The Late Cenozoic Evolution of the Tuolumne River, Central Sierra Nevada, California

The late Cenozoic evolution of the Tuolumne River, central Sierra Nevada, California

N. KING HUBER U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025

ABSTRACT Rancheria Mountain suggests that uplift had ancient prevolcanic channel of the Tuolumne been underway for some time before the vol- River. The volcanic rocks also help to date that Erosional remnants of volcanic rock depos- canic infilling. This timing is compatible with channel and make its reconstruction useful for ited in a lO-m.y.-old channel of the Tuolumne evidence from the upper San Joaquin River. estimating both Sierran tilt and the amount and River permit its partial reconstruction. Pro- Hetch Hetchy Valley on the Tuolumne is a rate of postvolcanic incision of the Tuolumne jection of the reconstructed channel west to much "fresher" glaciated valley than is River. Comparisons can then be made with sim- the Central Valley and east to the range crest, Yosemite Valley. Hetch Hetchy was filled to ilar estimates from the upper San Joaquin River. together with several assumptions about the the brim with glacial ice as recently as All data in this study were derived from topo- position of the hinge line and changes in 15,000-20,000 yr ago (Tioga glaciation), graphic maps at a scale of 1:62,500 with contour channel gradient, allows estimates of the whereas Yosemite Valley probably has not intervals of 80 or 100 ft, and all calculations amount of uplift at the range crest during the been filled for 750,000 yr or more (Sherwin therefore were made in United States customary past 10 m.y. At Tioga Pass, this amounts to as glaciation). Thus the upper reaches of Yosem- units. The results have been converted to metric much as 1,830 m, as compared to the 2,150 m ite Valley cliffs have been shaped by spalling units, but customary units are also retained, estimated in an earlier study for Deadman rather than by glacial scour and are much in parenthesis, for elevations, gradients, and Pass at the San Joaquin River 30 km to the more irregular than those in Hetch Hetchy. uplift calculations derived from them, to facili- south. Comparison of the geometry of these tate comparison with the maps and verify river systems leads to the conclusion that 10 INTRODUCTION calculations. m.y. ago an ancestral range of hills occupied the present site of the Sierran crest, and, al- Many studies have demonstrated that the LATE CENOZOIC VOLCANIC though of relatively moderate relief, it was a Sierra Nevada was uplifted during the late ACTIVITY barrier to westward drainage even before late Cenozoic to form the present range (for exam- Cenozoic uplift. At that time, the San Joaquin ple, Lindgren, 1911; Christensen, 1966; Huber, From about 20 m.y. ago to about 5 m.y. ago, River was apparently the only river flowing 1981), the central and northern Sierra having vast volumes of volcanic material were erupted westward across the range from well south of been tilted westward as a relatively rigid block from a belt of volcanoes near what is now the Mount Whitney north to Sonora Pass. The hinged near the eastern margin of the Central Sierran crest north of Yosemite National Park Tuolumne River evidently never extended Valley of California (Fig. 1). A recent study of (Durrell, 1966; Slemmons, 1966). During this east of this range. the late Cenozoic evolution of the San Joaquin late Cenozoic volcanism, the Sierra Nevada Comparison of the ancient channel with River basin within the Sierra indicated that up- north of Yosemite was virtually buried by lava the modern channel of the Tuolumne River lift of the range may have been underway by 25 flows, tuff, and lahars. The volcanic material permits analysis of the later evolution of the m.y. ago, but at a relatively low rate; the uplift traveled as far as the western Sierran foothills river system and the development of Hetch rate increased with time and may still be increas- and the Central Valley. Some of it traveled south Hetchy Valley and the Grand Canyon of the ing (Huber, 1981). over the present drainage divide from the Stanis- Tuolumne. At Rancheria Mountain, where The Tuolumne River is the northernmost of laus into the Tuolumne drainage basin. Three the volcanic "dam" in the ancient channel the major rivers draining the west slope of the separate units of this volcanic extravaganza— was highest, the river was forced to shift lat- Sierra Nevada whose course was not totally dis- lahar, a latite lava flow, and a welded tuff— erally southward around the dam and adja- rupted by the voluminous lahars and other vol- successively flowed down the valley of a cent to the volcanic infilling, and start its new canic rocks that buried most of the northern south-flowing tributary of the ancestral Tuo- channel in granitic bedrock. Near Rancheria Sierra. I have found no evidence for any vol- lumne River and into the main channel in the Mountain, as much as 1,525 m of new chan- canic disruption of the eastern third of the main vicinity of Rancheria Mountain northeast of nel incision has taken place in the past 10 trunk of the Tuolumne, and it remains in its Hetch Hetchy (Figs. 2,3,4). The latite flow and m.y., and the modern channel is about 915 m original channel. The western two-thirds, al- welded tuff have not been preserved beyond the lower than the abandoned channel. An unde- though shifted laterally, follows closely the pre- vicinity of Rancheria Mountain, and their origi- termined amount of this downcutting was volcanic channel for most of the distance to the nal extent is conjectural. Erosional remnants of from glacial erosion. Central Valley. the lahar are evidence that it flowed at least 51 The Tuolumne river system provides no di- Erosional remannts of the volcanic sequence, km farther west (Fig. 4). Other remnants east of rect evidence for timing the onset of uplift, particularly where underlying fluvial deposits Rancheria Mountain show that it was fluid but the shape of the lO-m.y.-old channel at are preserved, allow partial reconstruction of an enough to flow upstream along the main chan-

Geological Society of America Bulletin, v. 102, p. 102-115, 11 figs., January 1990.

102

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Figure 1. Generalized topographic map of the Sierra Nevada, illustrating the tilt-block nature of the central part of the range and the location of the major streams draining its western slope (adapted from Christensen, 1966). Contours in ft x 1,000.

