the silt- and clay-sizes. A summary of the analysis is contained in Appendix B. The results suggest only minor variations in the cumulative percentages of silt and clay computed for samples taken from 15 em (6 in) and 30 em (12 in) depths. Clay content (less than +8 phi (.004 mm)) in the samples is minimal. In summary, soil characteristics have long been a diagnostic tool for till age-discrimination by investigators in Quaternary research. The time-dependent qualities of soils make their general applicability 42
Figure 20. Comparison of wet versus dry sieved samples taken from the same location PLOT 54 I I I I NORTH LATERAL (!) (!)
lJ.J lJ.J 3: 3:
PAN t. 3 2 0. 75 -1 PHI PAN t. 3 2 0.75 -1 PHI
DRY
PLOT 50 1- 36% I ~ 40~( ...... ___ _ I NORTH LATERAL (!) lJ.J ' lJ.J 3: 20 3:
PAN t. 3 2 o. 75 -1 PHI PAN t. 3 2 0 • 75 -1 PHI
DRY WET
46% PLOT 26 I I I INNER SOUTH- EAST I (!) (!) LATERAL lJ.J lJ.J 3: 3:
PAN t. 3 2 0. 75 -1 PHI PAN t. 3 2 0 • 7 5 - 1 PHI 43 useful in stratigraphic subdivision. The degree of soil development, indicated by color, pH, and grain-size relationships, at Pine Creek was found inapplicable in differentiating till ages, although these same techniques were found valid in other areas. However, it was noted that the ease of digging a test pit can be indicative of the relative age of the deposit; a greater proportion of cobbles and boulders being found in young moraines. CHAPTER Ill
APPLICATION OF AGE-DISCRIMINATION TECHNIQUES TO THE PINE CREEK GLACIAL SEQUENCE
From an aerial perspective, the Pine Creek glacial sequence displays a marked contrast in moraine morphology (Fig. 21). Four morphologically distinct subdivisions of the Pine Creek moraines: 1) Outermost South-east Lateral, 2) Inner South-east Lateral, 3) South Lateral, and 4) North Laterals, will be discussed utilizing the age criteria identified in Table 3 as a basis for age-discrimination. Any one criterion used alone is singularly unreliable for age-determination (Birman, 1964, p. 13), but a combination of methods provides a means for the comparison of glacial deposits.
Outermost South-east Lateral Located outermost on the south side of the moraine complex, this moraine reaches the lowest elevation of all the glacial deposits. The western, up-valley extent has been truncated by a subsequent glacial advance. The distinguishing characteristic of this deposit is its discontinuous spatial relationship with the total glacial sequence. This topographic unconformity is indicative of a glacial readvance. The Outermost South-east Lateral trends in a general east-west direction for a distance of approximately 1.6 km (1 mi). Maximum relief, measured from Pine Creek to the moraine crest, is 30m (100ft).
44 45
Figure 21. Aerial photograph of the Pine Creek moraine complex. Note recessionals stemming from the sharp-crested South Lateral. 46
TABLE 3
TIME-DEPENDENT AGE CRITERIA USED IN THIS STUDY
.•
CRITERIA COMMENTS
Frequency of Surface Boulders Generally a Good Supplemental Indicator of Age
Granite Weathering Ratios Most Consistently Dependable of ~11 Weathering Criteria
Non-granitic Ratios Technique Inappropriate at Pine Creek
Boulder Morphology Locally Applicable and Gene_rally Reliable
Glacial Striations or Polish Granular Disintegration and Exfoliation Boulder· Shape and Relief Weathering Pans Elephant-hide Texture Relief of Mafic Inclusions on Boulder Surfaces
Soil Characteristics Technique Inappropriate at Pine Creek
Color pH Grain-size Relationships within the Till This relief diminishes to approximately 15m (50ft) at the toe of the deposit, where all traces of a terminal arc are missing. An unimproved dirt road traverses the toe, from the town of Rovana to a dump site, closed in 1973. A firebreak, maintained by the State of California Division of Forestry, has been in existence since 1955 (personal commu nication, Phil Thomas, March 24, 1975). The break, which is cleared by hand, provides a means of fire control for the area and is a prominent feature crossing the Outermost South-east Lateral, Inner South-east Lateral and the North Laterals. The North Laterals are intersected by a second firebreak to the east of this location. The moraine is well-formed, broad-crested, and dissected in numerous places by deep rills and gullies. Weathering characteristics noted include: 1) frequency of surface boulders, 2) granite weathering ratios, 3) granular disintegration and boulder scaling, 4) boulder shape and relief, 5) weathering pits and pans, 6) elephant-hide texture, and 7) relief of mafic inclusions on boulder surfaces.
Frequency of Surface Boulders The median boulder frequency is 64 per 30 m (100 ft) by 3 m (10 ft) plot with a range from 45 to 87. Figure 22 shows 20 locations at which surface boulder frequencies were determined. Local ground sur faces are covered with cobbles under 0.30 m (l ft) in diameter, grus, and soil.
Granite Weathering Ratios Fresh boulders were counted within 18 plots. The range of fresh boulders varied from 11 to 34 percent; with a median value at 28 48
Figure 22. Outermost South-east Lateral boulder frequency count locations RANGE 45-87 MEDIAN 64 COUNTS 20
BOULDER FREQUENCY 49
percent fresh boulders per plot (Fig. 23).
Boulder Morphology Boulder granular disintegration varies locally. Boulders are rounded and often split or shattered. Angularities occur when part
of the original, rounded surface is adjacent to the 11 fresh" split. Large pans have developed on different surface exposures or orienta tions in highly weathered boulders. One pan measured 24 em (9.5 in) deep and 10 em (4 in) by 23 em (9 in) across. Many boulders show some evidence of elephant-hide texture on the surface. Some contain mafic
inclusions which protrude as much as 6 em (2.5 in).
Inner South-east Lateral Nested within the Outermost South-east Lateral, this moraine is not as far-reaching in its down-valley extent. The topographic cross cutting relationship exhibited by this deposit indicates that the glacier took a more northerly course than the glacier which deposited the Outermost South-east Lateral. The distance is 1.8 km (1.1 mi) from the toe to the arbitrary boundary of this deposit, where the crest joins the recessional crests of the South Lateral. Maximum relief from Pine Creek to the crest is 122 m ( 400 ft) . Weathering characteristics contrast sharply with those noted for the Outermost South-east Lateral. Not only is the morainal crest higher, it is sharper and considerably more bouldery.
Frequency of Surface Boulders Boulder frequency counts are inconsistent (Fig. 24), ranging from 50
Figure 23. Outermost South-east Lateral boulder weathering ratio count locations. Percentage of fresh boulders is indicated. RANGE 11-34 MEDIAN 28 COUNTS 18
PERCENT FRESH 51'
Figure 24. Inner South-east Lateral boulder frequency count locations I 173. 217. 85. RANGE 59-187 59. 161 • MEDIAN 161 118· COUNTS 13 101 • 115.
