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C': N 00 - - '-. Ware/lOuse Gild machine shop area, Febr/im}' /932. Boulder Ciry is ill background. section and carried it to the penstock header tunnel. and the pipe was then pulled into IX)sition by winches and hoists. Except for the 81/2-foot outlet conduits, which were hot-riveted, and a few miscellaneous sections that were welded, all pipe sectiolls were joined with steel pins, the largest of which were 3 inches in diameter. While the penstock pipes were being installed. placement of concrete for the dam itself was swiftly being carried out. On June 6, 1933, the first bucket of concrete was placed. Six months later one million yards were in place. Another million were placed in the following half year, and the third million by December 6, 1934, only 18 months after the first bucket was poured. 22 The River Harnessed At Last As soon as construction of the dam, in- take towers, and outlet works had been sufficiently completed, and the upstream portions of the two inner diversion tunnels were plugged with concrete, a steel gate was lowered at the outer diversion tunnel inlet on the Arizona side of the river. This was on February I, 1935. Behind the unfinished dam, water started to rise. By midsummer the new reservoir held more than 3 million acre- feet of water and had a maximum depth of 271 feet. The formerly muddy Colorado, dropping its sediment in the reservoir, was transfornled into a lake of clear blue water sparkling in the deselt sun. When the waters of Lake Mead had risen to the base of the intake towers, 260 feet above the riverbed, the one re- maining opening, the outer diversion tun- nel on the Nevada side, was closed. From that time the Colorado had to re- spond to rein. For the first time in history, the Colorado River had been harnessed. Concrete placement continued, and the crest of the dam was reached March 23, 1935. By the following summer all concrete-3,250,335 cubic yards or 6,600,000 tons-was in place. In less than 2 years, 5,000 mcn with new concrete technology had built a structure greater in volume than the largest pyramid in Egypt, a structure which, according to Herodotus, required 100,000 men working 20 years to complete. The dam towers 726.4 feet above bedrock, a distance equivalent to the height of a 60-story skyscraper. It has a base thickness of 660 feet, or the length of two ordinary residential blocks; is 45 feet thick at the crest; and stretches 1,244 feet or nearly a quarter of a mile between the Nevada and Arizona walls