Geology of the Saint Francis dam site

The St. Francis dam was situated in San Francisquito Canyon, about 45 miles north-northwest of Los Angeles and 9 miles north of Saugus. (See Fig. I). Its purpose was to form a storage reservoir into which surplus water was delivered from the Los Angeles aqueduct. The capacity of the reservoir was 38,000 acre-feet. About 9 miles below the dam San Francisquito Canyon opens into the broad fertile Santa Clara Valley which continues westward for 44 miles to the Pacific Ocean.