SEAMLESS ONSHORE-OFFSHORE GEOLOGIC MAPPING FOR THE CALIFORNIA SEAFLOOR AND COASTAL MAPPING PROGRAM

Detailed (i.e., 1:24,000) geologic mapping in coastal environments typically ends at the shoreline, with “out of sight, out of mind” offshore areas rendered a uniform flat blue. As a result, these geologic maps fail to inform many important issues that transcend the shoreline such as source-to-sink sediment distribution and transport, earthquake hazards (e.g., mapping of active faults and unstable slopes), characterization of coastal aquifers, and relationships between onshore and offshore resources and habitats. Intensifying pressures on coastal environments from growing populations, infrastructure development, and climate change make this traditional geologic mapping approach increasingly untenable. The California Seafloor and Coastal Mapping Program (CSCMP) addresses this problem by providing new methods and a model for developing seamless onshore-offshore geologic maps.

CSCMP’s goal is to develop comprehensive bathymetric, geologic, and habitat maps and data for State Waters (shoreline to 3 nm offshore). CSCMP data acquisition includes onshore lidar topography, offshore swath bathymetry, high-resolution seismic-reflection profiles (~ 1 km line spacing), and digital camera and video “groundtruth” imagery. We used these publicly available data to generate 25 map publications covering about a third of California’s mainland coast, focused in the Santa Barbara Channel and between Monterey and Point Arena. Each publication contains a digital data catalog and 9 to 12 map sheets, including an onshore-offshore geologic map (1:24,000) that is a collaboration between the U.S. Geological Survey (USGS) and the California Geological Survey (CGS). CGS is using new lidar data as well as ifSar and NAIP imagery to upgrade and (or) re-map coastal onland geology with a focus on defining and refining Quaternary geology. USGS is using swath bathymetry and backscatter, seafloor samples, groundtruth imagery, and seismic-reflection data to delineate offshore units. Seismic profiles allow offshore mapping of faults and folds, as well as sediment facies, distribution, and thickness. In shallow waters (0 to 10 m depth) where offshore swath bathymetric mapping is restricted, we use bathymetric lidar and aerial photographs to map the nearshore area (0 to 10 m water depth) and to link the offshore and onshore geology.