San Francisco Bay Region landslide folio part E - Map of debris-flow source areas in the San Francisco Bay region, California

This map identifies the principal areas in the San Francisco Bay
region that are likely to produce debris flows, which are also
called "mudslides." Debris flows that occur in the bay region are
fast-moving downslope flows of mud that may include rocks,
vegetation, and other debris. These flows begin during intense
rainfall as shallow landslides on steep slopes. The rapid movement
and sudden arrival of debris flows pose a hazard to life and
property during and immediately following the triggering rainfall.
Debris flows in a given storm originate from a number of sources
scattered throughout steep parts of the landscape, as shown in
figure 1 (on map sheet; files sfbr- df.ps, al-df.ps, etc.). During
subsequent storms, new debris flows originate from different
sources. These various sources, however, are similar in topographic
form because debris-flow initiation requires steep slopes and
prefers concave parts of hillsides.