12 March 1928

In California, the St. Francis Dam fails; the resulting floods kill 431 people.

The St. Francis Dam was a concrete gravity-arch dam located in Los Angeles County, California, USA. It was designed and built by the renowned civil engineer William Mulholland and completed in 1926. However, on March 12, 1928, the dam catastrophically failed, resulting in one of the worst civil engineering disasters in American history.

The failure was caused by a combination of factors, including the design of the dam, the materials used in its construction, and the geological conditions of the site. The dam was built on a geologically unstable foundation of conglomerate rock, which was prone to cracking and movement. Over time, the movement of the rock caused the dam to develop cracks, which eventually led to its collapse.

On the night of March 12, 1928, the dam failed, releasing a wall of water that was up to 140 feet high and 2.5 miles wide. The floodwaters swept through the Santa Clara River Valley, destroying everything in their path. The disaster resulted in the deaths of at least 431 people, making it one of the deadliest engineering failures in US history.

The failure of the St. Francis Dam led to significant changes in the design and construction of dams, including the development of new materials and testing methods. The disaster also led to increased government oversight of dam construction and maintenance, as well as a greater awareness of the importance of safety in engineering.