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and Associates made several corrections and supplied a few new references.

A total of 335 landslides that have caused damage to manmade structures and 659 parcels ofland that have been devalued because oflandslide damage from 1940 to 1971 have been recorded and mapped in Alameda County, mostly in the developed western parts of the county. About 85 percent of the landslides occurred on slopes greater than 15 percent. Over $5 million worth of damage was caused by landsliding in 1968-69; this cost averages out for that year to about $400 per developed acre ofland on slopes greater than 15 percent, or about $100 per dwelling unit. Rainfall that year, although not unusually high, was marked by a six-week rainy spell which triggered many slides, resulting in damages that were probably greater than usual. Strict grading ordinances and required soils and geologic investigations have been shown to reduce substantially the public and private costs of landsliding in other parts of California and probably would have the same effect in Alameda County. The areas of abundant recent landslides correlate partly with areas of abundant ancient landslide deposits.

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