BOULDER FREQUENCY 52
59 to 187. The median for 13 counts is 161. A great morphological variation occurs on the moraine; from broad areas of low-relief to places where the crest is barely wide enough to locate one 30 m (100 ft) by 3 m (10 ft) plot. Ground surfaces are covered with very coarse grus and small cobbles, often to the extent that it was difficult to locate a soil test site.
Granite Weathering Ratios Granite weathering ratios are fairly homogeneous, ranging from 34 to 65 percent fresh (Fig. 25). The median determined for 13 counts, is 59 percent fresh boulders per plot.
Boulder Morphology Granular disintegration is not extensive, in fact, very few highly weathered boulders were noted. Boulders are characteristically angular to moderately rounded, with few developed weathering pans. Elephant hide texture is absent. Mafic inclusions are minimal, projecting 3 em (1 in) or less.
South Lateral This deposit, extending from the base of the Sierra Nevada, con sists of one prominent, knife-sharp ridge which fans into a series of recessional moraines. The South Lateral extends a distance of 2.6 km (1.6 mi) and reaches a maximum relief, from Pine Creek to the crest, of 146m (480 ft). The recessionals fanning off the South Lateral are very complex, poorly defined on the ground, evident on a topographic map, and distinct in aerial photographs (Fig. 21). A small, well preserved, sharp-crested lateral moraine hugs the inner slope of the 53
Figure 25. Inner South-east Lateral boulder weathering ratio count locations. Percentage of fresh boulders is indicated RANGE 34-65 64• 63. MEDIAN 59 59. COUNTS 13 38. 34•
PERCENT FRESH 54 more extensive south lateral. Both the South Lateral and small, inner lateral crests have been offset by valley-down faults (Fig. 26). Dis placement is especially evident on the small, inner lateral. A noteworthy characteristic of the South Lateral is the subtle succession of irregularly-spaced outliers or spurs, visible on the upper one-third of the south slope. An imaginary line can be traced from the crests of each of the outliers, which stretch the length of the massive South Lateral. This observation from aerial photographs, coupled with field examination, is significant in that it suggests a remnant of an earlier glacial advance. Similar evidence was found at Convict Lake and has been interpreted by Sharp (1969, p. 83-85) to be the product of more than one glaciation. A flat bench, heavily dissected, extends along the outer slope of the 300 m (1000 ft) Convict lateral. The bench, located at a level linking the upper one-third of the slope, is apparent on most spurs between gullies. Interpretation of the weathering criteria for the South Lateral is complicated by the complex nature of the spatial relationships of this deposit. It was often difficult to determine the exact location of the recessional crests. Plots were positioned to obtain an unbiased cross section in areas where rock outcrops were surrounded by large expanses of soil and grus.
Frequency of Surface Boulders The calculated median of 224 boulders per plot is unreliable as an indicator of boulder frequency. Counts are extremely inconsistent, ranging from 93 to 391 (Fig. 27). Recessional moraine ground surfaces are locally littered with 55
Figure 26. Comoosite photograph showing displacement of South Lateral crests as a result of faulting
56
Figure 27. South Lateral boulder frequency count locations /
.226 .205 ·234 •228 91 •
·226 f
RANGE 93-391 MEDIAN 224 COUNlS 17
BOULDER FREQUENCY 57 pebbles and cobbles less than 0.30 m (1 ft) in diameter, coarse grus and soil. The largest boulder frequency count (391) was obtained from a plot located at the junction of a recessional and the South Lateral crest. No ground surface was visible within the plot, thus traversing was difficult and necessitated hopping from boulder to boulder. The well-defined South Lateral crest throughout much of its extent is barely wide enough for one 30 m (100 ft) by 3 m (10 ft) plot. The ground surface, where visible, is covered with cobbles (Fig. 28). The task of excavating a soil test pit met with some resistance from sub surface deposits!
Granite Weathering Ratios Granite weathering ratios determined at 17 localities range from 48 to 97 percent fresh boulders, with a median of 91 (Fig. 29). The data are congruent when one count of 48 percent fresh is omitted. The unrelated count was taken in a locale of questionable representation.
Boulder Morphology Granular disintegration is apparent only on large boulders; most appear unweathered. Numerous boulders are shattered or split into two or more sections. Boulders are typically angular, of high-relief and large size. No examples of weathering pans or elephant-hide texture were seen. Protruding mafic inclusions were noted on one recessional moraine. In all other cases they were surficial features, where weathering had not progressed enough to expose the mafic xenoliths.
North Laterals The northern counterparts of the lateral moraines described in the 58
Figure 28. Cobble-strewn ground surface of the South Lateral I 59
Figure 29. South Lateral boulder weathering ratio count locations. Percentage of fresh boulders is indicated. I
•as .92 • 89 91 86 • • •87
•97 .91
·86
RANGE 48-97 MEDIAN 91 COUNTS 17
PERCENT FRESH 60
preceding sections are unique and problematical. During the initial reconnaissance it became evident that interpretation of the Pine Creek glacial sequence hinged on further investigation of these deposits.
Sharp (1969, p. 68) stated: 11 Comparisons between lateral moraines on opposite sides of a valley ... are often not satisfactory... Weathering characteristics exhibited by the lower, down-valley portion of the till are in distinct contrast with those for either of the opposing lateral crests (the Outermost South-east Lateral or Inner South-east Lateral). The lower morainal extent is a broad, subdued, splayed-out form (Fig. 30). Weathering features are distinguished from any others in the Pine Creek glacial sequence by the amount of disintegration that has occurred. Contrasting sharply with these weathering criteria are those noted for a subsequent glacial advance delimited by the hummocky moraine crest illustrated in Figure 31. The North Lateral contact is delineated by a knoll which ascends steeply from the broad, highly weathered crest up-valley from the second firebreak. The knoll is sharp, bouldery and trimmed-up by erosional and fluvial activity. The crest descends abruptly beyond the knoll, narrowing to approximately 1 m (3.3 ft) in width. The boulder-strewn crest, at the point of max imum restriction, heads a large gully filled with fine-grained sediment. Soil samples taken in the gully were compared under a microscope with samples from an adjacent crest plot. Clean, angular and fairly well sorted grains were found in the 15 em (6 in) gully sample. The 30 em (12 in) sample contained s.imilar angular material, howeyer there was some aggregation of fines onto the large matrix constituents. Both 15 em 61
Figure 30. Broad, subdued crest of the lower North Lateral f 62
Figure 31. A contact of two glacial advances on the North Lateral is delineated by a sharp, bouldery knoll I 63
(6 in) and 30 em (12 in) samples from the adjoining site contained very poorly sorted, extremely angular particles which were stuck to gether like bread crumbs. Two samples obtained from the gully were sieved in the laboratory and divided into coarse, medium and fine fractions. The results are compared in Table 4 with samples treated in a similar manner from crest sites on opposing sides of the gully. The three sites represented display a noticeable difference in grain-size proportions. Although grain-size relationships have not been utilized as a diagnostic tool for age-discrimination on other Pine Creek till deposits, in this instance they must be regarded as a valuable method for quantitatively verifying a conspicuous morphological difference. Data contained in Figures 32 and 34 identify clearly the contact between the two deposits.
