SEAMLESS DIGITAL LANDSLIDE INVENTORY AND GEOLOGIC DATABASES OF THE SANTA MONICA MOUNTAINS, SOUTHERN CALIFORNIA

The California Geological Survey (CGS) has developed two separate seamless digital databases of landslide inventories (LSI) and geologic maps of the Santa Monica Mountains National Recreation Area (SAMO). This work was part of a cooperative effort with the National Park Service (NPS) to provide NPS with two of the essential datasets of geologic and hazards information to include in their Geologic Resources Inventory of SAMO.

SAMO is in the Transverse Ranges Province, a tectonically active area where uplift, folding and faulting have produced steep slopes composed of deformed and weakened rocks, resulting in the widespread occurrence of landslides. CGS prepared LSI maps of the area as part of the Seismic Hazards Zonation Program (SHZP) in 1996 to 2002. For the NPS SAMO LSI project, CGS completed the digital database of landslide attributes, reconciled landslide mapping across quadrangle boundaries, and reviewed the maps for completeness. The 14 individual 7.5’ LSI maps will be published online as part of the CGS LSIM Series.

The NPS SAMO geologic map project involved reconciling geologic contacts and stratigraphic nomenclature between the Los Angeles 30’x60’ quadrangle by Yerkes and Campbell (2005) and the Santa Barbara 30’x60’ quadrangle by Gutierrez et al. (2008) to the west. CGS worked with Russell Campbell (USGS – retired) to update bedrock mapping and reconcile map-boundary issues between the 30’x60’ quadrangles. Quaternary units in the area were updated with detailed mapping by CGS for SHZP. Landslides are not included in this database except where the landslide deposits obscure the underlying bedrock to the point where the underlying bedrock contacts cannot be inferred.

Development of the two SAMO databases represents a major step toward the CGS goal of completing a new seamless geologic map database covering the Los Angeles 30’x60’ quadrangle. Campbell is continuing to update maps of the 7.5’ quadrangles, which will be published online as CGS Preliminary Geologic Maps. The new compilation will substantially update the previous compilation of Yerkes and Campbell (2005) with new Quaternary mapping, more detailed mapping of crystalline units, and more consistent stratigraphic nomenclature within the quadrangle and with adjacent maps. CGS welcomes comments and additional data from the geologic community.