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A continuously deposited, clastic sequence of Upper Cretaceous, lower and middle Eocene marine sedimentary rocks lies unconformably on granitic basement in the La Panza, southern Santa Lucia, and Sierra Madre Ranges of central California. The sequence is more than 30,000 ft thick and is bounded by the San Andreas and Nacimiento fault zones.
Sediment accumulated in a steep-sided, troughlike basin southwest of the present San Andreas fault zone. The basin extended southeastward across the Big Pine and Pine Mountain faults into the Ventura basin in which the lower Tertiary sequence of the Santa Ynez Mountains accumulated. The wedge-shaped area, including the San Rafael Mountains, between the Sierra Madre trough and the Ventura basin, underwent uplift and erosion during Late Cretaceous and early Eocene time. During the late early Eocene, a marine transgression resulted in deposition of a thin limestone, followed by shales and sandstones, across the southeastern part of the San Rafael wedge-shaped area.
The lower Tertiary strata of the Soledad area, north and east of Castaic and east of the San Gabriel fault, accumulated in the probable eastward extension of the Sierra Madre-Ventura composite basin. The composite basin may have extended as far south as the Channel Islands.
Paleocurrent and stratigraphic studies in the lower Tertiary sequence deposited in the Sierra Madre basin indicate deposition mainly from a source area on the east, as in the Ventura basin. A possible source area may be the basement rocks of the Mojave Desert, San Bernardino Mountains, and the Orocopia Mountains.
The Eocene of the Orocopias is a possible eastward extension of the composite basin that has been displaced along the San Andreas fault. The Poway "conglomerate suite" of Eocene sediments from southern California was probably deposited in a separate basin south of the Sierra Madre-Ventura composite basin.
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