Frequency of Surface Boulders Counts taken from 25 plots located on the lower North Lateral have a median value of 37 and range from 14 to 67 (Fig. 32). Boulder fre quencies are less here than on any other deposit mapped. The ground surface is covered with fine grus and soil (Fig. 33). Large areas are completely devoid of boulders and cobbles. Few, if any, pebbles were encountered while digging soil test pits. The area just east of the second firebreak is highly vegetated and more bouldery in appearance. Four plots located on the upper North Lateral beyond the contact have a median of 157 boulders per plot, determined from a boulder frequency range of 124 to 189.
Granite Weathering Ratios 64
TABLE 4
GRAIN-SIZE DISTRIBUTION FOR SOIL SAMPLES FROM THE NORTH LATERAL GULLY AND CREST LOCATIONS ON EITHER SIDE, SIEVED INTO COARSE, MEDIUM AND FINE FRACTIONS LOCATION FINE ~1EDIUM COARSE (+30, +40 .• pan) (+20) (-10. +0.750)
Lower North Later·al Fl ot 77 15 em ( 6 in) 49.10 27.50 23.20 30 em (12 in) 45.65 27.15 26.85
Gully Plot 71 15 em ( 6 ; n) 63.95 32.80 3.25 30 em (12 in) 59.75 32.40 7.70 Col 15 em ( 5 in) 65.50 30.50 3.80 30 em (12 in) 58.50 32.70 8. 75
Upper North Lateral Plot 72 15em(6in) 38.25 21.50 39.95 30 em ( 12 in) 36.50 23.30 40.05
'· 65
Figure 32. North Laterals boulder frequency count locations RANGE 14-67 124-189 MEDIAN 37 157 COUNTS 25 4
BOULDER FREQUENCY
/ 6 66
Figure 33. North Lateral ground surface covered with fine grus and soil I 67
Figure 34. North Laterals boulder weathering ratio count locations. Percentage of fresh boulders is indicated. RANGE 0-21 82-92 MEDIAN 8 86 COUNTS 25 4
PERCENT FRESH
I 68
On the lower moraines the range in granite weathering ratios is between 0 and 21 percent fresh for 25 plots, with a calculated median of 8 percent fresh boulders (Fig. 34). The low median value obtained by the counts is indicative of the highly weathered nature of this deposit. By comparison, counts taken beyond the contact have a median of 86 percent fresh boulders per plot, based on four counts ranging from 82 to 92 percent.
Boulder Morphology A marked difference in granular disintegration occurs at the North Lateral deposit juncture between upper and lower portions. Scattered boulders of the lower moraines are characteristically very rounded, and feature extremely low relief; many are flush with the ground surface (Fig. 35). Weathering pans sculpture most boulder surfaces of the eastern crest. Alternately, boulders of the upper crest are angular to moderately rounded and lack weathering pans. Two examples of exten sively disintegrated elephant-hide texture were encountered in the area just east of the second firebreak. Prominent mafic inclusions exist on the lower crest and are absent on the younger till. 69
Figure 35. Highly weathered boulder of low relief located on the lower North Lateral
CHAPTER IV
DISCUSSION OF RESULTS
A sequence of figures can be used to summarize results of age discrimination techniques applied to the Pine Creek glacial sequence. Preservation of original moraine morphology is time-dependent. Ex tended exposure to denudational agencies generally results in lower and broader crests. Figure 36 illustrates cross-sectional profiles of moraine crests that represent separate glacial advances as defined by spatial interrelationships. The vertical exaggeration is 2:1. Profile A-A• depicts the sharp-crested Inner South-east Lateral. The North Lateral crest, found at the same elevation as the Inner South east Lateral, is more massive and exhibits greater width than its southern counterparts. In profile B-B• the crest of the Outermost South-east Lateral tapers into a narrow ridge. The gradual slope ex tending from the Inner South-east Lateral crest is met by a steep em bankment north of Pine Creek. Profile c-c• intersects recessional moraines, characterized by the extensive inside slope of the Inner South-east Lateral. The North Lateral crest is sharper than indicated in the preceding profile. Contrasting with the North Laterals smooth form, the bulky outer slope of the South Lateral is a striking feature in profile D-o•. The amount of relief shown in this profile is also noteworthy.
ro 71
Figure 36. Moraine crest profiles. T marks the location of Pine Creek. Vertical exaggeration is 2:1 ••• •• •• •• ••••••••••• ··. •••••••••••••' .. ····· •• •• •• •••• •• •••• A
•• •••••• •••••••• • •• ...... ·.. •••••• '•• .. ..•• •• ~• •••••• •• ~ ...... ~ ~ B ••• s'
•••••••••••• • •• ••••• •• •...... •• ' •. .• ... •• •• ..... •• ••. c ··· c' •••••• • •• •• •• •• •• / ~ . . •• •• •• ••• •• • ••• ••• •• ••• • •• • • •. .• •~ ~ ~ ~, . o' ••• •• ••• 0 .· ·~· I 72
Frequency of Surface Boulders A compilation of boulder frequency data indicate distinct group ings (Fig. 37). Counts are clustered on the Outermost South-east Lateral and lower North Lateral, where boulder frequencies are low, although there is some overlap. A wide spread in boulder frequency is exhibited by the Inner South-east Lateral, South Lateral, and upper North Lateral. Very little distinction can be made between deposits, although there is a tendency for higher boulder frequency on the South Lateral.
Granite Weathering Ratios The boulder frequency technique lends supportive, but not defini tive evidence for time stratigraphic subdivisions of a glacial sequence. A more precise demarcation of an individual advance can be determined utilizing granite weathering ratios. This is a most sensitive technique, especially in areas of relatively homogeneous lithology. Granite weathering ratios are the most consistently reliable criterion employed for till deposit age-discrimination at Pine Creek. In Figure 38 the percentage of fresh boulders, determined by granite weathering ratio counts, is plotted against cumulative frequency of fresh boulders on arithmetic probability paper. Counts from the upper and lower North Lateral are treated separately. Four distinct weathering stages are indicated by the grouped data. Statistical analysis of granite weathering ratio counts substan tiates the validity of stratigraphic subdivisions established in Figure 38. The Mann-Whitney U test was used to test data from individ ual moraine crests to determine whether samples were from the same 73
Figure 37. Boulder frequency counts on the Outermost South-east Lateral, Inner South-east Lateral, South Lateral, upper and lower North Laterals. Each dot represents one count. --too
X
-240 X X xxxx XX 0
J( -280
0 '' 00 0 -160 00
·x 0
)( X -120 0 ' 0 ' X 0 X vv 0 -88 v v v vv vvv vvv v v 0 vvv vv ...... -40 ...... •. -o 74
Figure 38. Cumulative frequency of fresh boulders plotted on arithmetic probability paper. Data from the Outermost South-east Lateral, Inner South-east Lateral, South Lateral, upper and lower North Laterals.
