Field of Science

March 12, 1928: The geological induced collapse of the St. Francis Dam

I like to see the job as geologist also as possibility to prevent damage and protect in a certain manner people, sometimes ignoring the geological structure and resulting problems of a construction sites can have disastrous consequences. Following the post in memoriam of the Stava dam collapse, a similar event from the New World, where ignoring the geological circumstances caused death and destruction:

At the end of the 19th century the city of Los Angeles was lacking an important factor limiting the economic development - the water supply was insufficient and couldn't satisfy the demand.

William Mulholland, an Irish immigrant and a very ambitious personality had managed to become a self-educated engineer and the superintendent of the Los Angeles Bureau of Water Works and Supply - he seemed the right man for the job to bring the needed water to the city.
So he planned and constructed a system of aqueducts that collected and redirected water from the Sierra Nevada to Los Angeles.
72 kilometres north from Los Angeles the main aqueduct ended in the San Francisquito Canyon, where two hydroelectric power stations were build. Mulholland decided to amply the original project and constructed a supplementary dam to regulate the water flow.

Fig.1. The completed St. Francis Dam (figure from CHAMP 1983).

The construction site in the the San Francisquito Canyon follows a tectonic lineament that separates conglomerates and sandstones with gypsum from alterated schists with layers of talcum. In addition to these very instable rocks surrounding the contact between the lithologies were lenses of serpentinites.

In 1926 the St. Francis dam was inaugurated, he was 61m high, with a span of 210m and at the base 50m thick. Soon after the completion of the dam water infiltrations were observed, but it seemed normal for such a large reservoir.
On the morning of the 12. May 1928 the technician Tony Harnischfeger observed a leak on the eastern side of the dam. Mulholland was informed and arrived at 10.30 p.m. to inspect the damage. The water was clear, sign that no sediment was eroded.

At 23.47 p.m. from the power station 1, situated 8 km above the dam, the personal contacted power station 2, situated 2 km under the dam - no problems were recorded.
At 23.57 p.m. a short power demise in Los Angeles was noted and the electric power lines in the Canyon got interrupted -
45 billions liters of water had smashed the dam and were flowing in the canyon.

Fig.2. The remains of the St. Francis Dam (figure from CHAMP 1983).

The resulting waves overrun the highway 126 in the Santa Clara Valley, destroying 50 cars and killing 125 people. The flood finally reached the pacific coast and flowed in the ocean, 70 km distant from the San Francisquito Canyon.


CHAMP, C. (1983): Planet Earth - Flood. Time-Life-Books. Amsterdam: 176


  1. Nice set of pdf's about the St Francis dam failure.

  2. Great stuff. I've been studying up on this stuff since I injured my leg from some fire damage in Honolulu, so I appreciate you posting.

  3. Wonderful information. The St Francis dam story has so many aspects to it - engineering, geology, history, economic...I've been researching the resulting floods here and found it fascinating.

  4. The leaks Tony Harnischfeger saw were actually on the west abutment, right below the wing dike, near the thrust block.

    Been doing intensive study on the St. Francis Dam for 30 years, and I go out to the site a lot.

  5. The leaks Harnischfeger saw were actually on the WEST end and abutment of the dam, near the thrust block and the start of the wing dike. Mulholland and Van Norman arrived at 10:30 AM the morning of March 12, 1928, and stayed for a few hours. Van went down to the base of the thrust block near the dam's groin and used a clear water tumbler, a drinking glass, to sample the leaking water, which he declared to be "clear."

    I've been studying this story intensively for over 30 years, and have been to the dam site many times. The references you cite are poorly researched and not well-fleshed-out. The best material on the subject to date has been published by Dr. J. David Rogers, one of the world's leading experts on the disaster. Charles Outland published the remarkable volume MAN-MADE DISASTER years ago, and it's research is impeccable.
    I've also published some work on the story, Google A TEST OF INTEGRITY by Pony Horton.

  6. The leaks Tony Harnischfeger saw were actually on the west abutment, right below the wing dike, near the thrust block.

    Been doing intensive study on the St. Francis Dam for 30 years, and I go out to the site a lot.


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