Hoover Dam Facts

The floor of Hoover Dam's monument plaza is a celestial map. Sculptor Oskar J.W. Hansen embedded 209 brass discs into the terrazzo, each marking a star or planet visible on September 30, 1935 - the night FDR dedicated the dam. It took 200,000 astronomical calculations. If every historical record vanished, a future civilization could read that floor and calculate exactly when Hoover Dam was dedicated.

Hoover Dam's spillway tunnel tore itself open in 1941. After a gate dropped without warning, water roaring down the Arizona spillway gouged a hole about 115 feet long, 30 feet wide and 45 feet deep, through the concrete and into the rock. The 1983 flood damaged the tunnels again. Today Lake Mead sits so low that the dam's two spillways stand bone dry, about 165 feet above the water.