Ruins of the St. Francis Dam shortly after its collapse on the night of March 12, 1928, showing the wing dike at left, the "tombstone" at right and the empty reservoir in the background.

Photo by George Watson, possibly shot on March 13 around the same time he shot the famous photograph that appeared with the Los Angeles Times' initial story about the disaster.

4x5 negative from the Watson Archive.

Construction on the 600-foot-long, 185-foot-high St. Francis Dam started in August 1924. With a 12.5-billion-gallon capacity, the reservoir began to fill with water on March 1, 1926. It was completed two months later.

At 11:57:30 p.m. on March 12, 1928, the dam failed, sending a 180-foot-high wall of water crashing down San Francisquito Canyon. An estimated 411 people lay dead by the time the floodwaters reached the Pacific Ocean south of Ventura 5½ hours later.

It was the second-worst disaster in California history, after the great San Francisco earthquake and fire of 1906, in terms of lives lost — and America's worst civil engineering failure of the 20th Century.