Prado Dam is an earth-fill dry dam across the Santa Ana River at the Chino Hills near Corona, California in Riverside County with the resulting impounded water creating Prado Flood Control Basin reservoir. The U.S. Army Corps of Engineers built the dam in Lower Santa Ana River Canyon. Its primary purpose is flood control and it is the downstream element of the Santa Ana River's flood control system, which is a natural constriction about 30.5 mi upstream from the ocean. The area upstream from the dam contains 2255 sqmi of the watershed's 2650 sqmi. The dam's construction was authorized in 1936 and the flood of 1938 demonstrated its necessity. Construction was completed in 1941. Prado Flood Control Basin also provides water storage for groundwater recharge operations.

Failure threat

On January 14, 2005, after days of heavy rain, water began seeping through an earthen extension. Authorities released water in order to relieve pressure and sent a flood warning to areas downriver of the dam. Over 3,000 residents were evacuated from their homes for nearly twenty-four hours for fear of flooding. The gymnasium at Corona High School was converted by the American Red Cross into a temporary shelter.

Upgrades

As of 2005 work to increase the downstream channel's capacity from 5000 to 30000 ft3 per second is ongoing. The total costs of the improvements is estimated at $400 million.