U.S. Geological Survey Geologic Investigations Series I–2697
Clyde Wahrhaftig mapped the geology of the Tower Peak quadrangle in great detail (scale 1: 24,000) over a period of man y years from 1955 to 1980. For use in preparing a geologic map of Yosemite National Park (Huber and others, 1989), he reduced and generalized his geology to a scale of 1: 48,000. Clyde died before he could complete a 1: 62,500 version to match other published 15-minute geologic quadrangles in 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 result does not seriously compromise Clyde’s interpretations. Publication of the map was supported by a contribution from the Clyde Wahrhaftig Trust.
[The following text is from a draft prepared by Wahrhaftig and all of the interpretations are his. It has been slightly rearranged and edited by N. King Huber.]
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 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.
Last modified March 22, 2012
First posted October 4, 2000
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Contact Information, Western Region Geology and Geophysics Science Center—Menlo Park
U.S. Geological Survey
345 Middlefield Road, MS-973
Menlo Park, CA 94025-3591
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Wahrhaftig, Clyde, 2000, Geologic map of the Tower Peak quadrangle, central Sierra Nevada, California: U.S. Geological Survey Geologic Investigations Series I–2697, scale 62,500, available at https://pubs.usgs.gov/imap/i2697/.