Figure 39. Supplemental granite weathering counts combined with previous counts for data comparison with Figure 38. Data plotted on arithmetic probability paper. 99.99 - v Outermost South-east Lateral 0 Inner South-east Latera 1
99.9- X South Lateral 99.S- Lower ilorth Lateral ' Upper North Latera 1 99-
98-
95- v X 0 90- v
X v 8'l- 0 X v 0 X X t:: 70- v X w 0 ' u v X 0:: UJ 60 - v 0 a. v X UJ 0 ·> 50 - v X ~ 1- v 0 40- X < v 0 -' .. v ' 2 X 30 - v :su 0 X . v 20-. X v ' 0 X . v n- X
0 5 -. v X
2 -· 1 -
I I I I I I I I I I 0 10 20 30 40 50 60 7'J 81) 90 100
PPKEtlT FP.ESH 75 population. The Mann-Whitney test is one of the most powerful non parametric tests (Siegel, 1956, p. 116). This test was selected in place of the Student•s t because no assumption need be made concerning normal distribution of data. The null hypothesis (Ho) to be tested here is that granite weathering ratio samples have the same distribu tion, with no statistically significant difference between deposits. In a geomorphic sense this means that there is no age difference between deposits. The alternative hypothesis (HA) is that the samples come from two different populations. Geomorphically, nonrejection of HA indicates a statistically significant difference in the percentage of fresh boulders on the two till deposits. A one-tailed test is used because HA can be stated in such a way that the direction of difference is indicated (i.e., younger till will have more fresh boulders). Application of the Mann-Whitney test requires rejection of Ho as opposed to HA at the .01 significance level when the following deposits were tested: 1) Outermost South-east Lateral and Inner South-east Lateral, 2) Inner South-east Lateral and South Lateral, and 3) Outermost South-east Lateral and lower North Lateral. These statistical tests indicate that there is a statistically signi ficant difference between granite weathering ratios, and thus ages of their associated tills. Tests of the South Lateral and upper North Lateral do not reject Ho at the .05 significance level, indicating that samples are from the same population. To obtain an unbiased opinion and to insure that the correct field procedures were being employed, I took supplemental granite weathering counts at random spots along crests of the Outermost 76
South-east Lateral and North Laterals with the assistance of Dr. J. H. Birman. A slightly different procedure was used. Boulders larger than 0.30 m (1 ft) in diameter were tested for weathering by an observer who walked the crest. A call of 11 fresh 11 or 11 Weathered 11 from the ob server was noted by a recorder, who stopped each count at 100 boulders. The principal advantage in using this method is that of conserving the time normally taken to mark out a plot. The results of our field studies are combined with previous counts and plotted against the cumulative percentage of fresh boulders. Figure 39 is a transparent overlay for data comparison with Figure 38, illustrating that despite the implementation of slightly modified field techniques, the data maintained distinct groupings consistent with the original field methodology.
Boulder Morphology Each moraine crest, judged to be an individual deposit because of its physical relationship to the other crests in the glacial sequence, displays unique weathering characteristics. Some of these character istics are quantifiable, which lends supporting evidence to the investi gator's 11 feel 11 for the crest's character. However, the various classifications under the heading Boulder Morphology (e.g., boulder shape and relief, weathering pans, and granular disintegration) are mainly character impressions gained and recorded while walking the crests.
Interpretation The following hypothesis for the Pine Creek glacial sequence is 77 based exclusively on field observation: 1) the oldest remaining remnant of glacial till is located on the lower North Lateral crest. The lobe form that exists today may be a composite of more than one glacial advance. A suggestion of three topographically elevated areas can be discerned from aerial photographs and the topographic map~ however~ they are too subdued to be defined as crests. Erosion or subsequent glacial deposition has erased evidence of the paired lateral. 2) the next succeeding glacial stade is represented by the Outermost South-east Lateral; another unmatched crest that took a slightly different course from its predecessor. The up-valley extent has been overridden and partially buried beneath the more recent Inner South-east Lateral and South Lateral advances. The outliers extending beyond the South Lateral's outer slope (See page 54~ above) are all that remain of the upper crest. This observation from aerial photographs has been supplemented with field examination. Large numbers of 11 Water-worn 11 cobbles and boulders fill the saddle areas between outlier crest points~ an indication of meltwater spillways. The solitary lower crest stands as the most conspicuous evidence of this glacial advance~ its preservation primarily dependent upon the directional change taken by subsequent advances. 3) a glacial readvance is indicated by positioning of the Inner South-east Lateral, which also took a diversified route. The Inner South-east Lateral's counterpart is faint but visible on the inner face of the North Lateral. The north flank has been trimmed severely by erosion, destroying all but a trace, discernible on aerial photographs. A large meltwater channel transects both the upper crest of the Inner South-east Lateral and the crest of the Outermost South-east Lateral. Perhaps it is the result of streams emerging from the receding glacial ice associated with the South Lateral and its recessionals. 4) three factors indicate that the South Lateral is a product of separate glaciation rather than one of glacial fluctuation: a) crests of the Inner South-east Lateral and South Lateral trend in discordant directions (Fig. 40}. b) weathering characteristics of the two deposits are distinctly different. c) the massive bulk of the South Lateral contrasts with the size of the Inner South-east Lateral. The large mass, in all probability, stems partially from overriding debris deposited in earlier stades. The corresponding relief of the North Lateral~ which
