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Amount and timing of late Cenozoic uplift and tilt of the central Sierra Nevada, California: Evidence from the upper San Joaquin River basin

1981; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp1197

2330-7102

N. King Huber,

Seismic Waves and Analysis

The upper San Joaquin River is unique among the rivers that drain the western slope of the Sierra Nevada in that it flowed westward across the present crest of the range until as recently as about 3.2 mill ion years ago.Portions of the history of the river and of the topog raphic development of the central Sierra Nevada can be deciphered from tilted stratigraphic planes at the east margin of the Central Val ley and dated volcanic rocks within and east of the upper San Joa quin River's present drainage basin.Uplift of the central Sierra Nevada was probably underway by 25 m.y.ago, but at a relatively low rate, probably not exceeding about 0.03 mm/yr at the present drainage divide at Deadman Pass.Uplift proceeded at an increasing rate, and is an estimated 0.3 mm/yr at present; the rate may still be increasing.Total uplift at Deadman Pass in the past 50 m.y. is esti mated to be about 3450 m, of which two-thirds took place in the last 10 m.y. and one-fourth in the last 3 m.y.Of these estimates, the amounts of pre-10 m.y.uplift and post-3 m.y.uplift are the most speculative.Highlights of the uplift history, ignoring qualifications discussed in the text, include: 1.During deposition of the Eocene lone Formation in the Central Val ley, perhaps 50 m.y.ago, the San Joaquin River drained a sig nificant area to the east of the range.Because major peaks on either side of the San Joaquin canyon presently rise only 450-750 m above the projected Eocene local base level, relief in the area was comparatively low.2. Between 50 and 10 m.y.ago, uplift of about 1300 m occurred at the site of Deadman Pass on the present Sierran drainage divide.Major peaks stand 1500 to 1700 m above the 10-m.y.local base level, indicating that relief had increased.The stream profile at the site of Deadman Pass was about 900 m above sea level 10 m.y.ago.3.After it began, uplift and westward tilt of the range accelerated; by somewhat more than 3 m.y.ago, the site of Deadman Pass had been uplifted an additional 1200 m, and incision of the inner canyon of the San Joaquin River in response to uplift was well advanced.4.About 3.2 m.y.ago, the San Joaquin River was beheaded by the eruption of basalt that filled the channel near Deadman Pass.Water previously flowing in this channel was probably diverted into the already-forming Owens Valley graben.5.An additional 950 m of uplift at Deadman Pass took place after about 3 m.y.ago, for a total of 2150 m since about 10 m.y.ago.Until about 3 m.y.ago, the area east of Deadman Pass probably rose along with the Sierran block, but then lagged behind it, re sulting in relative downward displacement along faults east of Deadman Pass of about 1100 m. 6. Partial infilling of the inner canyon by basalt and the greatly re duced stream discharge, particularly in the Middle Fork, which had been the main trunk of the river, greatly reduced rates of canyon downcutting by stream erosion in the last 3 m.y.Glacial erosion consequently was the dominant mechanism for removal of the basalt, additional incision into prevolcanic bedrock, and enhancement of the concavity of the longitudinal stream profile upstream from Mammoth Pool Dam. 7. The elevation of the Sierra Nevada 3 m.y.ago may not have been high enough to permit extensive glaciation at that time.The lag deposit at Deadman Pass, previously described as a till, may be of nonglacial origin.123°122°121°120°119°118°3 9°3 8°3 7°3 6° -FIGURE 1.-Generalized topographic contour map of central California.Contour interval 2000 ft (610 m); 1000-ft (305 m) contour is supplementary.From Christensen (1966)."Upper" San Joaquin River is that part east of Central Valley.