The era of these megastructures began during the 1930s with the construction of the Hoover Dam on the Colorado River and the Grand Coulee Dam on the Columbia River. The vertiginous Hoover Dam, located in a gorge southeast of Las Vegas, required about 3.4 million cubic meters of concrete and 20,000 tons of reinforcing steel, twice as much plate and pipe steel, and 8,000 tons of structural steel.[96]