79
is a composite of successive stades, helps to explain the South Lateral•s bulk as a result of more than one glaciation. The South Lateral, recessionals, and small inner crest are all associated with a single glaciation. The recessionals and inner crest represent a temporary equilibrium condition of the retreating glacier. Corresponding recessional segments, forming morainal loops, are visible on the North Lateral. The most clearly defined matched crests in the Pine Creek glacial sequence are the small moraines located on the inner face of both North and South Lateral. It was initially anticipated that these deposits represented a separate glacial advance. However, this theory was not supported by semiquantitative techniques, which indicate a weathering stage similar to the upper North Lateral and South Lateral. 5) the upper North Lateral crest is composed of debris from four stades, associated with the lower North Lateral, Outermost South-east Lateral, Inner South-east Lateral, and South Lateral. Evidence of the latter two stades remain. Much of the glacial record is concealed by successive deposition or removed by erosional and fluvial activity. Kesseli (1941) postulated that glacial directional changes were primarily due to position of interglacial creeks. No attempt is made in this investigation to interpret events which led to changes of glacial course at Pine Creek. CHAPTER V
CORRELATION OF PINE CREEK WITH OTHER SIERRA NEVADA EAST SLOPE GLACIAL DEPOSITS
The separate and discontinuous nature of alpine glacial deposits from canyon-to-canyon limit the application of stratigraphic correla tion through mapping. Absolute dates have been obtained and correla tions made in several Sierra Nevada east slope locations through radiometric techniques, however the range of error is significant, and radiometric techniques require stratigraphic contact between dateable volcanics and glacial tills. Reliable correlation of till deposits from canyon-to-canyon, therefore, is based on relative weathering characteristics. Sharp (1969, p. 69) suggested that semiquantitative data be interpreted by consideration of the spacing between sets of sequential data rather than comparison of absolute values. Table 5 summarizes boulder frequency counts taken in several eastern Sierra Nevada areas, listed geographically from north to south. A range of boulder frequencies is indicated for each glacial advance within a valley, although a canyon-to-canyon comparison would be misleading, as the values vary considerably. However, the interval between values in the series of data is comparable and is indicative of separate and distinct stades. Weathering ratio means from several Sierra Nevada east slope crests of Tioga age are tabulated with similar data from Pine Creek
80 81
TABLE 5
COMPARISON OF BOULDER FREQUENCY COUNTS FOR SEVERAL EASTERN SIERRA NEVADA LOCATIONS TIOGA TENAYA TAHOE PRE- TAHOE
Sharp 19 72 135 li 3 100 Lon·er P.obinscn Cn~ek (110-150)* (76-126) (76-124) 6 m X 30 ~ (20 ft X 100 ft) plot (£8i•* (57) (50) ------·------sr.a r;> 1·n2 210 135 83 Between Su~·•·-£·r'i V:ea..-Jc·~s and ?.cbinsur. Cr.~r:k 6 w X 30 ~ (2J ft X 100 ft) plot { 11):>) (68) (42)
Shar~ ar,d 9ir-·en 19S3 200 160 60 East s iCe vf fie:::>i r.son Crt>~~ at U~pcr Su·Ter-: ~ Sh-)r;l 1972 p? l-\4 105 L0~e""" Green ~ ref:k ( ~2S-22·)) (~:S-2~YJ) (s:·,-170} 6 m 1. 30 ;:1 {70 f: X 1-:yj f~) pi(.t { ~6) P'-i (S3) Sharp al"d Gir··.. Hi 19t.3 310 135 95 E3~t of Srefn Cr~~~ 6 1:1 _'( 30 rt1 {£;) ft '1. lGC ft} plot (155) {<;8) {48) Sharp 1972 lf.') 128 120 Vt r·...-_: in 1,3 Cn~t·i-~ (120-:?£0) (10~-EO) _(2'>-1Hl) 6 17j X 30 r,l !?.0 ft X 100 f~) plcot <~::a} (64) (60)_ Sharp 13(9 253 192 ~3 1~-t?: r Cr~:e~. (20'1--305) (E'-l-225) 6 r:1 1. 30 r.1 {20 ft. X 10'} ft) ~1vt ( 132) {96) - --~htl-~P--ar~-<1-B 1-J:".:-.o)~_1_i6_1 ______130 115 60 Bl G~·~y Cc.nJl''' 6 n X 30 ~ :zo ft X 100 tt: ~lot (ISJ) (90) (!>8) (Jt)) r.ono P.<.~:.! n Shar-,:. 