Why the St. Francis Dam Really Collapsed

On the morning of March 12, 1928, William Mulholland, the engineer who built Los Angeles' water system, inspected a new leak at the St. Francis Dam and judged it safe. A few minutes before midnight, the dam failed. Its flood travelled about 52 miles to the Pacific and killed more than four hundred people. This is an investigation into why. We look at what the dam was standing on, how it was changed during construction, the water pressure pushing up from beneath it, the warning signs in the days before the failure, and how the 1928 investigations and later engineering analysis explain the collapse differently — including the question that is still debated: which side gave way first. CASE #016 — The Strange File Real places. Strange stories. One explanation. CHAPTERS 0:00 The dam that failed that night 1:01 Why the dam existed 1:58 The structure and the ground beneath it 3:28 The warning signs 4:51 The night of the collapse 6:27 The investigation 8:29 The cost and the legacy 9:20 So why did it fail? SOURCES Report of the Commission Appointed by Governor C. C. Young to Investigate the Causes Leading to the Failure of the St. Francis Dam (1928): https://authors.library.caltech.edu/r... J. David Rogers, The 1928 St. Francis Dam Failure and Its Impact on American Civil Engineering: https://web.mst.edu/~rogersda/st_fran... J. David Rogers, Reassessment of the St. Francis Dam Failure (1992): https://damfailures.org/sites/default... ASDSO case study: https://damfailures.org/case-study/st... USGS, St. Francis Dam Disaster: https://www.usgs.gov/media/images/st-... Coroner's jury verdict (1928), via SCV History: https://scvhistory.com/scvhistory/sfd... Engineering News-Record: https://www.enr.com/articles/61151-to... California DWR, History of California Dam Safety: https://water.ca.gov/Programs/All-Pro... Victim research by Ann Stansell, via SCV History: https://cougarnews.com/scvhistory/ann... IMAGE CREDITS (Wikimedia Commons) H. T. Stearns, USGS (public domain): https://commons.wikimedia.org/w/index... · https://commons.wikimedia.org/w/index... Los Angeles Herald-Examiner (public domain): https://commons.wikimedia.org/w/index... Los Angeles Daily News / UCLA Library (CC BY 4.0): https://commons.wikimedia.org/w/index... Konrad Summers (CC BY-SA 2.0): https://commons.wikimedia.org/w/index... · https://commons.wikimedia.org/w/index... Imveracity (CC BY-SA 4.0): https://commons.wikimedia.org/w/index... Imveracious (CC BY-SA 3.0): https://commons.wikimedia.org/w/index... Maps: © OpenStreetMap contributors Scenes marked "Illustrative reconstruction" are AI-generated illustrations, not photographs of the real dam or event. Maps and diagrams are simplified. #StFrancisDam #EngineeringHistory #TheStrangeFile