g and sliding may occur simultaneously. In addition, mass movements often follow a sequence: falling, sliding, and flowing (Campbell et al. 1-27).
In southern California mass earth movement is a common. It results from the simultaneous occurrence of unstable slopes, fractured substrate, a mediterranean climate, and chronic vegetal disturbances (e.g., fire) (Minnich 91-100). Typical landslides span the range from "sudden and catastrophic" to "slow and insidious." In the winter of 1969, for example, two intense southern California rainstorms caused 10 slip-debris flow events on chaparral-, sagebrush-, and grass-covered slopes. The different incidents resulted in a total of 20 fatalities. Then, in 1978, another two rainstorms again triggered major debris flows and extensive flooding. In that particular year, storm-triggered landslide damage cost the City of Los Angeles $50 million. Two years later, in 1980, the city was hit once more. Over a period of 8 days, landslides and flooding resulting from a series of six major rainstorms cost the city $70 mi
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