Looking back (north) at the empty reservoir in San Francisquito Canyon, shortly after the St. Francis Dam collapsed on March 12-13, 1928.

The dam impounded 12.5 billion gallons of the City of Angels' drinking water. The line between dark and light represents the pre-disaster water level. The concrete dam would have been just out of view at the bottom of this photo.

4x6-inch BW film transparency (larger than 4x5). Date, photographer and original purpose of photograph unknown.

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.