National Register Listing

Hoover Dam

a.k.a. Boulder Dam

E of Las Vegas on U.S. 93, Boulder City, NV

Hoover Dam is among the largest and earliest of the Bureau of Reclamation's massive multiple-purpose dams. By providing electric power, flood control, and irrigation waters, the dam made increased levels of population and agricultural production in large areas of the Southwest feasible, affecting not only lands near the river, but also urban centers such as Los Angeles. Hoover Dam was not the first major arch-gravity dam to be constructed. The Cheesman Dam in Denver, for example, predates it. Nor is the dam the first of the Bureau of Reclamation's multi-purpose dams in the United States; that distinction belongs to the Theodore Roosevelt Dam, already a National Historic Landmark. Hoover Dam is, however, distinguished by its size, the size of its hydroelectric plant, and the far-reaching consequences of its construction in the agricultural, industrial, and urban development of the Southwestern United States.

In the field of hydraulic engineering, the dam is an accomplishment comparable to the Panama Canal. Hoover Dam was the highest dam in the world-- 726.4 feet from bedrock to the crest-- when it was constructed. Today it is still the western hemisphere's highest concrete dam. Because of this height, it created a reservoir that could store the normal flow of the river, including all average floods, for 2 years. When filled to the maximum, it will impound more than 31 million acre-feet of water. The dam is also large enough to trap and hold the millions of tons of sediment carried by the river every year, without seriously impairing its efficiency as a reservoir or interfering with the generation of electrical power.

One of the major engineering techniques developed in the construction of Hoover Dam was the cooling of the concrete. If the dam had been allowed to cool naturally, it would have taken more than a century to do so, and it would have shrunk and cracked as it cooled. Engineers solved this problem by building the dam in pier-like blocks and cooling the concrete by running ice-cold water through more than 582 miles of pipe embedded in the blocks. This permitted dissipation of the chemical heat generated by the "setting up" of the concrete and the cooling was completed in March 1935.

Hoover Dam's role in the history of hydroelectric power is indicated by the fact that from 1939 until 1949, the dam's powerplant was the largest hydroelectric powerplant in the world. It provides electrical energy for transmission to southern California, southern Nevada, and parts of Arizona, contributing to industrial and population growth in those areas. Directly or through interconnections, the Hoover powerplant has facilitated mining and minerals exploitation projects in California, Nevada, and Arizona.

Local significance of the structure:
Listed in National Register of Historic Places in 1981.