In 1933, the first huge bucketful of wet concrete was poured to begin the building of Boulder Dam (Renamed the Hoover Dam in 1947). Every two-and-a-half minutes, on average, round the clock, another 8-cubic-yard bucketful was added, continuing until the last was placed on 29 May 1933. A system of cableways were strung across the Black Canyon to deliver the loads of material. A cooling system of water pipes was embedded in the structure to carry away the heat of hydration as the concrete cured. The gravity-arch dam was dedicated on 30 Sep 1935 by President Franklin D. Roosevelt. Lake Mead was formed behind it on the Colorado River between Nevada and Arizona.«