Pacoima Dam is a concrete arch dam on Pacoima Creek in the San Gabriel Mountains, in Los Angeles County, California. The reservoir it creates, Pacoima Reservoir, has a capacity of Built by the Los Angeles County Flood Control District, which became part of the Department of Public Works, it was completed in 1928. At the time, the 371 foot (113m) high dam was the tallest arch dam in the U.S. The dam is situated approximately northeast of Sylmar, above the San Fernando Valley. Instrumentation As construction of Pacoima Dam began, the County of Los Angeles hired Roy W. Carlson as their concrete and soil testing engineer. He developed the world's first strain meter which could be embedded in concrete. He also developed an adiabatic calorimeter and electrical-resistance thermometers to find why the temperature of concrete increased during curing and how best to avoid cracking caused by these stresses. Earthquake monitoring The Pacoima Dam withstood, but was damaged by the very strong (>1 g) ground movement which occurred during both the 1971 San Fernando and 1994 Northridge earthquakes. Because of concerns about the stability of the dam and especially its response to potential future earthquakes, the County of Los Angeles, with the technical support of the USGS, began monitoring the dam using continuous GPS. See also Angeles National Forest List of dams and reservoirs in California List of lakes in California References External links Image of workers at the bottom of a canyon at the Pacoima Dam site working on wood framing and concrete pouring, 1926. Los Angeles Times Photographic Archive (Collection 1429). UCLA Library Special Collections, Charles E. Young Research Library, University of California, Los Angeles. Los Angeles County Department of Public Works dams Arch dams San Gabriel Mountains San Fernando Valley Dams completed in 1929