Preliminary soil-slip susceptibility maps, southwestern California

This data set maps the soil-slip susceptibility for several
areas in southwestern California. Created using Environmental
Systems Research Institute's ARC/INFO software, the data base
consists of raster maps containing grid cells coded with soil-
slip susceptibility values. In addition, the data set includes
the following graphic and text products: (1) postscript graphic
plot files containing the soil-slip susceptibility map,
topography, cultural data, and a key of the colored map units,
and (2) PDF and text files of the Readme (including the
metadata file as an appendix) and accompanying text, and a PDF
file of the plot files.
Intense winter rains commonly generated debris flows in upland
areas of southwestern California. These debris flows initiate
as small landslides referred to as soil slips. Most of the
soil slips mobilize into debris flows that travel down slope
at varying speeds and distances. The debris flows can be a
serious hazard to people and structures in their paths. The
soil-slip susceptibility maps identify those natural slopes
most likely to be the sites of soil slips during periods of
intense winter rainfall. The maps were largely derived by
extrapolation of debris-flow inventory data collected from
selected areas of southwestern California. Based on spatial
analyses of soil slips, three factors in addition to rainfall,
were found to be most important in the origin of soil slips.
These factors are geology, slope, and aspect. Geology, by far
the most important factor, was derived from existing geologic
maps. Slope and aspect data were obtained from 10-meter
digital elevation models (DEM). Soil-slip susceptibility maps
at a scale of 1:24,000 were derived from combining numerical
values for geology, slope, and aspect on a 10-meter cell size
for 128 7.5' quadrangles and assembled on 1:100,000-scale
topographic maps. The resultant maps of relative soil-slip
susceptibility represent the best estimate generated from
available debris-flow inventory maps and DEM data.