Geology of the Central Portion of the Mount Pinos Quadrangle, Ventura and Kern Counties, Southern California

Abstract

The central portion of the Mount Pinos quadrangle lies principally in northern Ventura County and includes a small district in the adjacent part of Kern County. The rocks within the area mapped are of pre-Cretaceous, Cretaceous (?), Eocene, Miocence, and Quarternary ages. The oldest rocks consist of metamorphosed sediments, prinicipally calcareous; quartz, diorite porphyry; and granitic gneiss and schist. The Cretaceous (?) and Eocene have not been differentiated and only the latter has been definitely recognized; the combined thickness exposed approaches 15,000 feet. The Miocene rocks are predominantly marine west of the Cuyama River, but to the east a very thick section of terrestial deposits has accumulated, extending into Lockwood Basin, and perhaps farther. These strata are strikingly colored and give rise to an extensive area of badlands. The structure of the western part of the area is characterized by numerous folds and occasional faults; both have roughly a N.W.W. trend. In the eastern portion or Lockwood Basin the deformation is more acute and faulting has played a larger part. The majority of the structural features in this eastern region strike northeasterly and are of a compressional nature, although normal faulting also occurs. Transverse to the prevalent strike in Lockwood Valley, and at least in part of later origin, is a group of faults which have had dominantly horizontal movement. The San Andreas Rift, extending across the northeastern corner of the area, is the major feature in the latter group. From an economic standpoint this area is of historic interest, as one of the early discoveries of gold in California was made in or near San Guillermo Creek, and the colemanite deposits in Lockwood Valley played an important part in the early borax mining of the State.