San Francisquito Canyon Road, Copper Hill, Santa Clarita, Los Angeles County, California, 91354, United States
Los Angeles Department of Water and Power
Wikipedia[1] places the failure two and a half minutes before midnight on 12 March 1928; ASDSO's dam-failure case study, the St. Francis Dam National Memorial Foundation and PBS SoCal[4] all give the night of 12 March 1928 (PBS notes the flood reached the sea at 5:30 a.m. on 13 March).
The St. Francis Dam in San Francisquito Canyon failed just before midnight on 12 March 1928, sending a flood about 55 miles to the Pacific and killing more than 400 people.