Hoover Dam

Hoover Dam spans the Black Canyon of the Colorado River on the border between Nevada and Arizona, about 50 kilometres southeast of Las Vegas and close to Boulder City. It is owned and run by the US Bureau of Reclamation and forms Lake Mead, the largest reservoir in the United States by capacity when full.

The dam was built between 1931 and 1936 during the Great Depression by thousands of workers, and 96 deaths were officially recorded during construction. President Franklin D. Roosevelt dedicated it on 30 September 1935. It was first called Hoover Dam, then Boulder Dam under the Roosevelt administration, until Congress restored the name Hoover Dam in 1947.

The dam is about 221 metres high and contains about 2.5 million cubic metres of concrete. Its hydroelectric power plant supplies electricity to Nevada, Arizona and California. Art Deco details designed by Gordon Kaufmann, terrazzo floors and the Winged Figures of the Republic sculptures decorate the site.

Visitors can walk across the top of the dam for free. The visitor centre ticket, listed at $15 on the Bureau of Reclamation's 2024 site map, covers the exhibits, the observation deck and the Original Exhibit Building. The guided Dam Tour costs $40 per person (children 3 and under free) and is sold only on site, in person, so arrive early because it sells out; a Powerplant Tour is also offered. Parking in the Nevada-side garage costs $10 per vehicle. The Mike O'Callaghan-Pat Tillman Memorial Bridge, opened in 2010, gives a high view of the dam from a pedestrian walkway. Security checks apply to vehicles approaching the dam.

The shape explains the strength. The dam is about 200 metres thick at its base and narrows to 14 metres at the crest, which runs 379 metres across the canyon. Engineers worked out that a single pour of concrete would take about 125 years to cool, so they built it in column blocks laced with more than 937 kilometres of pipe that carried river water and then refrigerated water through the setting concrete.

The contract went to Six Companies, a joint venture whose bid of $48,890,955 was about $5 million below the next. Seventeen main generators give the power plant a maximum capacity of about 2,080 megawatts; output depends on Lake Mead's level and was 3.3 terawatt-hours in 2020. Look up at the two intake towers: one clock shows Nevada time and the other Arizona time, and because Arizona does not use daylight saving time they agree for more than half the year. Around 7 million people visit the dam each year.