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120°00' 119°30' 119°00'

Figure 2. Index map of the Tuolumne drainage basin and vicinity. Main trunk of the Tuolumne River emphasized by heavier line weight. Dashed lines are drainage divides.

nel at least 8 km above the junction with the in the vicinity of the present Clavey River. This The lava flow beneath the welded tuff on south-flowing tributary (Fig. 4). Because it is distinctive biotite-bearing tuff is similar in all Rancheria Mountain, described as latite by Dal- more widespread, the lahar is the key to tracing respects to Ransome's (1898) "biotite-augite la- rymple (1963), was subsequently designated a the course of the ancestral Tuolumne River. The tite," which is now included within the Eureka trachyandesite by Kistler (1973,1974). Trachy- latite flow and welded tuff, however, provide Valley Tuff (Noble and others, 1974). The dense andesite in the central Sierra Nevada tends to be stratigraphic and age controls. welding and abundance of biotite in the tuff at of local origin and of limited extent (Moore and The volcanic section on Rancheria Mountain Rancheria Mountain suggest that it is correlative Dodge, 1980). The rock at Rancheria Mountain was described briefly by Dairymple (1963), with the Tollhouse Flat Member, the lowest unit is very dark and dense and has tabular plagio- who also calculated a K-Ar age of 9.1 m.y. for in the Eureka Valley Tuff. The Eureka Valley clase phenocrysts typical of the Table Mountain the welded tuff (all ages cited here have been Tuff came from the Little Walker caldera east of Latite. A chemical analysis of a sample from recalculated to 1977 constants). An additional Sonora Pass and about 45 km north of Ranch- Rancheria Mountains (Kistler, 1974) compares age determination of 9.2 m.y. was obtained by eria Mountain (Fig. 2). Eleven K-Ar ages pre- favorably with analyses of the Table Mountain Dalrymple (1963) on similar tuff on Jawbone sented by Noble and others (1974) for the Latite (Dodge and Moore, 1981). After visiting Ridge (Figs. 2, 4) that apparently flowed south Tollhouse Flat Member include Dalrymple's Rancheria Mountain, I agree with Dalrymple's along another tributary of the Tuolumne River and give an average age of about 9.5 m.y. designation of the rock as latite and his córrela-

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Figure 3. Ancient channel of the Tuolumne River exposed along the western bank of Piute Creek at Ranchería Mountain (Fig. 2). The river flowed westward away from the viewer into the V-shaped notch cut into granite (center of the photograph). Stream gravel in the channel was later buried beneath volcanic lahar. The dark, horizontal zone about halfway up the central part of the V is brush marking the top of a cliff of highly indurated lahar that extends down behind the large trees below it; the gravel section is hidden behind those trees. The channel cross section is now exposed by erosion along the west side of Piute Creek. This ancient channel was first described by H. W. Turner (1901), who took this photograph.

tion of it with the Table Mountain Latite, which implies a source for the lava flow in the general Sonora Pass area some 40 km north of Rancher- ía Mountain (Fig. 2). Dalrymple (1964) calcu- cia presumed to be related to the Relief Peak Creek about 5 km north of where that tributary lated a K-Ar age of 9.2 m.y. for the Table lahars has been dated at 10.5-15 m.y. (Morton creek flows into the present Tuolumne River Mountain Latite near Sonora (Fig. 2). Because and others, 1977). The exact relationship of (Fig. 3). Turner's (1901, p. 540) description is the welded tuff directly overlies the latite at these breccias to the Relief Peak Formation is worth quoting: Ranchería Mountain, I have adopted an age of unknown. If these ages are representative of an- ~9.5 m.y. for the two volcanic units jointly. Of desite in the region, then the andesitic lahars of To the west of [Piute] creek is an even better section of historic interest, H. W. Turner was the first to the Relief Peak Formation were erupted be- a lava-filled V-shaped channel, and in this case the mention the "compact lava" on Ranchería tween 15 and 10 m.y. ago. river gravels are to be seen perhaps 50 ft (15 m) in thickness at the bottom of the channel. Besides abun- Mountain and refer to it as latite (1901; also I suggest that the lahar on Ranchería Moun- dant lava pebbles, there are numerous pebbles of slate quoted by Lindgren, 1911), presumably based tain represents the uppermost part of the Relief and metamorphic lavas such as make up the mass of on his knowledge of the Table Mountain Latite Peak Formation. The formation now has a Mount Dana, and one pebble was found of epidotifer- near Sonora. thickness of about 915 m near its presumed ous sandstone, precisely like the rock of the summit of Dana. Since between this locality and Mount Dana source at Relief Peak; it seems reasonable that In the Sierra Nevada north of Yosemite, an- the bedrock series is all granite, it appears probable desitic lahars account for much of the late Ceno- the lahar on Ranchería Mountain resulted from that in Tertiary time, as now, the Tuolumne River zoic volcanic section (Slemmons, 1966; Noble one of the culminating eruptions from a volcanic headed near Mount Dana. and others, 1974). A lower sequence, the Relief edifice that had grown high enough to send Peak Formation, is separated from an upper se- flows southward to the Tuolumne River. Turner In a visit to this site, I did not find anything quence, the Disaster Peak Formation, by the (1901, p. 541) described an alluvial gravel rest- that I would call "lava pebbles." I do not know Stanislaus Group, which includes the Table ing on the lahar on Ranchería Mountain "and what Turner meant by this term, inasmuch as he Mountain Latite and the Eureka Valley Tuff. apparently capped by the compact lava latite also referred to "metamorphic lavas." Most The position of the lahar on Ranchería Moun- adjoining." I observed a similar relationship pebbles are of resistant metamorphic rocks, in- tain beneath rocks correlated with the Table north of Ranchería Mountain. He interpreted cluding numerous pebbles of hornfels similar to Mountain Latite and the Eureka Valley Tuff this gravel as representing "a stream of the vol- the rock on Mounts Dana and Gibbs. Granitic indicates that the lahar there must be part of canic period," but it need not indicate a signifi- pebbles are present, but not abundant, and in- the Relief Peak Formation. The source area for cant gap of time between the two volcanic units. clude hornblende granodiorite and porphyritic the Relief Peak Formation is considered by For my interpretation, I adopt an age of about Cathedral Peak Granodiorite, rocks which un- Slemmons (1966) to be in the vicinity of Relief 10 m.y. for this lahar, which I believe defines an derlie much of the Tuolumne River drainage Peak, some 32 km north of Ranchería Moun- ancient channel of the Tuolumne River. basin upstream from Rancheria Mountain. tain (Fig. 2). Their scarcity in the gravel suggests that at the The age of the Relief Peak Formation is TEN-MILLION-YEAR-OLD CHANNEL time of deposition the granitic terrane was bracketed by the age of about 9.5 m.y. for the OF THE TUOLUMNE RIVER deeply weathered and was contributing mostly overlying Table Mountain Latite and several de- grus rather than larger clasts to the drainage sys- terminations averaging 23 m.y. for the underly- The most critical exposure for defining an an- tem. At present, little more than a meter of ing Valley Springs Formation (Dalrymple, cient channel of the Tuolumne River is on the gravel is exposed beneath the lahar at this site, 1964). Northwest of Sonora Pass, andesite brec- east side of Ranchería Mountain facing Piute and the rest of the slope down to granitic bed-

