San Antonio Dam is an embankment flood control and debris dam on San Antonio Creek in San Bernardino County, California, about north of Ontario. The dam was authorized by the Flood Control Acts of 1936 and 1938 as part of a major program to provide flood protection in the Santa Ana River system. Construction began in April 1952 and finished in May 1956. The dam controls runoff from a rugged catchment area of in the San Gabriel Mountains.
The dam was built by the Los Angeles District of the U.S. Army Corps of Engineers. The dam is long, high above the foundation, and above the riverbed. The main embankment contains of material. The reservoir behind the dam is usually dry, but can fill with up to of water after large flooding events. A concrete overflow spillway on the west side prevents overtopping and drains to the San Antonio and Chino Creek channels, which were lined with concrete between 1956 and 1960 to protect against such an event.
A project has been underway since 2012 to remediate seepage problems at the toe of the dam during heavy rainstorms. The dam is considered a high hazard structure.
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