Theories and Root Causes

The unique geology of the canyon rocks under the surface was not obvious for the knowledge of the times and the concept of uplift under a dam's base is just becoming discussed nationwide by experts in the field and Mulholland would be counted in those circles in the 1920s.

As you drive through the San Francisquito canyon and its mouth and meeting with the Santa Clara River in Saugus, contemplate the 50 foot wall of water that ripped through this riverbed in the middle of the night in 1928. We run alongside and cross over its path as we navigate modern day Copper Hill or McBean. People living downstream for over 50 miles would be impacted by the relentless and difficult to imagine -- power of flowing water and debris.

So why did the dam fail? This is a difficult question to answer definitively but modern geologists and structural engineers agree on a few important factors:

1) The subterranean ancient landslide on the east abutment side of the dam became saturated and failed and this geology was not known at the time of construction of the dam.

2) The forces of uplift where the water itself, when stored in great volume actually significantly "lightens" the effective weight of the entire structure were not accounted for as they would be by the 1940s.

3) As the coroners inquest jurors found, the reliance upon only one man's decision making for design and construction of a structure so potentially dangerous was an error in judgement.

For more information on this and the dismissed theories of sabotage via dynamite or an earthquake being the cause and a host of others can be further examined in both Man Made Disaster by Charles Outland in 1963 or The St. Francis Dam Disaster Revisited by Nunis in 1995. We will involve ourselves more with the terror of the victims and stories of the survivors and the loss of property and leave the assignment of responsibilities and failures to you and the investigators.