Planning and design
Mulholland, a self-taught civil engineer, had risen through the ranks of the Los Angeles Department of Water and Power, then called the Bureau of Water Works and Supply, and had quickly established himself as having a penchant for thriftiness, an enormous capacity for innovation, and the ability to complete difficult projects on-time and on-budget. These traits undoubtedly aided him in designing and building the Los Angeles Aqueduct in 1913, which at the time was the longest aqueduct in the world, bringing water 233 miles (380 km) from the Owens Valley to the city of Los Angeles.
The rapid growth of Los Angeles demanded a larger water supply, so a series of small reservoirs were built in the 1920s to provide the rapidly-expanding city with a water supply in the event of a drought or damage to the aqueduct, but the need for larger reservoirs was obvious.
In the process of designing and building the Los Angeles Aqueduct, Mulholland had considered sections of San Francisquito Canyon—beginning about 30 miles (50 km) north of Los Angeles—as a potential dam site in 1911. Conveniently, the Los Angeles Aqueduct ran along the canyon, and two generating stations in the same canyon used aqueduct water to provide power for Los Angeles. To Mulholland, the location appeared ideal—the reservoir would provide ample water for Los Angeles in the event of a drought or if the aqueduct was damaged by an earthquake or sabotage.
In 1924, construction was quietly begun on the dam so as not to attract the attention of the farmers dependent on the water of San Francisquito Creek. Additionally, the Los Angeles Aqueduct was the target of frequent sabotage by angry farmers and landowners in the Owens Valley, and Mulholland was eager to avoid the kind of expensive and time-consuming repairs which plagued the Los Angeles Aqueduct. The dam was named the "St. Francis", an anglicized version of the name of the canyon in which it was built.
Immediately after construction had begun in 1924, Mulholland decided to raise the height of the dam 10 feet (3 m), increasing the capacity of the reservoir from 30,000 to 32,000 acre-feet (39 million cubic meters) of water, and Mulholland made minor changes in the dam's design to accommodate the additional height.
In July 1925, when the dam was roughly half-completed, Mulholland added an additional 10 feet (3 m), bringing the dam's new height to 195 feet (59 m) and increasing the reservoir's capacity to more than 38,000 acre-feet (47 million cubic meters) The dam's new height necessitated the construction of a "wing dike" along the top of the ridge of the western abutment to prevent water from spilling over the ridge.
Throughout 1926 and 1927, several temperature and contraction cracks appeared in the dam as the reservoir filled. The cracks and leaks were inspected by Mulholland and his assistant, Harvey van Norman, and judged to be within expectation for a concrete dam the size of the St. Francis.
Through the closing months of 1927 to March 1928 the reservoir rose steadily, and uneventfully. On March 7, 1928 the reservoir had reached full capacity; Mulholland ordered that no more water be turned into the St. Francis. In the same week, allegedly, a few motorists traveling on the road along the east shore of the reservoir reported cracks and a sagging in the roadbed near the dam's east abutment. By one account, given after the dam's collapse, the roadbed had sagged almost 1 foot (0.30 m).
On the morning of March 12, the dam keeper, Tony Harnischfeger, discovered a new leak and immediately alerted Mulholland because he took the muddy brown color of the water to be an indication the leak was eating away the foundations of the dam. Mulholland and Van Norman inspected the new leak. Convinced the leak was relatively minor and normal for a concrete dam, Mulholland pronounced the dam safe.
Three minutes before midnight on March 12, 1928, the St. Francis Dam catastrophically failed. There were no eyewitnesses to the dam's collapse, but a motorcyclist named Ace Hopewell rode past the dam and reported feeling a rumbling and the sound of "crashing, falling blocks," after riding about a half-mile (800 m) upstream. He assumed this was either an earthquake or another one of the landslides common to the area, not realizing he was the last person to have seen the St. Francis Dam intact, and survive.
Dam keeper Harnischfeger and his family were, most likely, the first casualties caught in the flood wave, also called dam break wave, which was at least 125 ft (38 m) high when it hit their cottage in San Francisquito Canyon, approximately 1/4 mile (400 m) downstream from the dam. Thirty minutes before the collapse a motorist passing by the dam also reported seeing lights in the canyon below the dam —the dam itself did not have lights—suggesting Harnischfeger may have been inspecting the dam immediately prior to its failure. The body of Leona Johnson, who lived with the Harnischfegers (and has been often and mistakenly reported to be Harnischfeger's wife) was found fully clothed and wedged between two blocks of concrete near the broken base of the dam. Neither Harnischfeger's body nor that of his six-year-old son, Coder, were ever found.