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120°15' 38°00' 120°00'

0 5 10 15 KILOMETERS 1 I I I Figure 4. Miocene volcanic and fluvial deposits in the Tuolumne drainage basin and reconstruction of the Miocene stream channel. Distribution of the volcanic rocks shown is that of lahar of the Relief Peak Formation. Table Mountain Latite and Eureka Valley Tuff locally overlie the lahar in the vicinity of Ranchería Mountain, but outcrop areas are too small to show at map scale. Inset shows longitudinal profiles of modern and reconstructed Miocene channels projected onto a vertical plane striking N72°E. Arrows indicate lower limit of Tertiary deposit. G indicates presence of fluvial gravel; AM, Ackerson Meadow; NT, northern tributary to Miocene Tuolumne River. Geologic data from Turner and Ransome (1897), Kistler (1973), Dodge and Calk (1987), G. B. Dalrymple (1978, written commun.), and Clyde Wahrhaftig (1982, written commun.) (Note overlap in center.)

rock is covered by talus and slopewash. Turner on the east, resulting in a tilting of the range presence of isolated erosional remnants of lahar (1901, p. 541) reconstructed the old channel westward." (Fig. 4); no alluvial gravel is exposed. For westward from Piute Creek and concluded that From the vicinity of Piute Creek westward another 16 km westward, alluvial gravel ex- "the present grade of the Neocene channel must for about 40 km, the approximate course of the posed beneath the lahar more closely defines the have been brought about by a differential uplift ancient Tuolumne River is traced solely by the river's course (Fig. 4). This gravel has been hy-

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120°00 7

Figure 4. (Continued).

draulically mined at several points, providing old Tuolumne channel. Lindgren (1911), how- major drainage (Jones, 1976). The deposit, good exposures of deposits that are made up ever, postulated that it continued generally however, is unsorted, contains large angular chiefly of locally derived pebbles of siliceous westward to Chinese Camp (Fig. 4), a distance blocks, has only locally derived material, and metamorphic rocks and vein quartz. Granitic of about 40 km, where Tertiary gravel is next has a very high gradient, even allowing for later pebbles are uncommon and limited to aplite and encountered. tilting of the range. It may be some form of a other felsic varieties resistant to weathering. From just east of Piute Creek to the Sierran debris flow (Huber and others, in press). I know The old channel lies on the north side of the crest, there is also a lack of Tertiary gravel or of no evidence to suggest that the Tertiary Tuo- present Tuolumne River canyon westward from lahar to indicate the location of the old Tuo- lumne River flowed in any but its present course Ranchería Mountain, crosses the canyon about lumne channel. A deposit near the head of the east of Piute Creek. The presence of material in 3 km west of Mather, and then remains on the Dana Fork of the Tuolumne River (Fig. 2) be- the Tertiary gravel at Rancheria Mountain that south side of the canyon as far as it can be traced tween Mount Dana and Mount Gibbs was was presumably derived from Mount Dana rein- to a point about 6.5 km northeast of Groveland termed a Tertiary "indurated conglomerate" by forces this view. (Fig. 4). From this point west, no Tertiary gravel Kistler (1966). This deposit has led at least one Lindgren (1911, p. 218) commented that or lahar is present to indicate the location of the writer to infer that it was the site of a former "one striking fact is that the present Tuolumne

