7. St. Francis Dam

Location: Los Angeles, CA

Year of Fail: 1928

The second greatest loss of life in California state history, St. Francis dam suffered a catastrophic failure in 1928, releasing 12 billion gallons of water in a 125-foot wave that killed more than 600 people. Almost two miles wide and traveling five miles per hour, victims and debris were emptied into the Pacific Ocean, 54 miles from the reservoir and dam site. Structural additions that increased water capacity, cracks ignored by engineers and the instability of the rock under the dam were to blame. On the morning of the failure, the dam keeper reported a new leak that appeared to indicate water eroding the foundations of the dam, but The Department of Water and Power deemed the dam safe.