As the dam collapsed, twelve billion U.S. gallons (45 billion liters) of water surged down San Francisquito Canyon in a dam break wave, demolishing the heavy concrete walls of Power Station Number Two (a hydroelectric power plant), and destroying everything else in its path. The flood traveled south down San Francisquito Canyon, flooding parts of present-day Valencia and Newhall. The deluge then turned west into the Santa Clara River bed, flooding the towns of Castaic Junction, Fillmore, and Bardsdale. The flood continued west through Santa Paula in Ventura County, emptying its victims and debris into the Pacific Ocean at Montalvo, 54 miles (87 km) from the reservoir and dam site. When it reached the ocean at 5:30 a.m., the flood was almost two miles (3 km) wide, traveling at a speed of 5 miles (8 km) per hour. Bodies of victims were recovered from the Pacific Ocean, some as far south as the Mexican border.
Telephone operators in Fillmore (notably Louise Gipe) and two motorcycle policemen in Santa Paula notified people in their homes of the danger, until the rising floodwaters forced their retreat.
The day after the disaster the front page of the Los Angeles Times ran four stories, including aerial photos of the obliterated dam, the city of Santa Paula after its wake and a partial list of the dead. It also set up a Times Flood Relief Fund, to receive donations from around the country. The Times also reported that Mullholland and his assistant, Chief Engineer Van Norman, issued a statement, saying, "I would not venture to express at this time a positive opinion as to the cause of the St. Frances Dam disaster." Mullholland and Van Norman arrived on the scene of the dam break around 2:30am the morning the 13th, "...and saw at once that the dam was completely out and that the torrential flood of water from the reservoir had left an appalling record of death and destruction in the valley below." In the article, Mullholland stated he believed there had been major movement in the hills forming the western buttress of the dam. However, he added that three eminent geologists, Robert Hill, C. F. Tolman and D. W. Murphy had been hired to determine if the actual cause of the breakage of the dam was due to some type of major movement. It was noted that there were no tremors reported at seismograph stations and an earthquake could be ruled out as the cause of the break.
The dam broke into several large pieces, some of which were carried almost 1/2 mile (800 m) downstream, while the center section of the dam—nicknamed "The Tombstone"—remained standing (see photo in ). Two months after the collapse, 18-year-old Lercy Parker fell to his death while climbing the ruins, and in the following months, the upright section was toppled with dynamite and the remaining blocks demolished with bulldozers and jackhammers to discourage sightseers and souvenir hunters from exploring the ruins. Although the west wing dike remained intact, it was used by Los Angeles firemen to gain experience of using explosives on building structures. The St. Francis Dam was not rebuilt, although Bouquet Reservoir in nearby Bouquet Canyon and Castaic Dam in the town of Castaic were subsequently built as replacements for the St. Francis Dam (in 1934 and 1973, respectively).
To this day, the exact number of victims remains unknown. The official death toll in August 1928 was 385, but the bodies of victims continued to be discovered every few years until the mid-1950s. Many victims were swept out to sea when the flood reached the Pacific Ocean and were not discovered until they washed ashore, some as far south as the Mexican border. The remains of another victim were found deep underground near Newhall in 1992, and the current death toll is estimated to be more than 600 victims (excluding the itinerant farm workers camped in San Francisquito Canyon, the exact number of which will never be known).
Immediately following the disaster, Mulholland said he “envied those who were killed” and went on to say, “Don’t blame anyone else, you just fasten it on me. If there was an error in human judgment, I was the human, and I won't try to fasten it on anyone else.” At the Coroner's Inquest, the leaks Tony Harnischfeger had spotted and reported to Mulholland were cited as evidence of the dam leaking the day before the break, and that both the LADWP and Mulholland were aware of them. Mulholland admitted being at the dam the day before the break, but had noticed nothing out of the ordinary, testifying that leaks in dams—especially in dams the size of the St. Francis—were not unusual.
The Los Angeles Coroner's Inquest concluded the disaster was primarily caused by the paleomegalandslide on which the eastern abutment of the dam was built, but would have been impossible for the geologists of the 1920s to detect. Indeed, two of the world's leading geologists at the time, John C. Branner of Stanford University and Carl E. Grunsky, had found no fault with the San Francisquito rock. Therefore, the jury determined responsibility for the disaster lay with the governmental organizations which oversaw the dam's construction and the dam's designer and engineer, William Mulholland, but cleared Mulholland of any charges, since neither he nor anyone at the time could have known of the instability of the rock formations on which the dam was built. The hearings also recommended, "the construction and operation of a great dam should never be left to the sole judgment of one man, no matter how eminent."
Soon after the inquest, Mulholland retired from the LADWP and retreated into a life of self-imposed isolation. He died in 1935, at the age of 79.
In response to the St. Francis Dam disaster, California Legislature created a dam safety program in 1929 and the California Department of Water Resources was created in 1956 by Governor Goodwin Knight following severe flooding across Northern California in 1955, combining the Division of Water Resources of the Department of Public Works with the State Engineer's Office, the Water Project