The Mike O'Callaghan – Pat Tillman Memorial Bridge is a dramatic addition to the engineering masterpieces of the American Southwest. Formerly, all of the traffic between Arizona and Las Vegas, Nevada traveled over a narrow road on top of the Hoover dam after winding down a narrow canyon. This dramatic bridge, over a 840 feet above the river, is also a huge tourist attraction and the second highest bridge in the United States. In addition, the bridge cuts almost 45 minutes off of the trip from Phoenix to Las Vegas. Many thousands of vehicles use the bridge every day. The view from the bridge is like flying in an airplane over the dam. Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River. The river is the boundary between Arizona and Nevada so the west side of the dam is in Nevada and the east side of the dam is in Arizona.