1~(,9 226 100 Cc.nv·; o::t La~e (140-3~0) ( €0-150) 6 !q X 38 m (20 ft X 100 ft) ~lot (1 12.) (SO) Sharp ·1·:,s3 i·:_i\) l47 Tobac.c.0 I i l• t ( i3J-7t0) (60-260) f• \ 6 X 30 (?0 ft X 100 L I p~ot (9H) {7~) ---·------"' "' F1-~ishet· ~ ·~-o·;· 37 37 18 Coyote FLlt (26-50) (12-61) (~2-28) (5- 10) 61 m (2GO ft} le~:;th ( 13S) ( 185) (90) (2~-~.o) Fleisher 1?57 35 31 23 14 Bcket· Cn~e~- (25-49) (18-~2) (H-32) 61 m (2C•O fL) len9th ( 175) ( 155) ( 115) (70) Fleisher 1957 5') 43 22 14 Big Pine Crcf'k (27-133) ( 13-87) (9-33) 61 1:1 (200 ft) len~th (295) (215) {110)*** (70) ------* ran·:.;e ** con~ert~d to t~c Vdl_a t~at would be obtained from a 3m X 30 ~(10ft X 100ft) plot *** To~.oe land Tah;;~ II ~t£:~ r.c: diffen:nti.::L'd on the basis cf bJ:.. djet~ frequ£ncy 82 (Table 6). Although percentages vary considerably, the grouped data differs markedly from fresh boulder counts reported on Tenaya and Tahoe crests (Tables 7 and 8). Conclusions It is concluded from data presented in the previous chapters that there is evidence of four distinct Pleistocene glacial advances in the till deposits extending beyond Pine Creek canyon. Table 9 summarizes the conclusions of this investigation, which differ from the conclusions of Bateman (1965) in which he recognized four ages of deposits; identi- fied as Old Tahoe, Tahoe, Tioga, and Young Tioga. Age-assignments made for the Pine Creek glacial sequence on the basis of semiquantita- tive data follow closely the descriptions of Sierra Nevada glacial deposits found in Table 2. Figure 41 depicts the differences in loca tion and age-assignment attributed by Bateman (1965) and those mapped in this examination of the Pine Creek glacial sequence. Evidence that the lower North Lateral can be identified as a Mono Basin aged deposit is supported by the following points: 1) Mono Basin is characterized by a definite morainic form. 2) Mono Basin deposits are usually less extensive and voluminous than Tahoe deposits. 3) semiquantitative techniques support a pre-Tahoe age-assignment. 4) if the Bishop tuff underlies Round Valley, as indicated by Bateman (1965, pl. 5) (Fig. 6), any surficial deposit must be younger than Sherwin age, as Sherwin till deposits have been buried by the tuff. The stratigraphic relationship of the Bishop tuff with the Pine Creek glacial sequence puts an absolute age limit of 700,000 years (Dalrymple, and others, 1965} on the deposits. Differences of opinion exist over whether the Mono Basin glaciation is correlated with early Wisconsin or older mid-continental deposits. It 83 p ' TABLE 6 COMPARISON OF TIOGA AGE WEATHERING RATIOS WITH PINE CREEK DATA B1 ackv1e 1der 1931 (90-10-0) Binnan 1964 East Slope 90: 10* Grant Lake 69:31 Sharp 1972 Sharp 1969 Lo\,•er Robinson Convict Lake 87:13 Cr·eek· 77:2_3 Sharp 1972 Birman 1964 Between Summers Rock Creek 64:36 t·1eadows and Robinson Creek 64:36 Sharp 1972 Robinson 86:14 Lower Green Creek 87:13 Pine Creek 84:16 - Sharp 1972 Rahm (from Vi t•gi ni a Creek 89:11 Fleisher, 1967)· Bishop Creek 98:2 Binnan 1964 Fleisher 1967 LeeVining Canyon 67:33 Coyote Flat 83:17 Shat·p and Birman Fleisher 1967 . 1963 Baker Creek 67:.33 Walker Creek . (Sawmill and Bloody Canyons) 90:10 ·- Sharp 1969 Fleisher 1967 Walker Creek 91:9 I Big Pine Creek 73:27 * fresh:weathered 84 TABLE 7 COMPARISON OF TENAYA AGE WEATHERING RATIOS WITH PINE CREEK DATA Blacb1el der 1931 Birman 1964 East Slope ... 1Grant Lake 49:51 Shar·p 1972 Sharp 1969 Lm~er Robinson Convict Lake ... Creek· 4·3:57* ---- Sharp 1972 Birman 1964 Between Summers Rock Creek 53:47 ~1eadows and Robinson Creek 65:35 I Sharp 1972 Robinson Lower Green Creek 53:47 Pine Creek 56:44 -----·· Sharp 1972 Rahm (from Vir-ginia Creek 86:14 Fleisher, 1967) Bishop Creek ... Birman 1964 Fleisher 1967 Lee Vining Car,yon 52:48 Coyote Flat 50:50 Sharp and Birman Fleisher 1967 1963 Baker Creek • 47:53 Walker Creek (Sa~Gill and Bloody ~ Canyons) 50:50 Sharp 1969 1. Fleisher 1967 Wa 1kel' Creek Big Pine Creek 50:50 11 -t-·fresh :\-Jeathered 85 TABLE 8 COMPARISON OF TAHOE AGE WEATHERING RATIOS WITH PINE CREEK DATA Bl achJe 1der 1931 . (30-60-10) Bi nna·n 1964 (Sherwin?) East Slope 30:70* Grant Lake 4:96 Sharp 1972 Sharp 1969 Lower Robinson Convict Lake 53:47 Creek 26:74 Sharp 1972 Binnan 1964 Bet\veen Summers Rock Creek 32:68 Neadows and Robinson Creek 58:42 - --- ·------Sharp 1972 Robinson Lower Green Creek 36:64 Pine Creek 26:74 Sharp 1972 Rahm (from Virginia Creek 68:32 Fleisher, 1967) Bishop Creek 41:59 Binnan 1964 Fleisher 1967 LeeV1ning Canyon 22:78 Coyote Flat 22:78 ----- Sharp and Binnan Fleisher 1967 1963 Baker Creek 22:78 Wa 1ker Creek . (Sawmill and Bloody Canyons) 20:80 ~ Sharp 1969 Fleisher 1967 ~la.lkel' Creek 52:48 Big Pine Creek 25: 75** * fresh:weathered ** Tahoe I and Tahoe II are not differentiated on the basis of weathering ratios 86 TABLE 9 PINE CREEK GLACIAL SEQUENCE AGE-ASSIGNMENTS GLACIATION LOCATION AGE CRITERIA Tioga South Lateral Well-defined, sharp, narrow crest. Ground surface littered with cobbles. Boulder frequency median 224 (93-391). Granite weathering ratio median 91 percent fresh (48-97). Boulder morphology: unweathered loo~ing, angular, high-relief; no weathering pans or elephant-hide texture; surficial mafic inclusions. Tioga upper North Boulder-strewn crest. Boulder frequency median 157 Lateral -(124-189). Granite weathering ratio median 86 percent fresh (82-92). Boulder morphology: angular to moderately rounded; no weathering pans or elephant-hide texture; surficial mafic inclusions. Tenaya Inne\· Sou~h Morphologi<:al variatior. on crP.st. Ground surface east Lateral cover2d with s;rlall cobbles and coat·se c:rus. Boulde\" frequency median 161 (59-187). Granite weathering ratio median 59 percent fresh (34-65). Boulder morphology: angular to moderately rounded; few weathering pans and no elephant-hide texture; minimal mafic inclusions. Tahoe Outermost South Crest broad, well-formed ·and dissected by rills and east Latel·al gullies. Boulder frequency median 64 (45-87). Granite weathering ratio median 28 percent fresh (11-34). Boulder morphology: rounded; large weathering pans and elephant-hide texture developed on many boulders; mafic inclusions. Tahoe South Latera 1 Irregularly-spaced spurs composed of subtle crests 0utliers dissected by channels or gulJies. Crests, linked by an· imagi na 1·y 1 i nE:!, can be extended a 1ong the south slope of the Si!Jth Lateral to join the Outermost South-east Lateral. Large numbers of water-worn cobbles are found in the channels. f.';Q'lO Bas in lower North Broad, subdued, splayed-out crest. Ground surfd::e Lateral covered with fine g1·us and soil. Large areas cevoid of boulders and cobb 1es. Boulder· frequency median 37 (14-67). Granite weathering ratio median B percent fresh (0-21). Boulder morphology: very rounded, extremely low-relief; weathering pans on most boulder surfaces; prominent mafic inclusions. 