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Lowell Kessel, 1998




Project Title

Lowell Kessel
UC Santa Barbara Arthur Sylvester,
UC Santa Barbara
Folding and faulting along the San Andreas fault, Palmdale, California; Implications for simple shear mechanics and education of the public


The hwy 14 road cut in Palmdale, California, is the location of one of the best shallow subsurface exposures of the San Andreas fault zone and its related structures along its entire 1000 km length. The fault zone is 1.6 km (1 mi.) wide at Palmdale (Barrows, 1987) and consists of a set of faults that parallels the San Andreas fault (SAF). Approximately 3km to the east, the SAF zone, spans a width of 3.2 km (2 mi.) (Barrows, 1987) and commonly spans a width of several kilometers along its extent.

The Palmdale roadcut, about 27 m high and about 600 m long, exposes complexly folded and faulted, middle Pliocene, gypsiferous lacustrine rocks known as the Anaverde Formation (Wallace, 1949). The Mojave segment of the SAF, along which the most recent rupture in 1857 occurred, crosses the highway at the southern end of the roadcut. The roadcut is aligned nearly perpendicular to the strike of the fault and can be considered to be a large "trench." At the north end of the cut and parallel to the SAF is the Little Rock fault which has had more than 20 km (Barrows 1987) of right lateral strike slip. The Little Rock fault is not exposed but located about 76m (250 ft) north of the northern end of the road cut (Smith, 1976). The "trench" allows a close look at the shallow subsurface structure and deformation possibly related to these two strike-slip faults.

The San Andreas fault is one of the longest and best-known continental strike-slip faults in the world, and this segment of the SAF has caused two of the three largest earthquakes in California in historic time, one being the 1857 Fort Tejon earthquake. As a geologist in California, I am compelled to contribute to the knowledge and education of this major active fault. My objective is to depict the structure of the roadcut and interpret its development in terms of regional faulting and local strike-slip faulting. This may educate people on the processes of strike-slip faults and the dynamics of tectonic geology.

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