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ABSTRACT

The Soledad basin is situated north of the San Gabriel

Mountains, in Los Angeles County, California, and its center is about

35 miles north of the Los Angeles civic center. Roughly an elongate

parallelogram in shape, this basin has dimensions of about ten by

thirty miles, with the longer dimension oriented east-west. The Sierra

Pelona and the San Gabriel Mountains form the northern and southern

boundaries, respectively. The San Andreas fault and the San Gabriel

fault, both of which trend northwest in this region, bound the basin on

its northeast and southwest borders, respectively. Only the northern

part of the basin is discussed in this paper.

The pre-Cretaceous Pelona schist, the oldest unit in the map

area, is a thick sequence of muscovite schist, chlorite-muscovite

schist and actinolite-chlorite schist with rare layers of quartzite and

limestone. This unit underlies the Sierra Pelona, an elongate mountain

mass which trends east-west. Granitic intrusive rocks of probable

late Jurassic age underlie a complex section of Tertiary rocks in mo st

of the eastern Soledad basin. Gneisses, some of which may represent

. highly injected Pelona schist, also are present in a belt that in general

trends parallel to the Sierra Pelona~

In general, the sedimentary beds exposed at the surface are

younger from east to west in the Soledad basin. The marine Martinez

formation of Paleocene age is the oldest sedimentary unit in the region.