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Mows closely, except in its lower course, the makes comparison between the two stream valley of the Tertiary river." He correctly sur- courses easier. mised the reason for this, for unlike the situation Because meanders are eliminated in the pro- farther north, "this is due to the small amount of jection process, distances measured along the andesitic lavas [lahar], which simply followed the profile are shorter than those measured along the old valley downward without flooding the di- actual stream itself; therefore, gradients meas- vides or causing important stream diversion." ured along the profile are steeper than the actual The lahar is indurated and more resistant than gradients and more nearly reflect the regional the presumably weathered granitic rock that un- slope. For the stretch between Piute Creek and derlay most of the valley containing the ancient Buck Meadows, the modern stream (even as channel from the Piute Creek junction west- generalized) has meanders with slightly smaller ward. After damming, the ancestral Tuolumne radii than does my reconstruction of the ancient River apparently shifted southward within the channel (Fig. 4), and its gradient therefore is valley to cut down into the granite alongside the overestimated slightly more than that of the lahar (Fig. 5). The stream stayed on the south older channel. The projected profile is useful, side of the lahar from Piute Creek to a few however, to make channel comparisons at a kilometers west of Mather. Here it crossed the given linear distance upslope from the Central lahar that filled the old channel and from there Valley or other common point along the profile. stayed on the north side at least as far as Grove- A more important inference can be made land (Fig. 4). The apparent cross-over locality when the channel of the ancient stream deviates west of Mather is about where a tributary from markedly from the present regional slope. the southeast joined the ancient Tuolumne. Evi- Lindgren (1911) noted the anomalously low dence for this tributary consists of an outcrop of gradient of Tertiary channels trending at low lahar near Ackerson Meadow, about 4 km south angles to the Central Valley compared to those of Mather (Fig. 4), which I interpret as having of channels trending normal to the valley. He resulted from backflow up the tributary from the cited this as one of the most compelling argu- main channel. If this interpretation is correct, ments for uplift and tilt of the range, because then the Tuolumne River flowing along the Figure 5. Schematic diagram showing those segments at low angles would be least af- south side of the lahar in the main channel southward shifting of the ancestral Tuolumne fected by tilt and thus closer to their pre-tilt would have been directed into the arms of the River as volcanic lahar flowed from the north gradient. Recognition of this principle provides "lahar-Y" at the tributary junction, and the river into the ancient valley, damming it. The river an approach to estimating uplift and tilt, if suit- crossed over the main-channel lahar rather than then shifted laterally to flow along the south able segments of the ancient stream profile can be the segment of the lahar in the tributary (Fig. 5). side of the lahar, eventually crossing to the reconstructed. The new channel stayed on the north side of the north side upon reaching a Y in the lahar that An application of Lindgren's precept to the main-channel lahar westward beyond Grove- had been formed by flow up a tributary. ancestral Tuolumne River may provide some land but would have had to cross the old chan- (Sketch provided by T. R. Alpha.) constraints on estimates of uplift and tilt in the nel again if the old channel reached Chinese central Sierra at the latitude of the Tuolumne Camp. Lindgren (1911) suggested that the old drainage, although translating this concept into channel passed north of Hog Mountain, on the meaningful numbers is difficult. The ancient north side of the present Tuolumne, about 8 km Tuolumne River flowed southwest from Gravel east of Chinese Camp (Fig. 4). Although such a Range to Buck Meadows (Fig. 4), that is, almost course is reasonable, there are no Tertiary depos- elevations for the channel. One isolated locality directly down the regional slope, and the aban- its to document it. south of the main channel (near Ackerson Mead- ow) is probably associated with a channel of a doned channel presently has an average slope of tributary. At a few exposures, where the base of 20.8 m/km (110 ft/mi) over a distance of about STREAM GRADIENTS AND UPLIFT the lahar is concealed by glacial till, maximum 8 km. At Buck Meadows, the channel turns CALCULATIONS elevations are also indicated. West of Grove- about 65° to the northwest toward Corcoran land, reconstruction of the channel is con- Flat (Fig. 4). This reach of the abandoned chan- Using the Tertiary gravel and lahar deposits, a strained only by the assumption that the Tertiary nel has an average slope of about 9.5 m/km (50 longitudinal profile of the lO-m.y.-old stream gravel at Chinese Camp is associated with the ft/mi) over a distance of about 10 km. If the has been constructed from the Piute Creek area ancient Tuolumne River system, as postulated abrupt change in average gradient between the west toward Groveland (Fig. 4). The present by Lindgren (1911). two reaches at Buck Meadows is the result of elevation of the ancient channel is well con- The longitudinal profiles for the ancient Tuo- uplift and tilt of the range since the channel was strained in only two places—on Rancheria lumne and the modern stream (Fig. 4) were con- abandoned, this would amount to a tilt of about Mountain and in an 18-km stretch east of structed by projection onto a vertical plane with 11.4 m/km (60 ft/mi). Groveland, where stream gravels are preserved an azimuth of N72°E. This azimuth is about 15° Calculation of the amount of uplift at a beneath the lahar. Localities where the lahar more to the east than the regional slope of the specific locality, based on estimated increases rests upon granitic bedrock are assumed to be Sierra Nevada at this latitude, but it parallels the in stream gradient, requires some additional outside the main channel on adjacent valley general trend of both the ancient and modern assumptions—most importantly, the position of slopes, as was also surmised by Turner (1901). Tuolumne channels for the stretch from Piute the hinge line for tilting. For the Tuolumne tran- These localities, however, provide maximum Creek west to Buck Meadows (Fig. 2) and sect, I have placed the hinge line at the region-

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W2Z30" 119°15'00" 119W30"

I I I I I I 0 5 KILOMETERS 1 I I I I I

Figure 6. Tioga Pass area and headwaters of Dana Fork of the Tuolumne River. The present Sierran drainage divide is shown by a heavy, dashed line. A postulated earlier drainage divide is shown by a heavy, dotted line. Before capture by Lee Vining Creek, the basin containing Saddlebag Lake would have drained south through Tioga Pass to the Dana Fork of the Tuolumne River.

ally smoothed 152-m (500-ft) contour at the data from the Eocene lone Formation and on to late Cenozoic uplift of the range (Bartow, eastern side of the Central Valley, that is, about the lO-m.y.-old reconstructed stream profile. In 1985). 38.6 km southwest of Buck Meadows. In the the Tuolumne area, the 152-m (500-ft) contour At Buck Meadows, 38.6 km northeast of the San Joaquin River study (Huber, 1981), the also approximates the eastern limit of the lone assumed hinge line, the calculated uplift re- 152-m (500-ft) contour seemed to be the best Formation, which is composed of granitic- quired to increase a gradient from 9.5 m/km (50 hinge-line position, on the basis of pre-uplift derived sediment from "Sierran" lowlands prior ft/mi) to 20.8 m/km (110 ft/mi), an increase of

