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Descriptions of Field Trip Stops 7, 8, and 9

By
Christine Carlson
Christine Carlson
U.S. Geological Survey
345 Middlefield Road Menlo Park, California 94025
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Published:
January 01, 1984

Abstract

The sedimentary serpentinites we will visit are exposed in the southeast plunging Wilbur Springs anticline, where they interfinger with lower Cretaceous turbidites of the Great Valley Sequence. The Wilbur Springs area (Fig. 65) lies astride this anticlinal structure on the western edge of the Sacramento Valley approximately 175 km north of San Francisco (Fig. 61). The area is named for a hot springs resort on Sulfur Creek, which is located upstream from the Lodoga Road connecting Bear Valley with Highway 20. Barren, block-strewn, grass-free slopes or dense brush characterize areas underlain by serpentinite. Outcrops are sparse, and mainly confined to road and stream cuts. However, even in areas of poor exposure, contacts are easily traced in soils and subcrop. Because of the serpentinite, the area is highly suceptible to landslides and soil creep which locally bury or displace contacts.

The main outcrops of sedimentary serpentinite occur near Sulphur and Bear Creeks, south of Wilbur Springs. Here, thick bedded to massive, crudely stratified, foliate serpentinite breccia is the dominant lithologic facies. A quarry on Highway 20 and adjacent roadcuts provide excellent exposures of foliate serpentinite breccia and its stratigraphic relation with Great Valley strata.

Turn out at the large vista point and walk back across the road to examine the sandstone-shale sequence and the foliate serpentinite breccia exposures in the quarry and in roadcuts at either side. Relocation of the highway and backfill of the original quarry cut has removed some of the section and considerably degraded what remains. Nevertheless, the relationships seen here, though now with some difficulty, are significant enough to justify a look.

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Contents

SEPM Field Trip Guide

1984 Midyear Meeting San Jose, California

Ralph E. Hunter
Ralph E. Hunter
U. S. Geological Survey
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H. Edward Clifton
H. Edward Clifton
U. S. Geological Survey
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N. Timothy Hall
N. Timothy Hall
Foothill College
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John L. Chin
John L. Chin
U. S. Geological Survey
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SEPM Society for Sedimentary Geology
Volume
3
ISBN electronic:
9781565762787
Publication date:
January 01, 1984

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