Page 13 - stitt1981

GEOLOGY OF THE VENTURA AND SOLEDAD BASINS IN THE
VICINITY OF CASTAIC, LOS ANGELES
COUNTY, CALIFORNIA

INTRODUC TION

Regional Setting

The Castaic study area is located approximately 40 miles (65 kin)

northwest of downtown Los Angeles, and covers approximately 70

square miles (190 kin2) within the Newhall, Val Verde, Whitaker Peak,

and Warm Springs Mountain 7.5 minute topographic quadrangles of the

U.S. Geological Survey.

The area is located in that part of the central Transverse Ranges

of California where the Ridge, Soledad, and Ventura basins adjoin one

another (Figure 1). The San Gabriel fault transects the area from

northwest to southeast and marks the boundary between the Ventura

basin to the west and the Ridge and Soledad basins to the east. Neo-

gene sedimentary rocks of the Ventura basin are primarily of marine

origin, whereas those of the Ridge and Soledad basins are primarily

nonmar me.

In the Castaic area, the San Gabriel fault separates two distinct

stratigraphic sections of Miocene and older rocks (Plate I; Figure 2).

Marine rocks of the Pliocene Pico Formation of the Ventura basin

correlate across the San Gabriel fault with minor strike-slip offset,