William Mulholland's great St. Francis Dam broke at three minutes before midnight on March 12, 1928, sending a 180-foot-high wall of water crashing down San Francisquito Canyon and claiming approximately 470 lives by the time the floodwaters reached the Pacific Ocean at Ventura.

In this photograph, mourners inter the bodies of dam victims in the Ruiz family cemetery, located approximately six miles south of the dam site. A family of farmers in the canyon since the mid-1800s, six Ruiz family members — Rosaria and Enrique Ruiz and four of their children, ages 8 to 30 — perished in the disaster.

It was the second-worst disaster in California history, second only to the great San Francisco earthquake and fire of 1906.

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.