Hoover Dam

When completed in 1935, this immense concrete structure stood as one of the world's greatest engineering feats.

The project began in April 1931, when four tunnels, each 56 feet across, started being hacked out of the canyon walls. Holes were drilled and packed with dynamite, then blasted into oblivion, with thousands of tons of rock loosened, carried off, and dumped, every day for 16 months. Finally, in November 1932, the river water was rerouted around the dam site.

Then came the concrete. For two years, eight-cubic-yard buckets full of cement were lowered into the canyon, five million of them, till the dam - 660 feet thick at the base, 45 feet thick at the crest, 1,244 feet across, and 726 feet high - had swallowed 3.2 million cubic yards of the hard stuff.

The top of the dam was built wide enough to accommodate a two-lane highway. Inside this were placed 17 electric turbines. the cost of the dam surpassed $175 million.

At the peak, over 5,000 workers toiled day and night to complete the project, under the most extreme conditions of heat and dust, and danger from the heavy equipment, explosions, falling rock, heights, etc. (An average 50 injuries a day, and a total of 94 deaths were recorded over the 46 months of construction.)

The largest construction equipment yet known to the world had to be invented, designed, fabricated, and installed on the spot. Yet, miraculously, the dam was completed nearly two years ahead of schedule.