The dam vanished nearly 70 years ago, but the fury and death that its failure wrought are still haunting.

Geological engineer J. David Rogers may have finally unraveled the lingering mystery of one of Ventura County's greatest disasters: the collapse of the St. Francis Dam, which killed 450 people on March 12-13, 1928.

By using computer simulations and other modern techniques, Rogers, in a forthcoming book, concludes that the dam collapsed because it was built partly on an ancient landslide, which started to move again under the weight of the dam.

He discarded the previous theory that the dam's foundation had absorbed water, causing it to weaken.

Along the way, Rogers also discarded another long-held notion: that blame for the disaster belonged to the dam's creator, William Mulholland.

The dam, situated northeast of Castaic in Los Angeles County near the Ventura County line, collapsed at 11:57 p.m. on March 12, 1928, causing an avalanche of water to sweep 54 miles west through Santa Clara Valley and into the Pacific Ocean.

It killed about 450 people, half of them Ventura County residents living in low-lying areas near Piru, Fillmore, Santa Paula and Ventura. It demolished 1,200 houses and washed out 10 bridges. The city of Los Angeles paid $4.8 million in damage claims.

Among calamities, it ranks with the 1906 San Francisco earthquake and fire, which killed 452 people [sic; an estimated 3,000 people perished in the San Francisco tragedy].

Rogers, who teaches at UC Berkeley, spent 15 years researching and writing the nearly 200-page book that is being published by the Ventura County Museum of History and Art and the Historical Society of Southern California.

"The St. Francis Dam Disaster Revisited," which will be available for sale within four weeks, features more than 50 previously unpublished photographs of the disaster.

"It was a long and arduous project, but one that I had a lot of fun doing," Rogers said.

Rogers said he based much of his research on the 1963 book, "Man-Made Disaster," by the late Santa Paula journalist Charles Outland.

But unlike Outland, Rogers took a more scientific approach to his research, said Thomas Andrews, executive director of the Historical Society of Southern California.

The new book "balances the historical and scientific issues relating to the event," Andrews said. "I think this book may be as close as we will ever get to the causes of the disaster."

In addition to Outland's book, Rogers said he used information from a research paper by a retired Stanford University professor, Bailey Willis, who speculated about the possibility of an ancient mudslide in the area.

As he tried to make sense of the tragedy, Rogers said, the most unexpected revelation was his new opinion of Mulholland. When he began the project, Rogers shared the common belief that Mulholland was responsible for the dam's failure.

Mulholland oversaw construction of the dam as chief engineer for the Los Angeles Bureau of Water Works and Supply, a forerunner of the Department of Water and Power. The dam had been designed to create a 12-billion-gallon reservoir for Los Angeles residents.

"I first saw Mulholland as a villain, a fool. But now I see him as a man of tremendous professional integrity," Rogers said. "Considering the technology available at the time, there was no way he or any of the people working for him would have known about this gigantic landslide."

The story of the Mulholland family's personal pain over the collapse is also included in the book, in a chapter written by the engineer's granddaughter, Catherine Mulholland.

"My parents' generation had been stunned into silence by the tragedy, as if even to speak of it was too painful to endure," Catherine Mulholland writes. Now, "a lifetime later, (the story) still has the power to wrench my heart and soul."