At 11:56 PM on March 12, 1928, the concrete arch St. Francis Dam was a key element of the Los Angeles (California) Aqueduct. It was designed and constructed by the City of Los Angeles' Department of Water and Power (LADWP) to create a reservoir to store water brought via the Aqueduct from the Owens Valley in east central California to serve the burgeoning city of Los Angeles. It was a concrete gravity arch dam located about 40 miles northwest of Los Angeles on San Francisquito Creek near the present day city of Santa Clarita, California. At 11:57 PM it collapsed catastrophically, releasing 12 billion gallons of flood waters downstream that reached a depth of 140 feet with average velocities estimated at 26 feet per second. By 5:30 AM on March 13 flood waters reached the Pacific Ocean at Montalvo (near Ventura), California. The flood killed more than 450 people and was the worst civil engineering failure in U.S. history.