Human Error

The St. Francis Dam was meant to be a triumph, a testament to the engineering prowess of Los Angeles’ waterworks in the early 20th century. Designed to store water from the Owens Valley and supply a rapidly expanding city, it was a vital component of the Los Angeles Aqueduct system. Built between 1924 and 1926 under the supervision of William Mulholland, the city’s legendary but self-taught water engineer, the dam was constructed in San Francisquito Canyon, about 40 miles northwest of downtown Los Angeles. It was only the second concrete gravity dam built by the Los Angeles Bureau of Water Works and Supply, modeled after the earlier Mulholland Dam in Hollywood.

The design was ambitious but flawed. The original height of the dam was raised twice during construction—without increasing the base width—creating a dangerous imbalance between structure and support. The site itself was chosen for convenience rather than stability; it rested on rock formations that would later prove disastrous. The left abutment sat on ancient landslide material, and the right abutment on fragile schist rock—geological time bombs waiting for the right conditions to collapse. Even before the dam was completed, cracks and leaks appeared, which Mulholland dismissed as routine. His experience with embankment dams had not prepared him for the peculiar demands of concrete gravity dams. No independent review was conducted, and safety margins that should have been built into the design were overlooked in favor of speed and cost efficiency.

For two years, the dam held back its reservoir, slowly filling to capacity. By March 7, 1928, the water level was within inches of the spillway. The dam had never held so much water before, and the pressures building within its foundation were about to reach a catastrophic breaking point.

On the evening of March 12, 1928, Tony Harnischfeger, the dam’s keeper, noticed a muddy leak on the western abutment, an ominous sign that something was wrong. He immediately called for an inspection. Mulholland himself, along with his assistant Harvey Van Norman, arrived and examined the site. They dismissed the leakage as nothing unusual, convinced that the dam was structurally sound. Less than 12 hours later, at precisely 11:57 p.m., the St. Francis Dam disintegrated in a sudden and horrifying collapse.

A wall of water—over 12.4 billion gallons—rushed down San Francisquito Canyon, a roaring tsunami of destruction. The first to die were Harnischfeger, his family, and workers at Powerhouse No. 2, who were crushed and swept away by a 140-foot-high surge. Within minutes, the flood engulfed everything in its path, racing toward the Santa Clara River Valley. Entire towns, including Castaic Junction, Fillmore, and Bardsdale, were devastated. Homes were torn from their foundations, bridges were obliterated, and railroad tracks were twisted into grotesque shapes. The flood surge remained powerful for over 50 miles, until it finally emptied into the Pacific Ocean near Ventura.

The human toll was staggering. Officially, 431 people were reported dead, but the true number is likely higher, as many bodies were never recovered, and transient workers in the area were uncounted. The debris field stretched for miles, carrying everything from uprooted trees to automobiles, and even entire buildings. Some victims were found buried under mud and debris weeks later, as far as the ocean shoreline. It remains one of the deadliest man-made disasters in U.S. history.

In the immediate aftermath, emergency crews and volunteers worked tirelessly to recover bodies, aid survivors, and clear the wreckage. The political fallout was swift. Investigations began almost immediately, and while many theories emerged, the prevailing conclusion was that the dam had been fatally flawed from the start. The geological instability of the site, the flawed engineering design, and the last-minute height increases all contributed to its failure. Mulholland, once hailed as a visionary, saw his career end in disgrace. At the inquest, he took full responsibility, saying, “If there was a human error, I was the human.” He retired soon after, living out the rest of his life in relative obscurity.

The disaster also had lasting consequences for dam engineering and public works safety. The collapse of the St. Francis Dam led to stricter regulations for dam construction, requiring geologic surveys, independent reviews, and structural reinforcements. The Mulholland Dam in Hollywood, built with the same principles as the St. Francis, was immediately reinforced with an earthen dam for additional support. More broadly, the event led to the establishment of state and federal dam safety programs, ensuring that such a catastrophe would never happen again.

Today, the ruins of the St. Francis Dam are a somber reminder of hubris, ambition, and the consequences of neglecting safety in the pursuit of progress. What was meant to be a symbol of Los Angeles’ growth became a graveyard, its legacy carved into the canyon walls where water once flowed. The story of the St. Francis Dam is not just a tale of disaster, but a lesson in engineering, responsibility, and the cost of ignoring the warning signs.