On March 12th

The dam failed just before midnight on March 12, 1928, killing ~431 people; William Mulholland’s career ended with the disaster. The documented date is 1928-03-12. St. Francis Dam Disaster Site's past is on record — the entry belongs to the verified layer beneath whatever lore attaches. The fact is historically verified — the part of the file that doesn't need hedging. 'St. Francis Dam' documents

Three minutes before midnight on March 12, 1928, the St. Francis Dam — William Mulholland's pride — disintegrated, releasing a wall of water that killed more than 400 people down the Santa Clara River valley to the sea. It ended Mulholland's career, remains one of the worst civil-engineering failures in US history, and its ruins are now a National Memorial.