87 Figure 41. Glacial deposits of the study area as mapped by Bateman (1965), above, and as mapped by this investigation, below. • YOUNG TIOGA TIOGA • TENAYA • TAHOE OLD TAHOE MONO BASIN 88 is fairly certain that the Tahoe, Tenaya, Tioga complex is of Wisconsin age. BIBLIOGRAPHY Axelrod, D. I., 1957, Late Tertiary floras and the Sierra Nevada uplift (California-Nevada): Geol. Soc. America Bull., v. 68, no. 1, p. 19-45. Axelrod, D. I., and Ting, W. S., 1961, Early Pleistocene floras from the Chagoopa surface, southern Sierra Nevada: Univ. California Pubs. Geol. Sci., v. 39, p. 119-194. Bateman, P. C., 1945, Pine Creek and Adamson tungsten mines, Inyo County, California: California Jour. Mines and Geology, v. 41, p. 231-249. ----:-:-_1965, Geology and tungsten mineralization of the Bishop district, California: U.S. Geol. Survey Prof. Paper 470, 204 p., and plates. Bateman, P. C., and Wahrhaftig, Clyde, 1966, Geology of the Sierra Nevada, pt. 1 in Chap. 4 of Bailey, E. H., ed., Geology of Northern California: California Div. Mines Bull. 190, p. 107- 172. Birkeland, P. W., 1964, Pleistocene glaciation of the Northern Sierra Nevada, north of Lake Tahoe, California: Jour. Geology, v. 72, p. 810-825 ---=-=-- 1968, Correlation of Quaternary stratigraphy of the Sierra Nevada with that of the Lake Lahontan area, in Morrison, R. B., and Wright, H. E., Jr., eds., Means of correlation of Quaternary successions: INQUA (Internat. Assoc. Quaternary Research) Congress VII, Proceedings 8, Univ. of Utah Press, Salt Lake City, Utah, 631 p. Birkeland, P.W., Crandell, D. R., and Richmond, G. M., 1971, Status of correlation of Quaternary stratigraphic units in the western conterminous United States: Quaternary Research, v. 1, no. 2, p. 208-227. Birkeland, P. W., and Janda, Richard J., 1971, Clay mineralogy of soils developed from Quaternary deposits of the eastern Sierra Nevada, California: Geol. Soc. America Bull., v. 82, p. 2495-2514. Birman, J. H., 1964, Glacial geology across the crest of the Sierra Nevada: Geol. Soc. America Spec. Paper 75, 80 p. 89 90 Blackwelder, Eliot, 1931, Pleistocene glaciation in the Sierra Nevada and Basin Ranges: Geol. Soc. America Bull., v. 42, p. 865-922. Clark, M. M., 1967, Pleistocene glaciation of the drainage of the West Walker River, Sierra Nevada, California (Ph.D. thesis): Standford Univ., 130 p. Dalrymple, G. B., 1963, Potassium-argon dates of some Cenozoic volcanic rocks of the Sierra Nevada, California: Geol. Soc. America Bull., v. 74, p. 379-390. ---:--- 1964, Potassium-argon dates of three Pleistocene interglacial basalt flows from the Sierra Nevada, California: Geol. Soc. America Bull., v. 75, p. 753-758. Dalrymple, G. B., Cox, A., and Doell, R. R., 1965, Potassium-argon age and paleomagnetism of the Bishop Tuff, California: Geol. Soc. America Bull., v .. 76, p. 665-674. Fleisher, P. J., 1967, Glacial geology of the Big Pine drainage, Sierra Nevada, California (Ph.D. thesis): Washington State Univ., 128 p. Gaines, John. California State Univ., Northridge. Interview, October 1974. Kane, Phillip S., 1975, Glacial geomorphology of the Lassen Volcanic National Park area, California (Ph.D. thesis): Univ. of California, Berkeley, 224 p. Kesseli, J. E., 1941, Studies in the Pleistocene glaciation of the Sierra Nevada, California: Univ. California Pubs. Geography, v. 6, p. 315-362. Morrison, R. B., 1968, Means of time-stratigraphic division and long distance correlation of Quaternary successions, in Morrison, R. B., and Wright, H. E., Jr., eds., Means of correlation of Quaternary successions: INQUA (Internat. Assoc. Quaternary Research} Congress VII, Proceedings 8, Univ. of Utah Press, Salt Lake City, Utah, 631 p. Nelson, R. L., 1954, Glacial geology of the Frying Pan River drainage, Colorado: Jour. Geology, v. 62, p. 325-343. Pakiser, L. C., and Kane, M. F., 1965, Gravity study of Owens Valley, in Bateman, P. C., Geology and tungsten mineralization of the Bishop- district, California: U.S. Geol. Survey Prof. Paper 470, p. 191- 195, and plates. Putnam, W. C., 1962, Late Cenozoic geology of McGee Mountain, Mono County, California: Univ. California Pubs. Geol. Sci., v. 40, p. 181-218. 