Dam failures have been fascinating me. Los Angeles' Kenneth Hahn State Park features a former reservoir and the remnants of a dam that failed in 1963, the Baldwin Hills dam.
See, land developer "Lucky" Baldwin had struck crude oil in the area in 1924 – and subsequent operations on the Inglewood Oil Field caused disturbances in the Pliocene- and Pleistocene-era marine sediments that formed the foundation of the dam and reservoir. Ground faulting and fault creep had already been happening when, in the mid-1950s, water was injected into the fields to get more oil. The more oil that was extracted, the more the ground sank, by as much as 12 feet. None of the oil companies or the LADWP knew it at the time, but engineers later discovered that those methods of oil extraction – and the resulting subsidence – would cause the dam lining to fail. The reservoir was doomed.
One afternoon in December 1963, signs of lining failure – namely, a gurgling noise – were followed by leakage through the dam's east abutment. It was slow enough to draw crowds and even a KTLA chopper news team – and the television coverage had plenty of time to alert local residents to evacuate before the dam breached, three hours later. The reservoir completely emptied, releasing nearly 250 million gallons of water in a 50-foot wall that washed away hundreds of homes and killed five people. The dam was never rebuilt and the reservoir never refilled with water – only with earth for the park that exists there today, which opened in 1984. For the easiest access point to the former dam site, head to the upper park parking lot (by the restrooms) and walk the "Bowl Loop") around the basin. There is a fee to enter on weekends and holidays only.