GEOLOGIC MAPPING IN SAN LUIS OBISPO COUNTY ON THE CENTRAL COAST OF CALIFORNIA

The California Geological Survey (CGS) is engaged in a multi-year project to prepare a seamless onshore/offshore geologic map and geologic database of theof the western half of the San Luis Obispo 30’ x 60’ quadrangle in the Central Coast region of California. So far, eight 7.5’ quadrangle geologic maps have been completed (Morro Bay South, San Luis Obispo, Pismo Beach, Atascadero, Arroyo Grande NE, Oceano, Nipomo and Santa Margarita). Two quadrangles are in preparation and will be released in June, 2016 (Morro Bay North and Cayucos). Work on the finalized onshore/offshore database will commence in the second half of 2016. This project is funded in part by the STATEMAP component of the National Cooperative Geologic Mapping Program.

Coastal San Luis Obispo County is a region of active crustal deformation and high seismicity caused by transpressive movement between the Pacific and North America Plate. Deformation is accommodated by slip along a number of active and potentially active faults that extend through the area, including the Rinconada, Oceano, Los Osos, West Huasna Faults and the Southwest Boundary Fault Zone of the San Luis Range. The active Hosgri and Shoreline Faults lie just offshore.

In addition to CGS’s mapping activities, western San Luis Obispo County has been the focus of extensive seismic hazard studies by Pacific Gas & Electric (PG&E) and their team of prominent geologic and seismologic consultants to apply for a twenty year renewal of their license to operate Diablo Canyon Power Plant, a nuclear facility about 8 miles southwest of San Luis Obispo. Following detailed guidelines developed by the Nuclear Regulatory Agency, extensive new onshore and offshore data are being generated by PG&Es geosciences staff and their consultants in collaboration with the USGS California Seafloor Mapping Program and the California State University Seafloor Mapping Lab. These data will be included in the geologic map database as it becomes available.