A Roar in the Night
Just before midnight on March 12, 1928, a sound like thunder ripped through San Francisquito Canyon in California. Residents, jolted from their sleep, thought it was an earthquake.
In reality, the St. Francis Dam had collapsed, releasing over 12 billion gallons of water. Within minutes, a wall of water surged through the canyon, sweeping away everything in its path. By dawn, the flood had carved a 55-mile trail of devastation all the way to the Pacific Ocean.
The Vision of a Thirsty City
Los Angeles had grown rapidly by the early 20th century, outstripping its natural water supply. In response, William Mulholland—an Irish immigrant who had worked his way up from ditch digger to Chief Engineer—oversaw the creation of the Los Angeles Aqueduct in 1913.
As demand continued to grow, Mulholland led the construction of a massive storage reservoir: the St. Francis Dam. Completed in 1926, it stood 200 feet tall and could hold enough water to supply the city for two years.
Warnings Ignored
On the morning of March 12, dam keeper Tony Harnischfeger found a muddy leak on the dam’s western side. He contacted Mulholland, who arrived with his deputy to inspect the site. Convinced it was harmless runoff from nearby construction, they returned to Los Angeles.
That night, just before midnight, the dam gave way. Harnischfeger and his family were among the first to die. The flood destroyed entire towns, including Castaic, Saugus, Fillmore, and Santa Paula. Survivors clung to debris—trees, rooftops, even a water tank—to stay alive.
Aftermath and Accountability
In the light of day, the full extent of the tragedy emerged: more than 1,200 homes destroyed, thousands of livestock lost, and over 450 confirmed dead. Many more were never identified. A coroner’s inquest followed. Witnesses described earlier leaks and fears that had been dismissed.
On the stand, Mulholland accepted full responsibility, saying, “If there was an error in human judgment, I was the human.” Investigators ultimately concluded that the dam failed due to unstable geology, not deliberate wrongdoing.
Legacy in Concrete
Mulholland was cleared of charges but retired soon after. In later decades, new studies confirmed that the dam had been unknowingly built on an ancient landslide.
Today, remnants of the St. Francis Dam still lie in the canyon, along with a memorial marking one of California’s worst engineering disasters. The flood changed dam safety standards across the United States, ushering in reforms to prevent such a failure from happening again.
Just before midnight on March 12, 1928, a thunderous roar shook San Francisquito Canyon.
It wasn’t an earthquake—it was the collapse of the St. Francis Dam.
Within minutes, 12 billion gallons of water surged through the canyon, leaving destruction behind…🧵👇 pic.twitter.com/9RDE4KnAd4
— Detective Tiger's Stories (@TigerDetective) July 1, 2025