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11.4 m/km (60 ft/mi), is 440 m (1,440 ft). This tween the two transects. Calculations for both The calculated difference in uplift between amount of tilt, projected to the range crest, transects assume a rigid-block model. If warping Deadman Pass and Tower Peak (Fig. 2) is 669 would result in an uplift of 1,097 m (3,600 ft) at is involved, I assume that the effects would be to 1,053 m (2,195 to 3,455 ft), or 10 to 16 Tower Peak (Fig. 2), 96.5 km northeast of the similar for the two transects, in which case dif- m/km (54 to 84 ft/mi) northward along the hinge line, if tilting of the range occurred as a ferences between uplift estimates for them may range. If this difference were uniformly distrib- rigid block within the past 10 m.y. This estimate be more significant than the actual amount of uted, the uplift at the site of present-day Tioga of uplift is a minimum under the assumptions of uplift calculated. Except for an area west of Pass (Fig. 2) would have been 1,688 to 1,856 m the calculation, because it does not take into Buck Meadows, each transect is covered by (5,540 to 6,090 ft). Both the San Joaquin and account that some part of the slope of the stream modem 15-minute geologic quadrangle maps, Tuolumne calculations represent uplift since segment with an average slope of 9.5 m/km (50 and no significant late Cenozoic faulting has about 10 m.y. ago. At that time, the San Joa- ft/mi) must also be attributable to uplift. been recognized. quin River would have had an elevation of If the 440 m (1,440 ft) of uplift calculated for 1,052 m (3,450 ft) at Deadman Pass (Huber, Buck Meadows is subtracted from the present COMPARISON OF TUOLUMNE AND 1981), and the Tuolumne River, a minimum elevation of the ancient channel, that channel SAN JOAQUIN RIVERS elevation of 1,175 m (3,855 ft) at Tioga Pass, would still be 155 m (510 ft) higher than the using maximum uplift estimates. This difference present channel of the Tuolumne River adjacent The uncertain nature of the calculated uplift, is a minimum, however, because subtracting up- to Buck Meadows. This amount seems unreason- as described in the preceding section, should be lift from the present-day elevation at Tioga Pass able if the range had less relief 10 m.y. ago and if apparent Nevertheless, this and similar calcula- does not include any allowance for erosion at the Tuolumne River at that time was graded to tions from elsewhere in the Sierra may provide the pass during the past 10 m.y. The pass is about the same elevation in the Central Valley some constraints on attempts to reconstruct the presently more than 457 m (1,500 ft) below the as the modern river is today; in my calculations, late Cenozoic history of the range. Tertiary surface represented by Dana Plateau some 3 km to the east. I have assumed this postulated position of the In the upper San Joaquin, the lO-m.y.-old hinge line for tilt. If the ancient Tuolumne chan- stream channel was reconstructed from the Cen- The ancestral Tioga Pass was higher than an- nel near Buck Meadows 10 m.y. ago was at least tral Valley to the present range crest, permitting cestral Deadman Pass, despite the general eleva- as low in elevation as the present Tuolumne calculation of a "best" estimate of 2,150 m tional decrease northwestward along the Sierran channel, then an additional uplift of 155 m (510 (7,055 ft) of post-10-m.y.-ago uplift at Dead- crest. Deadman Pass lies on the only significant ft) would be required to bring Buck Meadows to man Pass (Fig. 2), rather than a range of esti- broad saddle on the central Sierran drainage di- its present elevation. This amount would trans- mates as at Tower Peak (Huber, 1981). It is vide between Mount Whitney, to the south, and late to a total uplift of 1,481 m (4,860 ft) at significant, however, that the higher of the esti- the north boundary of Yosemite National Park, Tower Peak and provide estimates varying by mates for Tower Peak is more than 610 m north of Tower Peak. This broad saddle reflects 384 m (1,260 ft; from 3,600 to 4,860 ft) for (2,000 ft) less than the one for Deadman Pass. the long history of "trans-Sierra" drainage for uplift at the range crest there. Tower Peak was In the central Sierra, where rotational uplift the Middle Fork of the San Joaquin River. The selected as a reference point on the Tuolumne seems to dominate, maximum summit eleva- river apparently flowed west through the site of transect because it is almost directly up the re- tions gradually decrease from the northern Deadman Pass until about 3 m.y. ago, when the gional slope from Buck Meadows and is the Kings River drainage to the northern Tuolumne channel was blocked by basalt flows, causing the same distance northeast of the assumed hinge drainage. This decrease in elevation would sug- headwaters east of the pass to be diverted south line as is Deadman Pass on the San Joaquin gest a decrease in total uplift from south to north into the already forming Owens Valley graben River (Huber, 1981), permitting comparison be- for this segment of the range. (Huber, 1981). That the ancestral drainage area

Ranchería Mtn South North Direction of 12000 r- Ancestral channel of the lahar (low — 12000 Grand Canyon of the Tuolumne River

I- Tuolumne River LU UJ at Pate Valley 2 8000 8000 O t<- >

4000 4000

NO VERTICAL EXAGGERATION

Figure 7. Geologic cross section at Ranchería Mountain showing present and ancestral channels of the Tuolumne River. Trp, lahar of Relief Peak Fm.; Ttm, Table Mountain Latite; Tev, Eureka Valley Tuff. View looking downstream.

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L 1 01 5I 1I0 KILOMETERS VERTICAL EXAGGERATION 5.2x Figure 8. Longitudinal profile of the Tuolumne River east of Hetch Hetchy, eliminating minor meanders. Above Tuolumne Meadows, both the Dana and Lyell Forks are shown. Piute Creek, tributary to the Tuolumne at Pate Valley upstream from Hetch Hetchy Reservoir, is also shown.

was of considerable size is indicated by the fact above. This conclusion lends some qualitative cision, possibly aided by a glacier or glaciers that the San Joaquin had sufficiently high dis- credence to the calculations even though the flowing eastward over a saddle in the former charge to maintain its course across the rising numerical values contain large uncertainties. crest. Before this capture, the Sierran drainage Sierra until it was cut off by the volcanic Although the Tuolumne River apparently divide would have been a few kilometers east of activity. never headed east of the present range, one of its the present one between Mount Dana and Ex- During its early history of trans-Sierra drain- forks may have headed east of Tioga Pass. The celsior Mountain, following a belt of resistant age, the San Joaquin River was partly incised trough containing Tioga Pass trends north-south metamorphic rocks over Dana Plateau, Tioga along its entire length as the incipient Sierra and projects directly up the valley of the upper Peak, and Tioga Crest (Fig. 6). The present Nevada was uplifted; the present channel is part of Lee Vining Creek toward Saddlebag abrupt drop of Lee Vining Creek below Ellery deeply incised up to the west side of Deadman Lake (Fig. 6). A stream profile down this upper Lake takes place at the eastern edge of this Pass. When the headwaters were diverted about creek and over Tioga Pass projects only 152 m metamorphic belt. A small area at the north end 3 m.y. ago, stream and glacial erosion were less below the pass, and the pass itself contains an of this postulated earlier drainage system was effective, and only part of the old channel west unknown thickness of glacial till. If upper Lee captured in a similar fashion by Mill Creek in of the pass was exhumed by removal of the Vining Creek once drained south through Tioga Lundy Canyon (Fig. 6). basalt that once buried it and deepened an addi- Pass, it was subsequently captured by the main Morainal deposits of the Tioga glaciation tional 177 m into bedrock (Huber and Rinehart, trunk of Lee Vining Creek during headward in- (latest Pleistocene) at Tioga Pass and south to 1967). In contrast to the San Joaquin, the Tuolumne River is deeply incised eastward only to a point several kilometers west of Tuolumne Meadows (Fig. 2). Eastward to the Sierran crest, the river meanders through upland meadows and up the broad low-gradient "Canyon" of the Lyell Fork, and also up the Dana Fork of the Tuolumne, which drains Dana Meadows southwest of Tioga Pass (Fig. 6). The Tuolumne River, which apparently had no trans-Sierra drainage, re- sponded to uplift with incision of its channel. Incision proceeded headward from the Central Valley, but major incision has not yet reached Tuolumne Meadows. The area immediately to the east of the Tuolumne drainage basin was being drained by the ancestral San Joaquin Figure 9. Cartoon of long profile showing the effects of the lahar dam on stream downcut- River. If the preceding scenario is true, then the ting. The new channel would be cut into granitic rock alongside the lahar (see Fig. 5), but the site of Tioga Pass would indeed have been lahar would establish the gradient for the new channel. Dashed lines indicate successive stages higher than that of Deadman Pass 10 m.y. ago, of channel downcutting as the knickpoint migrates upstream. The area immediately above the as suggested by the uplift calculations made knickpoint will not be incised until the knickpoint intersects the original channel (heavy line).

