In late February 1928, about two weeks before the dam broke, 18-year-old Hetta Laurena Carter shot this photograph of a mortar box, hoe, bucket and garden hose, used to plug a leak with "sloppy cement."

In a televised 2006 interview with dam historian Keith Buttelman (watch it here), Carter said:

"It was end of February (1928), which would make me 18 years old. I had been driving for a while, and it was just fun to drive. My dad had an old Chevy, and I drove the old Chevy all over the country.

"As I sat there, I wondered what in the world they were doing up on the corner of the dam. My father was a cement contractor, and I thought, 'That looks like cement up there.'

"I walked a little closer, and it was a half a sack of cement in the mortar box. The box also held a wooden hoe and a bucket, and the tip of a garden hose. The hose was down the side of the dam, so I immediately guessed that they were making sloppy cement in the mortar box, pouring it down the hose to (fill) a small leak that was on the side of the dam, about halfway down the dam."

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.