This map identifies the principal areas in the San Francisco Bayregion that are likely to produce debris flows, which are alsocalled "mudslides." Debris flows that occur in the bay region arefast-moving downslope flows of mud that may include rocks,vegetation, and other debris. These flows begin during intenserainfall as shallow landslides on steep slopes. The rapid movementand sudden arrival of debris flows pose a hazard to life andproperty during and immediately following the triggering rainfall.Debris flows in a given storm originate from a number of sourcesscattered throughout steep parts of the landscape, as shown infigure 1 (on map sheet; files sfbr- df.ps, al-df.ps, etc.). Duringsubsequent storms, new debris flows originate from differentsources. These various sources, however, are similar in topographicform because debris-flow initiation requires steep slopes andprefers concave parts of hillsides.