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Dana Meadows contain erratics of porphyritic Cathedral Peak Granodiorite. Outcrop areas of Cathedral Peak Granodiorite occur along the Dana Fork of the Tuolumne River west of Dana Meadows and also on the east side of the Sierran drainage divide on Mount Conness, west of Saddlebag Lake in the upper Lee Vining Creek drainage (Fig. 2; Bateman and others, 1983). A boulder train of metamorphic rocks that was deposited along the Dana Fork and derived from the Mount Dana-Mount Gibbs area indicates that ice from that area flowed westward down the Dana Fork (Clyde Wahrhaftig, 1988, written commun.). Thus, the Dana Fork could not have been a source for the Cathedral Peak erratics in Dana Meadows; they must have been derived from the Mount Conness area. Such erratics would have been delivered to the west side of a glacier moving south along upper Lee Vin- ing Creek, and their presence in Dana Meadows indicates that during the Tioga glaciation ice flowed south through Tioga Pass. The geometry of what appear to be medial moraines in and west of Dana Meadows at the juncture of this ice and that from Parker Pass Creek further sub- stantiates this conclusion (M. M. Clark, 1976; and 1988, written commun.). We do not yet know what fraction of the ice in the Saddlebag Lake drainage flowed through Tioga Pass, but at least by the time of Tioga glaciation, stream capture by Lee Vining Creek was sufficiently advanced to cause much of that glacier to fork and flow down Lee Vining canyon.

The overall evolution of the Tuolumne River system would not be greatly affected by the postulated loss of about 47 km2 of the upper Lee Vining Creek drainage by stream capture. Addi- tion of this area would, however, allow for fluvial and glacial transport and erosion across the site of Tioga Pass and explain, without the need for trans-Sierra drainage, why the pass is more than 305 m lower than the Tertiary erosion surface on Dana Plateau only 3 km to the east. In the preceding discussion of the evolution of the Tuolumne River system, emphasis is placed on the main trunk of the river that headed in its Dana and Lyell forks—an area critical to the postulate of past trans-Sierra drainage at this location. Such a postulate was advanced recently by Schaffer (1986), who suggested that a "Tenaya River," (his emphasis) existing since early in the Eocene, originated from lands east 0 1 2 3 4 5 MILES of today's range and flowed through the sites L— I 1 I 1 1 of today's Tioga Pass, Tuolumne Meadows, 0 1 2 3 4 5 KILOMETERS Tenaya Lake, Tenaya Canyon, and Yosemite 1 I I I I—I Valley. Schaffer (1986; see reverse side of his Horizontal scale map) further suggested that the headwaters of (Front-to-back scale foreshortened by 43%) this Tenaya River were subsequently captured Ice-surface contours in feet

