Topography, the configuration of the land surface, plays a major role in various natural processes
that have helped shape the ten-county San Francisco Bay region and continue to affect its
development. Such processes include a dangerous type of landslide, the debris flow (Ellen and
others, 1997) as well as other modes of slope failure that damage property but rarely threaten life
directly?slumping, translational sliding, and earthflow (Wentworth and others, 1997). Different
types of topographic information at both local and regional scales are helpful in assessing the
likelihood of slope failure and the mapping the extent of its past activity, as well as addressing
other issues in hazard mitigation and land-use policy. The most useful information is quantitative.
This report provides detailed digital data and plottable map files that depict in detail the most
important single measure of ground-surface form for the Bay region, slope angle. We computed
slope data for the entire region and each of its constituent counties from a new set of 35,000,000
digital elevations assembled from 200 local contour maps.