19. The collapse of the St. Francis Dam in 1928 was one of the greatest civil engineering disasters in 20th century American history, precipitating the second-largest loss of life in Californian history.
The St. Francis Dam, designed and built between 1924 and 1926 by the Los Angeles Bureau of Water Works and Supply, was created to provide a regulatory and storage reservoir for the expanding Californian city. Serving as an a crucial component of the Los Angeles Aqueduct, the dam project, led by William Mulholland, was located in the San Francisquito Canyon of the Sierra Pelona Mountains, approximately 40 miles northwest of L.A. After two years of operation, at 11:58 pm on March 12, 1928, the dam suddenly suffered a catastrophic failure. Within 70 minutes, all 12.4 billion gallons of reservoir water had been emptied to create a 140-foot wave that swept across the surrounding landscape.
Traveling at speeds of 29 kilometers per hour, the gigantic wave continued until it emptied into the Pacific Ocean. Bodies were recovered as far south as the Mexican border, with an estimated 431 people believed to have been killed by the dam’s collapse. Subsequent investigations blamed the incident on “defective foundations”, asserting that a consistent leak had infiltrated the foundations, gradually eroding the supporting concrete until the structure could no longer sustain its own weight. Despite the coroner recording “an error in engineering judgment in determining the foundations…and deciding on the best type of dam to build there”, Mulholland was nonetheless cleared of any criminal wrongdoing.