91 ' . Sharp, R. P., 1969, Semiquantitative differentiation of glacial moraines near Convict Lake, Sierra Nevada, California Jour. Geology, v. 77, p. 68-91. ---=--.1972, Pleistocene glaciation, Bridgeport Basin, California: Geol. Soc. America Bull., v. 83, p. 2233-2260. Sharp, R. P., and Birman, J. H., 1963, Additions to classical sequence of Pleistocene glaciations, Sierra Nevada, California: Geol. Soc. America Bull., v. 74, p. 1079-1086. Sheridan, M. F., 1966, Preliminary studies of soil patterns observed in radar images, Bishop area, California: U.S. Geol. Survey Technical Letter NASA-63, 5 p. Siegel, S., 1956, Non-parametric statistics for the behavioural sciences. McGraw-Hill, New York. Smith, G. I., 1968, Late-Quaternary geologic and climatic history of Searles Lake, southeastern California, in Morrison, R. B., and Wright, H. E., Jr., eds., Means of correlation of Quaternary successions: INQUA (Internat. Assoc. Quaternary Research) Congress VII, Proceedings 8, Univ. of Utah Press, Salt Lake City, Utah, 631 p. Strand, R. G., compiler, 1967, Geologic map of California, Mariposa sheet, Olaf P. Jenkins edition: California Div. Mines and Geology, scale 1:250,000. Thomas, Phil. State of California Division of Forestry. Interview, March 24, 1975. Wahrhaftig, Clyde, and Birman, J. H., 1965, The Quaternary of the Pacifi.c Mountain system i.n California, in Wright, H. E., Jr., and Frey, D. G., eds., The Quaternary of the-United States: Princeton Univ. Press, p. 299-340. United States Forest Service, 1972, aerial photographs: Project IN-04. United States Geological Survey, 1949, Mt. Tom Quadrangle, California: scale 1:62,500. , APPENDIX A GRr'\IN-SIZE RELATIONSHIPS DETERHINED BY L'\BORATORY ANALYSIS Ol!TE~t10ST S9UTH-EAST LATERII.L DEPTH SITE PAN +40 +30 +20 +0.750 -10 15 em ( 6 in) Plot 3 1.16 4.59 17.76 31.97 33.96 l 0. 14 30 em ( 12 in) Plot 3 3.72 9.08 20.43 22.52 31.06 12.89 15 em ( 6 in) Plot 5 2.88 13.25 42.65 23.70 10.71 6.43 30 em (12 in) Plot 5 2.62 6.49 42.91 22.06 16.40 9.25 15 em ( 6 in) Plot 9 10.30 10.82 23.79 24;12 20.43 9.93 30 em (12 in) Plot 9 4.15. 9.32 21.06 22.29 27.82 15.17 iS em ( 6 in) Plot ll 9.00 10.15 25.20 27.20 20.65 7.55 30 em (12 in) Plot 11 2.80 6.35 32.15 27.40 21.65 9.45 15 em ( 6 in) Plat 13 6.55 6.15 21.85 28.05 27.05 10.35 30 em ( 12 in) Plot 13 3.0S 6.35 28.00 30.50 24.65 7.10 15 em ( 6 in) Plot 14 6.50 8.24 25.30 28.40 22.00 9.26 30 em ( 12 in) Plct 14 4.95 9.70 33.15 30.95 15.70 5.50 15 em ( 6 in) Plot 15 2.03 9.55 43.10 25 .. 06 13.30 6.75 30 em ( 12 in) Plot 15 5.07 5.25 19.50 30.00 31.50 8.50 15 em ( 6 in) Plot 17 4.20 10.85 30.07 30.07 17.30 6.10 30 em ( 12 in) • Plot 17 9.60 16.25 22.25 21.15 20.05 10.35 .92 93 f INNER SOUTH-EAST LATERAL DEPTH SITE PAN +40 +30 +20 +0.750 -10 15 em ( 6 in) Plot 22 13.72 15.70 25.37 20.70 16.89 6.97 30 em ( 12 in) Plot 22 13:73 14.05 23.30 20.70 20.35 7.43 15 em ( 6 in) Plot 23 11 .Sl 13.69 24.90 22.58 20.10 6.49 30 em '(12 i !1) Plot 23 12.QO 14.05 25.16 21.94 19.18 6.89 15 em ( 6 in) Plot 26 7.60 10.00 28.71 21.85 21.74 9.60 30 em (12 in) Piot 26 8.05 7.55 24.20 24.77 25.70 9.25 15em(6in) Plot 27 7.80 11.15 27·.10 20.95 22.40 10.00 30 em ( 12 in) Plot 27 1.22 9.28 30.60 22.95 20.97 8.75 15 em ( 6 in) Plot 29 6.60 13.75 34.10 20.80 17.40 6.80 30 em ( 12 in) Plot 29 7.15 10.25 25.35 25.98 21.20 9.55 15 em ( 6 in) Piot 30 10.05 10.10 20.45 22. i 5 26.00 11.00 30 em (12 in) Plot 30 8.10 8.15 24.90 23.70 23.05 11 .40 15 em ( 6 in) Plot 31 5.98 7. 72 17.43 27;54 29.53 11.33 3Q em (12 in) Plot 31 3.04 9.58 31.17 24.20 23.98 7.65 15-:m(6in) Plot 79 7.70 . 16.65 30.50 20.80 16.20 8.05 30 em (12 in) Plot 79 10.40 12.10 23.50 21.00 19.90 11.70 -----· 94 , SOUTH LATERAL DEPTH SITE PAN +40 +30 +20 +0. 750 -10 15 em ( 6 in) Plot 33 3.70 14.60 31.60 23.90 18.00 7.60 30 em ( 12 in) Plot 33 5.90 6.20 18.70 24.80 27.30 16.70 15 em ( 6 in) Plot 34 1. 90 5.50 41.55 27.60 15.60 7.65 30 em (12 in) Piot 34 1.93 10.18 34.00 23.79 21.71 8.11 15 em ( 6 in) Plot 38 10.40 16.60 25.50 20.50 17.00 9.80 30 em (12 in) Plot 38 9.50 15.85 24.00 - 20.45 19.80 10.10 15 em ( 6 in) Plot 39 9.65 13.05 21.20 22.85 22.45 10.40 30 em {12 in) Plot 39 7.00 11.30 24.00 30.25 20.00 7.30 . 15 em ( 6 in) Plot 41 12.60 15.54 24.00 19·.60 i9.00 9.30 30 em ( 12 in) Plot 41 13.4C 16.50 26.60 20.00 15.50 8.10 15 em ( 6 in) Plot 44 6.40 11 .60 30.30 24.70 18.70 7.60 15 em ( 6 in) Plot 4G 15.75 13.80 20.55 21.50 18.55 9.50 30 em (12 in) Plot 46 8.80 13.05 23.10 26.45 21.50 6.95 15 em ( 6 in) Plot 48 23.20 12.70 16.20 19.10 18.20 10.10 30 em (12 in) Plot 48 16.70 11.45 15.80 20.80 23.30 11.70 95 r NORTH LATERALS DEPTH · SITE PAN +40 . +30 +20 +0.750 -10 15 em ( 6 in) Plot 50 6.42 9.19 18.50 21.87 31.32 12.61 30 em ( 12 in) Plot 50 7.06 9.37 19.10 23.17 28.82 11.65 15cm(6in) Plot 52 6. 31 12.98 29.19 42.90 2.22 5.77 30 em. (12 i_n) Plot 52 4.71 7.80 35.31 44.27 2.19 5.43 15 em ( 6 in) Plot 54- 5.85 10.11 28.25 25.80 22.06 1.60 30 em (12 in) Plot 54 6.21 10.56 24.44 44.85 3.45 10.25 15 em ( 6 in) Plot 58 4.82 10.25 30.37 21.53 21.02 11 .18 30 ern ( 1(' in) Piot 58 4.90 10.12 33.52 23.12 20.59 7.24 15 em ( 6 in) Plot 60 5.16 14.05 31.02 24.02 18.90 6.30 30 em ( 12 in) Plot 60 6.55 11.43 30.75 24.49 19.52 6.94 15 em ( 6 in) Plot 65 4.49 8.12 22.72 21.48 26.00 16.80 30 ern ( 12 in) Plot 65 6.89 11.03 24.02 23.33 24.69 9.40 15 em ( 6 in) Plot 66 5.55 12.30 32.20 26.55 17.10 6.00 30 em (12 in) Plot 66 5.45 12.40 32.00 27.10 17.60 5.35 15 em ( 6 in) Plot 68 4.70 9.00 23.40 23.30 25.00 14.40 30 em ( 12 in) P1ot 68 9.75 10.80 21.60 23.40 24.30 9.70 15 em ( 6 in) Plot 71 3.00 11.40 49.55 32.80 2.80 .45 30 em (12 in) Plot 71 3.85 12.20 43.70 32.40 6.50 1.20 15 em ( 6 in) Plot 72 8.30 11.25 18.70 21.5Q 29.35 10.60 30 em (12 in) r·tot 72 7.65 10.35 18.50 23.30 31.10 3.95 15 em ( 6 in) Plot 77 4.50 12.95 31.65 27.50 18.80 4.40 30 em (12 in) Plot 77 3.00 11.35 31.30 27.15 20.50 6.35 96 APPENDIX B CUMULATIVE PERCENTAGES OF SILT- AND CLAY-SIZE SEDIMENT DETERMINED BY PIPETTE ANALYSIS, PLOTTED ON ARITHMETIC PAPER vo 15 em ( 6 in ) Sample x ~ 30 em (12 i n) Samo le -100 -95 vo - 90 0 0 )( v.•X -85 Ji.x 0• - 80 X 'I - ]5 oi -20 6' v · -65 • - 60 -55 -5 40 50 62) 70. 80 90 1'J0