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Figure 10. Oblique map showing Tioga-age glaciers in the Tuolumne drainage. View is tocene, although only a few of these glaciations toward the east-northeast. The main-trunk glacier flows from Tuolumne Meadows at upper can be documented by surviving morainal de- right down into the Grand Canyon of the Tuolumne where it is joined by a tributary glacier posits (Gibbons and others, 1984). During each from Piute Creek east of Ranchería Mountain (at the site of Pate Valley). West of Ranchería glaciation, an alpine icefield fed valley glaciers Mountain, the main glacier is joined successively by tributary glaciers from Ranchería and that extended varying distances down major Falls Creeks to carve out Hetch Hetchy Valley (the valley lies beneath the ice from about 6,200- drainages (see Alpha and others, 1987, for the to 7,000-ft ice-surface elevation). Earlier glaciers had only moderately higher surface elevations maximum extent of glaciers in the Tuolumne than those of the Tioga glaciation. From Alpha and others (1987). drainage during the Tioga glaciation). Because of this, the modern longitudinal profile of the Tuolumne River east of its Grand Canyon is almost wholly the result of glacial erosion, by the Tuolumne River at Tuolumne Meadows Only at Rancheria Mountain, however, can we whereas the profile through the Grand Canyon "about one-half to one-quarter million years estimate total postvolcanic incision rather than west to the glacial limit is the result of preglacial ago." If the conclusions that I reached above are simply incision below the prevolcanic channel. stream incision with glacial modification. correct, then there never was a trans-Sierra The volcanic deposits must thin westward, how- The Dana Fork of the Tuolumne has a rela- drainage through Tioga Pass, and 10 m.y. ago ever, and at some point, their upper surface tively uniform gradient from just west of Dana the Tuolumne River was already draining the would merge with the prevolcanic channel, and Meadows to just west of Tuolumne Meadows, Mount Dana area. total postvolcanic incision would be equal to and the smoothness of its profile is probably due The discussion presented above considers incision below the prevolcanic channel. to its glacial origin. It might be argued that the evidence for uplift after 10 m.y. ago—the only The modern Tuolumne River is not a graded very low gradient on the Lyell Fork for nearly datum available. At that time, however, the stream, as shown by its longitudinal profile 13 km above Tuolumne Meadows is due to its ancestral channel of the Tuolumne River at (Figs. 4, 8). East of Hetch Hetchy, the river is north-northwest azimuth normal to the regional Rancheria Mountain was moderately incised deeply incised eastward through the Grand slope, a direction that would be least affected by into a broader valley (Fig. 7). The presence of Canyon of the Tuolumne to about 6.5 km east uplift and tilt of the range. This is belied by the this incised channel suggests that the Tuolumne of Rancheria Mountain, at which point the abrupt climb to Mount Lyell, about 1,220 m, in basin was undergoing uplift before the lahar in- profile ascends over a series of cascades and re- about 6 km. I conclude that the profile is the filling about 10 m.y. ago. This idea is compatible turns to a lower gradient through Tuolumne result of scouring by massive Lyell Fork glaciers with evidence from the San Joaquin study Meadows (Fig. 8). Post-uplift incision of the throughout the Pleistocene. Glacial ice flowing (Huber, 1981) for earlier uplift, but the timing Tuolumne alone could not produce such an through Tuolumne Meadows was about 610 m and amount for the Tuolumne system still re- anomalous profile. thick and 10 km wide at the Lyell-Dana Forks main unknown. During the preglacial evolution of the Tuo- junction (Alpha and others, 1987). The step on lumne River, the most abrupt and significant the Dana Fork just east of this junction (Fig. 8) LATE CENOZOIC STREAM INCISION change in local base level occurred at Rancheria reflects a hanging-valley effect where the Dana Mountain 10 m.y. ago when 610 m of lahar Fork glacier joined the larger and deeper Lyell The reconstructed stream profile for the an- deposits filled the old channel. From the south Fork glacier. Below Tuolumne Meadows, gla- cestral Tuolumne River used in the uplift calcu- end of the volcanic dam near Rancheria Moun- cial ice became confined within the inner gorge lations can also be used to estimate the amount tain to the terminus of the lahar more than 65 of the Tuolumne (Fig. 10), and glacial plucking of stream incision during the past 10 m.y. At the km to the west, the gradient of the new channel is probably the cause of some of the irregularities easternmost exposure of Tertiary gravel on Ran- of the Tuolumne would have been greatly in- in the profile there. The Cathedral Peak Grano- cheria Mountain (Figs. 3, 7), the stream gravel creased, perhaps as much as 8 m/km (Fig. 9). diorite, which underlies Tuolumne Meadows and adjacent valley slopes are overlain by nearly This increase would result in local, rapid chan- (Bateman and others, 1983), has large areas of 610 m (2,000 ft) of lahar and Table Mountain nel incision. Upstream from the knickpoint at widely spaced jointing, as evidenced by the Latite. After diversion, the stream probably the dam, however, in the area ponded behind prevalence of massive domes in the Tuolumne began cutting its new channel some 610 m the dam, channel incision would cease until the Meadows area. Glacial plucking, controlled by above the bottom of the older one. The present knickpoint migrated up through this area to variations in joint spacing, including areas of channel is about 915 m (3,000 ft) lower than the coincide with the older channel. Above the more closely spaced joints downstream from older one (Fig. 7), and so total incision at ponded area, the lahar dam had no immediate Tuolumne Meadows, probably helped create the Rancheria Mountain during the past 10 m.y. effect on incision. Because the 10-m.y.-old cascades and other irregularities in the stream was about 1,525 m (5,000 ft). If the previous stream profile is poorly delimited east of Ran- profile there. uplift calculations are approximately correct, cheria Mountain, it is difficult to estimate the Some deepening of the Grand Canyon of the post-10-m.y.-ago uplift at Rancheria Mountain extent of the ponding, but it could easily have Tuolumne undoubtedly resulted from glacial would be about 1,097 m (3,600 ft), placing the reached the Tuolumne Meadows area. The steep erosion. Tributaries such as Piute Creek (Fig. 8) present channel about 183 m (600 ft) higher in reach of the present Tuolumne River may reflect descend rather steeply into the canyon and may, elevation than the older one was before uplift. the volcanically created knickpoint, which has in part, reflect glacial deepening of the canyon. Isolated exposures of lahar permit reconstruc- migrated upstream from Rancheria Mountain Local widening also occurred, as in Pate Valley tion of the lO-m.y.-old Tuolumne channel with since about 10 m.y. ago. at the junction with Piute Creek, but most of the some degree of confidence, from Rancheria The central Sierra Nevada was probably ex- Grand Canyon has a surprisingly V-shaped cross Mountain westward for about 53 km (Fig. 4). tensively glaciated many times during the Pleis- section for a valley that contained a glacier

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Dana Meadows - Drainage divide west of Tuolumne Tuolumne Meadows -i Meadows 10000 10000 Pywiack Cascade —

8000 Nevada Fall -, . Probable limit of 8000 ti maximum glaciation Vernal Fall LU Limit of Tioga 6000 glaciation ^ — — 6000 z o ""Yosemite Valley 5 4000 s

2000 Hetch Hetchy 2000 Valley of - Tuolumne profile Sea Sea Level Level 10 KILOMETERS

VERTICAL EXAGGERATION 5.2x

Figure 11. Longitudinal profiles of Merced River and tributary Tenaya Creek, with Tuolumne River for comparison. All profiles follow stream courses but ignore minor meanders. The Tuolumne plot is superimposed to intersect at the 4,000-ft elevation, the elevation of the Merced-Tenaya junction at the head of Yosemite Valley. The dotted line indicates the bedrock basin in Yosemite Valley, as interpreted from seismic data (Gutenberg and others, 1956). The dashed line indicates the inferred average trend of the pre-glacial Merced River without the Yosemite Valley basin, although some excavation below the line probably resulted from stream erosion prior to glaciation.

