The map area encompasses a large part of the western Transverse Ranges
and southern Coast Ranges of southern California. The San Andreas fault
(SAF) cuts the northern part of the map. The area south of the SAF, about
80 percent of the map area, encompasses several distinct tectonic blocks
bounded by major thrust or reverse faults, including the Santa Ynez fault,
Big Pine fault (and structurally continuous Pine Mountain fault), Tule Creek
fault, Nacimiento fault, Ozena fault, Munson Creek fault, Morales fault,
and Frazier Mountain Thrust System. Movement on these faults is as old as
Miocene and some faults may still be active. In addition, the Paleocene
Sawmill Mountain Thrust south of the SAF and the Pastoria Thrust north of
the SAF place Cretaceous and older crystalline rocks above Pelona Schist
(south of the SAF) and Rand Schist (north of the SAF).
South of the SAF, each tectonic block contains a unique stratigraphy,
reflecting either large-scale movement on bounding faults or different
depositional environments within each block. On Mount Pinos and Frazier
Mountain, intrusive and metamorphic rocks as old as Mesoproterozoic, but
including voluminous Cretaceous granitoid rocks, underlie or are thrust
above non-marine sedimentary rocks as old as Miocene. Elsewhere, marine
and non-marine sedimentary rocks are as old as Cretaceous, dominated by
thick sequences of both Eocene and Cretaceous marine shales and sandstones.
Middle Miocene to early Oligocene volcanic rocks crop out in the Caliente
Hills (part of Caliente Formation) and south of Mount Pinos (part of the
Plush Ranch Formation). Fault-bounded windows of Jurassic Franciscan
Complex ophiolitic rocks are evident in the southwest corner of the area.
North of the SAF, marine and non-marine sedimentary rocks as old as
Eocene and Miocene volcanic rocks overlie a crystalline basement complex.
Basement rocks include Cretaceous intrusive rocks that range from
monzogranite to diorite, and Jurassic to late Paleozoic intrusive and
metamorphic rocks. The Jurassic to late Paleozoic intrusive rocks include
diorite, gabbro, and ultramafic rocks, and the metasedimentary rocks
include marble, quartzite, schist, and gneiss.