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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 66 (1982)

Issue: 10. (October)

First Page: 1684

Last Page: 1684

Title: Geology and Slope Stability of Point Delgata, California: ABSTRACT

Author(s): Steven G. Barlow, William C. Tracy

Article Type: Meeting abstract


Two bedrock complexes crop out at Point Delgata in northern California: a Franciscan melange complex composed of sedimentary rocks, pillow basalts, and glaucophane schist; and the Franciscan coastal belt complex composed mainly of interbedded shales and sandstones. Two Quaternary formations largely cover these bedrock complexes.

The major geologic structure is the northwest-trending San Andreas fault, which cuts Point Delgata and forms the contact between the two Franciscan bedrock complexes. This active fault has extensively deformed the Quaternary deposits. The Franciscan coastal complex has numerous folds with axes sub-parallel to the trace of the fault.

Over 50 recent slope failures have occurred within the mapped area. Rotational slumps and debris flows within soil horizons are most Previous HitcommonNext Hit. The predominantly sandy soils of the area were found to have an average Previous HitangleTop of internal friction of 31.4°, and cohesion strength of 7.0 kg/m2.

Under static condition, slopes greater than 40° are basically unstable, but, during a major earthquake, condition slopes greater than 20° would likely be unstable.

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Copyright 1997 American Association of Petroleum Geologists