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Map Satellite Along the 700-meter (2,300-foot) long and up to 25-meter (80-foot) deep roadcut there is an excellent display of the shallow subsurface rocks lying within this segment of the San Andreas Fault Zone. The fault itself, which shifts position in time and which is usually defined as the trace of the most recent surface rupture, passes beneath the freeway at the southern end of the cut. Here there is a gouge zone 15 meters (50 feet) wide. The exposure, which exhibits severe and complex folding, is primarily of the mid-Pliocene Anaverde Formation, with some Pleistocene fanglomerate sediments at the southern end. The Anaverde Formation is found in the region only between the San Andreas and Little Rock Faults, the latter lying some 120 meters (400 feet) north of the cut. Nonmarine arkose sandstone and gypsiferous shale, the latter containing between 80 percent and 90 percent gypsum in some places, are the primary components of the Formation. The area may be divided into three zones, separated by older faults; the southern consisting primarily of arkosic sandstone, the middle, shale bed with some arkose, and the northern, alternating gypsiferous shale and arkose. The arkose in the middle section does not match that in the others, suggesting a lateral displacement along the bounding faults. Integrity: The cut, made in the early seventies, is subject to weathering of the shale and the leaching of the gypsum. Use: Educational, research, observational. Its location along a major freeway makes access and study hazardous. Ref: Smith, Drew, P., 1976. Roadcut Geology in the San Andreas Fault Zone. Calif. Gap. 29 (5), pp. 99 - 104. December 1979
Inventory of California Natural Areas
Revision © 2008 Steven Louis Hartman
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