Photograph of Tower Peak taken in 2005 by Ed Farrell
Clyde Wahrhaftig mapped the geology of the Tower Peak quadrangle in great detail at a scale of 1:24,000 between 1955 and 1980. For use in preparing a geologic map of Yosemite National Park (Huber and others, 1989), Wahrhaftig reduced and generalized his geologic map to a scale of 1:48,000. Clyde died before he could complete a 1:62,500 scale version to match other published 15-minute geologic quadrangles of the park. Consequently, the present version was compiled by N. King Huber from materials left by Clyde and from geologic information from adjacent quadrangles. It is hoped that the resulting map does not seriously compromise Clyde's interpretations. Publication of the map was supported by a contribution from the Clyde Wahrhaftig Trust.
The Tower Peak quadrangle, which includes northernmost Yosemite National Park, is located astride the glaciated crest of the central Sierra Nevada and covers an exceptionally well-exposed part of the Sierra Nevada batholith. Granitic plutonic rocks of the batholith dominate the geology of the Tower Peak quadrangle, and at least 18 separate pre-Tertiary intrusive events have been identified. Pre-Cretaceous metamorphic rocks crop out in the quadrangle in isolated roof pendants and septa. Tertiary volcanic rocks cover granitic rocks in the northern part of the quadrangle, but are not considered in this brief summary.
Potassium-argon (K-Ar) age determinations for plutonic rocks in the quadrangle range from 83 to 96 million years (Ma), including one of 86 Ma for the granodiorite of Lake Harriet (Robinson and Kistler, 1986). However, a rubidium-strontium whole-rock isochron age of 129 Ma has been obtained for the Lake Harriet pluton (Robinson and Kistler, 1986), which field evidence indicates is the oldest plutonic body within the quadrangle. This suggests that some of the K-Ar ages record an episode of resetting during later thermal events and are too young. The evidence indicates that all the plutonic rocks are of Cretaceous age, with the youngest being the Cathedral Peak Granodiorite at about 83 Ma.
The pre-Tertiary rocks of the Tower Peak quadrangle fall into two groups: (1) an L-shaped area of older plutonic and metamorphic rocks, 3 to 10 km wide, that extends diagonally both northeast and southeast from near the center of the quadrangle; and (2) a younger group of large, probably composite intrusions that cover large areas in adjacent quadrangles and extend into the Tower Peak quadrangle from the east, north, and southwest.
Download i2697.pdf a PDF file of the map (~38" x 24"; 7.5 MB)
Download i2697.ps an EPS version of the map for plotting (31 MB)
For questions about this report, contact Jim Moore (USGS) or Greg Stock (Yosemite National Park)
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This map is also available in printed form by writing:
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URL of this page is: http://pubs.usgs.gov/imap/i2697/
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Michael Diggles
Created: October 4, 2000 (cad)
Updated: December 18, 2008
(bwr, mfd)
