RECENT GEOLOGIC MAPPING OF WESTERN VENTURA COUNTY, CALIFORNIA: STATEMAP PROJECT COMPLETES MAPPING OF COASTAL SOUTHERN CALIFORNIA

The California Geological Survey (CGS) is in the second year of a four year STATEMAP funded project to map the geology of eleven 7.5-minute quadrangles in western Ventura County, California. These quadrangles comprise the eastern half of the Santa Barbara 1:100,000-scale quadrangle. Upon completion and integration with four 7.5-minute quadrangles in the western half of the Santa Barbara quadrangle, currently being completed by the USGS, detailed geologic mapping of coastal southern California from Santa Barbara to the U.S.-Mexico border will be complete.

The area mapped to date includes the Pitas Point, Ventura, Oxnard, and Point Mugu 7.5-minute quadrangles that contain the tectonically active Ventura basin and Oxnard Plain. The Ventura basin is a thick section of predominantly Cenozoic strata, folded and faulted by reverse faults with evidence for Late Quaternary displacement. These faults include the northward dipping Red Mountain and Ventura faults, and the southward dipping Oak Ridge fault. The project area is dominated by incompetent Miocene, Pliocene, and Quaternary strata of mostly mudstone and shale that contain numerous landslides. The relatively high uplift rates in the region exacerbate the landslide potential. The Santa Monica Mountains bound the Ventura basin to the south and are primarily composed of Miocene sedimentary rocks in the project area. The Oxnard Plain and associated Quaternary deposits have been mapped in detail and chronicle the avulsion of the Santa Clara River throughout the Holocene.