Print this pageAbstract: Geologic Overview of Santa Rosa Island
WOOLLEY, JOHN J., Venoco, Inc., Santa Barbara, CA 93101
Santa Rosa Island, a unit of Channel Islands National Park, lies about 50 km SW of Santa Barbara, CA. Its 215 km2 area consists of Tertiary sedimentary and volcanic rocks.
The oldest rocks exposed are the middle Eocene South Point and Cozy Dell Formations, a deep-sea fan sand and basinal shale, respectively. Overlying these are a trangressional sequence consisting of the Oligocene Sespe redbeds, early Miocene Vaqueros shallow marine sandstone and siltstone, and the deeper water deposits of the middle Miocene Rincon and Monterey Formations.
Two formations unique to the northern Channel Islands are associated with the Monterey Formation; stratigraphic relationships are not clear. The San Miguel Volcanics consist of a series of marine volcaniclastics, basaltic flows and shallow intrusives. The Beechers Bay Formation is the youngest unit on the island. It is a submarine fan complex containing generally coarse- grained volcaniclastic sediments probably derived from a different volcanic center than those of the San Miguel Volcanics, along with metamorphic rocks including blueschist.
Quaternary processes are illustrated by features including large stabilized dune fields which maybe related to extinction of the pygmy mammoth about 12,000 years ago. A Recent and/or historic barranca and gully system was exacerbated by overgrazing by sheep in the 19th century, but its origins and chronology are poorly understood.
AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California