Hoover Dam is a concrete arch-gravity dam in Black Canyon on the Colorado River, on the border between Nevada and Arizona. It is a curved wall that holds the water with its weight and its shape.
It stands 726 feet (221 meters) from the rock foundation to the road on the crest. It is the highest of its kind in the United States. It weighs more than 6,600,000 tons.
Construction began in 1931.
Crews work around the clock. They finish the dam two years ahead of schedule.
The mass does not do all the work.
The curve sends the push of the water sideways, into the canyon's rock walls.
What about the heat as the concrete hardens?
More than 650 miles of pipe sit inside the concrete. Cold water runs through them and carries the heat away.
Before the pour, climbers called high scalers hang from ropes at the rim. They climb down cliffs about 656 feet (200 meters) high and knock off loose rock with jackhammers and dynamite.
There is enough concrete to pave a highway from San Francisco to New York.
And more than 6,600,000 tons?
More than a million African elephants.
The desert stays quiet.
The wall holds the river by shape, not by weight alone.
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