St. Francis Dam

The St. Francis Dam was a concrete gravity dam located in San Francisquito Canyon in northern Los Angeles County, California that was built between 1924 and 1926 to serve the city of Los Angeles's growing water needs. It failed catastrophically in 1928 due to a defective soil foundation and design flaws, unleashing a flood that claimed the lives of at least 431 people. The collapse of the dam is considered to have been one of the worst American civil engineering disasters of the 20th century, and remains the 3rd-greatest loss of life in California's history, exceeded only by the 1906 San Francisco earthquake and fire and the Great Flood of 1862. The St. Francis Dam was built to create a large regulating and storage reservoir that was an integral part of the Los Angeles Aqueduct. It was located in San Francisquito Canyon of the Sierra Pelona Mountains, about northwest of downtown Los Angeles, and approximately north of the present day city of Santa Clarita, California. The dam was designed and built by the Los Angeles Department of Water and Power, then named the Bureau of Water Works and Supply. The department was under the direction of its general manager and chief engineer, William Mulholland. The disaster effectively ended Mulholland's career. In the early years of Los Angeles, the city's water supply was obtained from the Los Angeles River. This was accomplished by diverting water from the river through a series of ditches called zanjas. At that time, a private water company, the Los Angeles City Water Company, leased the city's waterworks and provided water to the city. Hired in 1878 as a zanjero (ditch tender), William Mulholland proved to be a brilliant employee who, after doing his day's work, would study textbooks on mathematics, hydraulics and geology, thereby teaching himself geology and engineering. Mulholland quickly moved up the ranks of the Water Company and was promoted to superintendent in 1886. In 1902, the City of Los Angeles ended its lease with the Water Company and took control over the city's water supply.