William Mulholland (September 11, 1855 – July 22, 1935) was an Irish American self-taught civil engineer who was responsible for building the infrastructure to provide a water supply that allowed Los Angeles to grow into the largest city in California.

In March 1928, Mulholland's career came to an end when the St. Francis Dam failed just over 12 hours after his assistant and he gave it a safety inspection.

In 1874, he disembarked in New York City and headed west to Michigan, where he worked a summer on a Great Lakes freighter and the winter in a lumber camp.

[6] After arriving in Los Angeles, which at the time had a population of about 9,000, Mulholland quickly decided to return to life at sea, as work was hard to find.

In Alta California during the Spanish and Mexican administrations, water was delivered to Pueblo de Los Angeles in a large, open ditch, the Zanja Madre.

[12] Expansion rapidly followed as Mulholland's public-works program began to irrigate large areas of previously arid land.

[14] To create this expansion, Eaton and Mulholland realized that the large amount of runoff from the Sierra Nevada in Owens Valley could be delivered to Los Angeles through a gravity-fed aqueduct.

[17] The 233-mile (375 km)[18] Los Angeles Aqueduct, inaugurated in November 1913, required 3900 workers at its peak[19] and involved the digging of 164 tunnels.

[16]: 74–76 [17]: 152 [22] From a hydrological point of view, the San Fernando Valley was ideal; its aquifer could serve as free water storage without evaporation.

[15]: 92  The historical relationship between water and the rapid urbanization and growth of Los Angeles is the basis for the fictional plot of the 1974 film Chinatown.

[25] The water from Mulholland's aqueduct also shifted farming from wheat to irrigated crops such as corn, beans, squash, and cotton; orchards of apricots, persimmons, and walnuts; and major citrus groves of oranges and lemons.

[26] Mulholland, who was self-taught, became the first American civil engineer to use hydraulic sluicing to build a dam while constructing the Silver Lake Reservoir in 1906.

[28] Government engineers adopted the method when building Gatun Dam, on which Mulholland was a consultant, in the Panama Canal Zone.

The inscription on the diploma read, "Percussit saxa et duxit flumina ad terram sitientum" (He broke the rocks and brought the river to the thirsty land).

[30] That October, with construction of the dam underway, San Francisco's city engineer, Michael O'Shaughnessy, wrote negatively of Mulholland in a letter to John R. Freeman, an engineer who had assisted the city in its pursuit of permission to construct the Hetch Hetchy reservoir and water system in Yosemite National Park.

O'Shaughnessy expressed the view that Mulholland and F. C. Hermann, chief engineer for the SVWC,[31] were "so intensely conceited that they imagine all they might do should be immune from criticism."

Indicating construction details or practices that he thought incorrect, O'Shaughnessy wrote of what was, in his view, sloppiness and recklessness at the Calaveras dam site; he said, "another feature which made objectionable impressions" on him was "the flippant manner in which the young college boys in charge of the work and Mulholland, with his swollen ideas of accomplishment, have undertaken this very serious engineering project.

[33] After the Los Angeles Aqueduct was completed, the San Fernando investors demanded so much water from the Owens Valley that it started to transform from "the Switzerland of California" into a desert.

[16]: 89  By exploiting personal bitterness of some of the Owens Valley farmers, Los Angeles managed to acquire some key water rights.

[16]: 93  Finally, a group of armed ranchers seized the Alabama Gates and dynamited the aqueduct at Jawbone Canyon, letting water return to the Owens River.

The state and local authorities declined to take any action, and the press portrayed the Owens Valley farmers and ranchers as underdogs.

Within seconds after the collapse, only what had been a large section of the central part of the dam remained standing and the reservoir's 12.4 billion gallons (47 million m3) of water began moving down San Francisquito Canyon in a 140-foot-high (43 m) torrent at 18 miles per hour (29 km/h).

The waters traveled south and emptied into the Santa Clara riverbed, flooding parts of present-day Valencia and Newhall.

Following the riverbed, the water continued west, flooding the towns of Castaic Junction, Piru, Fillmore, Bardsdale and Santa Paula in Ventura County.

But the furor that followed upon the mistakes made in the last seven years of his public service discredited the man and thereby gave aid to the enemies of the ideal he had labored all his life to establish.