Geology of the upper Tick Canyon area, Los Angeles County, California

Abstract

The upper Tick Canyon area, approximately seven square miles in extent, lies between Agua Dulce Canyon and Mint Canyon in the easternmost pelt of the Ventura Basin in southern California. This area was mapped in detail on a scale of 1000 feet to one inch and the stratigrephic and structural relationships of the exposed rocks were established. The oldest rocks in the area are of highly metamorphosed metasedimentary and metavolcanic types, which are intruded by igneous bodies of presumed pre-Cretaceous age. This crystalline complex is in fault contact with the rocks of the Vasquez series, the oldest unit in a thick section of Tertiary sedimentary and volcanic rocks. The Vasquez series is perhaps Oligocene in age and was deposited under nonmarine conditions in an elongate trough of fault-block origin. The rocks are mainly fine-to coarse- grained elastic sediments. Interlayered with them are basaltic and andesitic flows and shallow intrusive masses, that form with the sediments a total section of about 4500 feet. This section thickens rapidly east of the area mapped. Overlying the Vasquez strata with a distinct angular unconformity is a series of conglomerates and siltstones of the late Lower Miocene Tick Canyon formation. This unit is approximately 900 feet thick, but thins rapidly to the west within the area under consideration. The Upper Miocene Mint Canyon formation, which also consists of nonmarine elastic sedimentary rocks overlies the Tick Canyon formation throughout the area. These two formations probably are separated by an unconformity, along which there may be local angular discordance of a few degrees. Almost flat-lying, Pleistocene stream deposits occur throughout the area at an elevation of several hundred feet above the present, newly alluviated valley bottoms. Some strike-slip faulting with northeasterly trend took place after Mint Canyon time, perhaps during the Pliocene epoch. This may be related to the San Andreas fault, which lies ten miles to the northeast. All folds and faults that involve the sedimentary beds probably can be related to adjustments taking place in the underlying crystalline rocks. The forces causing these adjustments probably were active throughout much of Tertiary and Quaternary time, and activities do not appear to have ceased as yet.