NEW DIGITAL GEOLOGIC MAP DATABASE AND STRATIGRAPHIC FRAMEWORK; UNDERPINNINGS FOR 3D GEOLOGIC MAPPING AND STRUCTURAL ANALYSES IN THE CENTRAL CALIFORNIA COAST RANGES

We are compiling an improved and expanded digital geologic map database for the central California Coast Ranges in support of tectonic analyses and as a primary data source for a 3D geologic map. The area of interest consists of approximately 23,000 square kilometers between Monterey Bay to the north and the Santa Ynez Mountains to the south, between the Pacific Ocean to the west and the San Andreas Fault to the east. This region forms an important tectonic link between the relatively well-studied fault systems of the San Francisco Bay region and the Los Angeles region. Our basic approach is digital compilation of existing "paper" geologic maps, building on existing compilations for Monterey and San Luis Obispo counties and the Santa Maria 30' x 60' quadrangle, to produce the requisite GIS layers for related tectonic studies. However, geologic mapping in this region is characterized by a generalized stratigraphic nomenclature, so that geologic units of disparate age and(or) depositional environment have been given the same name. For example, the base of the Monterey Formation as presently mapped varies from early Miocene to late Miocene. If used for tectonic analyses the present nomenclature will introduce significant errors, because geologic units of the same name are assumed to be correlative. Therefore we are revising the stratigraphic framework so that distinctions in age and(or) depositional environment are reflected in the geologic map database. We are also developing a series of geologic map based cross-sections in order to constrain structural orientation and style. The geologic map data are being combined with other datasets (potential field geophysics, well data, seismic data) to produce a 3D geologic map of the region along with a kinematic analysis of the active fault system in and bounding the region.