nearly 1,220 m thick. Possibly the canyon had a During each major glaciation, including the pects. First, the head of the Middle Fork of the deeply incised V shape prior to glaciation and Tioga, which probably peaked only about San Joaquin River was east of the present Sier- sheet joints parallel to the walls controlled gla- 15,000-20,000 yr ago, the Tuolumne canyon ran drainage divide at the site of Deadman Pass cial plucking and the tendency for valley widen- was filled to the brim with ice at least as far west (Figs. 1,2) until about 3.2 m.y. ago and drained ing (Clyde Wahrhaftig, 1988, oral commun.). as Mather, some 10 km beyond Hetch Hetchy a much larger area than it does today. I find no Obviously, this section of the canyon resisted (Fig. 10). Thus, Hetch Hetchy has been glacially evidence that the Dana Fork of the Tuolumne conversion to a U-shape. Finally, Hetch Hetchy scoured "recently." Yosemite Valley, however, River ever headed east of the range, crossing in Valley occurs on the Tuolumne below the junc- has not been filled with ice for at least 750,000 the vicinity of the present Tioga Pass, even be- tions of three major tributary glaciers entering yr, the minimum age of the Sherwin glaciation, fore the late Cenozoic uplift of the range. Thus, from the northeast; perhaps a glacially excavated which is probably equivalent to Matthes' El Por- the area of the Tuolumne drainage basin has bedrock basin lies concealed beneath alluvium tal glaciation in Yosemite (Huber, 1987). Thus, remained nearly constant for a much longer pe- in the valley upstream from the narrows at the the major excavation of Yosemite Valley, in- riod of time than has that of the San Joaquin. foot of the valley, as in Yosemite Valley (Guten- cluding the bedrock basin beneath the valley Second, the San Joaquin River flowed virtually berg and others, 1956). floor, had to have been accomplished by that uninterrupted in its present channel, probably time, and since then, freeze-thaw cycles have since the Eocene. In contrast, at least 65 km of COMPARISON WITH THE MERCED promoted spalling of rock slabs, steepening the the Tuolumne channel was buried beneath as RIVER AND YOSEMITE VALLEY cliffs, and forming the recessed alcoves into much as 610 m of lahar and lava flows, and the which waterfalls such as Bridalveil now leap. river was forced to shift laterally and cut a new The longitudinal profiles of the Merced and For this reason, Hetch Hetchy Valley is in many channel into granitic bedrock about 10 m.y. ago. Tuolumne Rivers (Fig. 11) suggest that the Tuo- ways a "fresher looking" glaciated valley than Headward channel incision has not yet reached lumne River through Hetch Hetchy Valley was Yosemite Valley, long considered a classic gla- Tuolumne Meadows. close to its present profile before glaciation, and cially carved valley. Both studies provide evidence that late Ceno- that Yosemite Valley is almost entirely the result zoic uplift of the central Sierra Nevada was of glaciation. As a result, Yosemite is close to the CONCLUSIONS underway before 10 m.y. ago. This is compati- large abrupt steps at Vernal and Nevada Falls on ble with the concept that uplift resulted from the the Merced River and Pywiack Cascade on trib- The present study of the late Cenozoic evolu- evolution of the modern plate boundary along utary Tenaya Creek, whereas upstream from tion of the Tuolumne River reinforces many of California, beginning about 30 m.y. ago, from a Hetch Hetchy Valley, the Tuolumne rises more the conclusions reached in the earlier San Joa- subduction to a predominantly transform gradually over a longer distance through the quin study (Huber, 1981), although the geologic boundary. Concurrent with this change, region- Grand Canyon of the Tuolumne before climbing history of the Tuolumne drainage differs from al-scale extension began in the Basin and Range steeply to Tuolumne Meadows. that of the San Joaquin in two important as- province (Zoback and others, 1981).

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Dalrymple, G. B., 1963, Potassium-argon ages of some Cenozoic volcanic rocks Lindgren, Waldemar, 1911, The Tertiary gravels of the Sierra Nevada of Cali- ACKNOWLEDGMENTS of the Sierra Nevada, California: Geological Society of America Bul- fornia: U.S. Geological Survey Professional Paper 73,226 p. letin, v. 74, p. 379-390. Moore, J. G., and Dodge, F.C.W., 1980, Late Cenozoic volcanic rocks of the 1964, Cenozoic chronology of the Sierra Nevada, California: California southern Sierra Nevada, California: 1. Geology and petrology: Sum- This study benefitted greatly from many dis- University Publications in Geological Sciences, v. 47,41 p. mary: Geological Society of America Bulletin, Part I, v. 91, p. 515-518. cussions with my colleagues, especially Malcolm Dodge, F.C.W., and Calk, L. C., 1987, Geologic map of the Lake Eleanor Morton, J. L., Silberman, M. L., Bonham, H. F., Garside, L. J., and Noble, quadrangle, Central Sierra Nevada, California: U.S. Geological Survey D. C., 1977, K-Ar ages of volcanic rocks, plutonic rocks, and ore M. Clark, Franklin C.W. Dodge, George I. Geologic Quadrangle Map GQ-1639, scale 1:62,500. deposits in Nevada and eastern California—Determinations run under Dodge, F.C.W., and Moore, J. G., 1981, Late Cenozoic volcanic rocks of the the USGS-NBMG cooperative program: Isochron/West, no. 20, Smith, Clyde Wahrhaftig, and James C. Yount, southern Sierra Nevada, California; II. Geochemistry: Geological So- p. 19-29. and a very helpful review by Deborah R. ciety of America Bulletin, Pan H, v. 92, p. 1670-1761. Noble, D. C., Slemmons, D. B., Korringa, M. K., Dickinson, W. R„ Al-Rawi, Durrell, Cordell, 1966, Tertiary and Quaternary geology of the northern Sierra Yehya, and McKee, E. H., 1974, Eureka Valley Tuff, east-central Cali- Harden; they have my thanks. Thanks are also Nevada, in Bailey, E, H., ed., Geology of northern California: California fornia and adjacent Nevada: Geology, v. 2, p. 139-142. Division of Mines and Geology Bulletin 190, p. 185-197. Ransome, F. L., 1898, Some lava flows of the western slope of the Sierra due James Snyder, National Park Service, for Gibbons, A. B., Megeath, J. D., and Pierce, K. L., 1984, Probability of moraine Nevada, California: U.S. Geological Survey Bulletin 89, 71 p. logistic support that made possible my visit to survival in a succession of glacial advances: Geology, v. 12, p. 327-330. Schaffer, J. P., 1986, A geologic history of Yosemite Valley, in Topographic Gutenberg, Beno, Buwalda, J. P., and Sharp, R. P., 1956, Seismic explorations map of Yosemite Valley: Berkeley, California, Wilderness Press, scale Ranchería Mountain. on the floor of Yosemite Valley, California: Geological Society of 1:24,000. America Bulletin, v. 67, no. 8, p. 1051-1078. Slemmons, D. B., 1966, Cenozoic volcanism of the central Sierra Nevada, Huber, N. K., 1981, Amount and timing of late Cenozoic uplift and tilt of the California, in Bailey, E. 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M., 1976, Evidence for rapid destruction of latest Pleistocene glaciers 1974, Hetch Hetchy Reservoir quadrangle, Yosemite National Park, MANUSCRIPT RECEIVED BY THE SOCIETY JANUARY 30,1989 of the Sierra Nevada, California: Geological Society of America Ab- California—Analytic data: U.S. Geological Survey Professional Paper REVISED MANUSCRIPT RECEIVED MAV 31,1989 stracts with Programs, v. 8, p. 361-362. 774-B, 15 p. MANUSCRIPT ACCEPTED JULY 12,1989

Printed in U.S.A.

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