The St. Francis Dam "tombstone" — the section of the dam that remained standing after the dam broke March 12, 1928 — from the inside looking out (looking south).

This 2½x4-inch print, acquired at a flea market, shares the physical characteristics of this one, suggesting that it, too, may have been mass produced as a souvenir.

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.