Construction on the ill-fated St. Francis Dam began in August of 1924 and the first water was pumped into the reservoir on March 1st, 1926. Built to hold a surplus water supply for the city of Los Angeles, its location attacked as being unstable and dangerous by several geologists and engineers at the time. Despite this, and perhaps the Los Angeles Department of Water & Power's (DWP) chief engineer, William Mulholland's own knowledge of this possible and eventual cause of the dam's failure, it was put off as a minor issue, since there had been dams built in more precarious areas, so construction continued.
One might ask as to why this dam was even built when the then newly constructed Los Angeles Aqueduct had the capability to deliver four times as much water as the city's population demanded. Mulholland and the DWP's willingness the construct this dam in such haste, lies in the boiling arguments between the city and the farmers of the Owens River Valley.
In the years precluding the construction of the Los Angeles Aqueduct, the city of Los Angeles and managed to secretly buyout all the water rights the area. This caused a great deal of contempt towards Los Angeles from the farmers there whose water supply decreased and subsequently their crop yield as a well. This resulted in what one might call "vigiliante justice" as for many years the aqueduct was often sabotaged, cutting off the precious liquid that the city needed to survive.
What would prove to be a key reason as to prove the necessity of the St. Francis Dam occurred on May 27th, 1927 when tensions between the farmers and the city finally broke over. At No Name Canyon, about ten miles south of the desert community of Little Lake was a inverted syphon of the aqueduct. Here a massive charge of explosives was set and more than 450 feet of the aqueduct pipeline was destroyed, and several nights later, an additional 60 feet of pipeline were destroyed near a city power plant in Big Pine Creek. Amazingly the city's water supply was not disrupted, thanks to the near-capacity St. Francis Reservoir.
After the collapse of Owens Valley banks, the attacks on the aqueduct ended once and for all, and subsequently, the St. Francis Reservoir began refilling at the end of 1927 and reached its peak on the day of its failure, March 12th.
At 11:57 ½ PM March 12th, DWP power reciving stations 'A' and 'B' had a sharp drop in voltage for 2 seconds, the lights in Los Angeles flickered for a moment, and the Southern California Edison line to Lancaster failed. The St. Francis Dam was out.
The waters of the St. Francis Reservoir finally met the Pacific Ocean at Oxnard more than 3 hours from the initial dam break. Castaic Junction, the Southern California Edison camp, Kemp, and the cities of Camulous, Piru, Fillmore, Barsdale, Sespe, Santa Paula, were completed destroyed by the flood waters, and at the end, the death toll was at 450.
The disaster destroyed the reputation of Mulholland and stopped the Swing-Johnson Bill to build Boulder Dam to a screeching halt the day before it was to be voted in Congress. Today, studies have pointed out that 2 factors that were undetectable in the 1920s led to the disaster, hydrostatic uplift (Water was seeping under the dam and the weight of the reservoir water was forcing the dam upwards) and the ancient landslide in the area. Although it should be noted that the rock formationshad some tell-tale signs of impending doom.
The St. Francis Dam Disaster is the 2nd worst disaster in California, the 1906 San Francisco Earthquke being the worst, although since the death toll of the St. Francis Dam being inaccurate, and victims being discovered as recent as 1995, there is still the morbid possiblity that the St. Francis is really the worst disaster in California.
Sources
Outland, Charles. Man-Made Disaster: The Story of the St. Francis Dam. Arthur H. Clark: Glendale. 1963