St Francis Dam Failure, 12 March 1928. Failed catastrophically upon its first full filling, near midnight, killing at least 450 people. Seepage (dirty water) was observed the day of the failure. A massive landslide occurred in the dams left abutment, comprised of schist.
“Greatest American civil engineering failure in the 20th century.”
Historical Society of Southern California: St. Francis Dam Disaster.
Excellent Photo Display at: St. Francis Dam collapse – Framework – Photos and Video – Visual Storytelling from the Los Angeles Times.
Type: Concrete Gravity Thick Arch Dam, Maximum Height = 195 feet, Storage (at time of failure) = 38,000 acre-feet