After a catastrophic breach that caused the Colorado River to fill the Salton Sea,[9] the Southern Pacific Railroad spent $3 million in 1906–07 to stabilize the waterway, an amount it hoped in vain that it would be reimbursed for by the federal government.

Service chief Arthur Powell Davis proposed using dynamite to collapse the walls of Boulder Canyon,[12] 20 miles (32 km) north of the eventual dam site, into the river.

In 1922, after considering it for several years, the Reclamation Service finally rejected the proposal, citing doubts about the unproven technique and questions as to whether it would, in fact, save money.

[19] Initial talks produced no result, but when the Supreme Court handed down the Wyoming v. Colorado decision undermining the claims of the upstream states, they became anxious to reach an agreement.

They lacked sufficient resources even in combination with their longtime partners, Morrison-Knudsen, which employed the nation's leading dam builder, Frank Crowe.

[31] The city of Las Vegas had lobbied hard to be the headquarters for the dam construction, closing its many speakeasies when the decision maker, Secretary of the Interior Ray Wilbur, came to town.

To meet the deadline, Six Companies had to complete work by early 1933, since only in late fall and winter was the water level in the river low enough to safely divert.

[52] The inner diversion tunnels were plugged at approximately one-third of their length, beyond which they now carry steel pipes connecting the intake towers to the power plant and outlet works.

[55] The cofferdams were designed to protect against the possibility of the river's flooding a site at which two thousand men might be at work, and their specifications were covered in the bid documents in nearly as much detail as the dam itself.

The high scalers received considerable media attention, with one worker dubbed the "Human Pendulum" for swinging co-workers (and, at other times, cases of dynamite) across the canyon.

As the required grade of aggregate in the concrete differed depending on placement in the dam (from pea-sized gravel to 9 inches [230 mm] stones), it was vital that the bucket be maneuvered to the proper column.

Although there are myths that men were caught in the pour and are entombed in the dam to this day, each bucket deepened the concrete in a form by only 1 inch (25 mm), and Six Companies engineers would not have permitted a flaw caused by the presence of a human body.

[68] With most work finished on the dam itself (the powerhouse remained uncompleted), a formal dedication ceremony was arranged for September 30, 1935, to coincide with a western tour being made by President Franklin D. Roosevelt.

Workers alleged that this diagnosis was a cover for death from carbon monoxide poisoning (brought on by the use of gasoline-fueled vehicles in the diversion tunnels), and a classification used by Six Companies to avoid paying compensation claims.

[85] With the assistance of the National Laboratory of Anthropology, True researched authentic decorative motifs from Indian sand paintings, textiles, baskets and ceramics.

[86] The images and colors are based on Native American visions of rain, lightning, water, clouds, and local animals—lizards, serpents, birds—and on the Southwestern landscape of stepped mesas.

[84] In these works, which are integrated into the walkways and interior halls of the dam, True also reflected on the machinery of the operation, making the symbolic patterns appear both ancient and modern.

[88] True's consulting artist job lasted through 1942; it was extended so he could complete design work for the Parker, Shasta and Grand Coulee dams and power plants.

True's work on the Hoover Dam was humorously referred to in a poem published in The New Yorker, part of which read, "lose the spark, and justify the dream; but also worthy of remark will be the color scheme".

In his words, Hansen wanted his work to express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment", because "[t]he building of Hoover Dam belongs to the sagas of the daring.

[91] Hansen's bas-relief on the Nevada elevator tower depicts the benefits of the dam: flood control, navigation, irrigation, water storage, and power.

[95] In the latter half of 1936, water levels in Lake Mead were high enough to permit power generation, and the first three Allis Chalmers built Francis turbine-generators, all on the Nevada side, began operating.

The Colorado River Aqueduct and Central Arizona Project branch off Lake Havasu while the All-American Canal is supplied by the Imperial Dam.

In total, water from Lake Mead serves 18 million people in Arizona, Nevada, and California and supplies the irrigation of over 1,000,000 acres (400,000 ha) of land.

[111][112] The powerhouse was run under the original authorization by the Los Angeles Department of Water and Power and Southern California Edison; in 1987, the Bureau of Reclamation assumed control.

[113] In 2011, Congress enacted legislation extending the current contracts until 2067, after setting aside 5% of Hoover Dam's power for sale to Native American tribes, electric cooperatives, and other entities.

This complex spillway entrance arrangement combined with the approximate 700-foot (210 m) elevation drop from the top of the reservoir to the river below was a difficult engineering problem and posed numerous design challenges.

[115] The 1941 damage was attributed to a slight misalignment of the tunnel invert (or base), which caused cavitation, a phenomenon in fast-flowing liquids in which vapor bubbles collapse with explosive force.

[120] Hoover Dam opened for tours in 1937 after its completion but following Japan's attack on Pearl Harbor on December 7, 1941, it was closed to the public when the United States entered World War II, during which only authorized traffic, in convoys, was permitted.

[133] The official status this conferred to the name "Hoover Dam" had been noted on the floor of the House of Representatives by Congressman Edward T. Taylor of Colorado on December 12, 1930,[134] but was likewise ignored by Ickes.