Photographer's notes: "A high line crane system, which ran between the Arizona and Nevada sides of the canyon, was used to transport materials and workers during the bridge's construction." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Cable stays supported arch construction until the arch was complete. Formwork at the end of the arch segment created the framework for pouring each new concrete section." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "During construction, drivers saw this view as they rounded the Nevada hairpin turn of the old highway. Note: This is one of the few hand held nighttime photographs and the only one taken from a car while in motion. At the time, I did not have permission to stop and photograph from this location." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Ironworkers arrive to work in manbasket, Arizona side of bridge arch construction, Hoover Dam Bypass Project, April 30, 2009." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

This series of photographs documents the historic water overflow at Hoover Dam as seen from the Arizona side of the dam. Taken in August of 1983, this overflow marked the first time the spillways were used during a flood. After initially being filled, the spillways were tested once in August of 1941.

This series of photographs documents the historic water overflow at Hoover Dam as seen from the Arizona side of the dam. Taken in August of 1983, this overflow marked the first time the spillways were used during a flood. After initially being filled, the spillways were tested once in August of 1941.

This series of photographs documents the historic water overflow at Hoover Dam as seen from the Arizona side of the dam. Taken in August of 1983, this overflow marked the first time the spillways were used during a flood. After initially being filled, the spillways were tested once in August of 1941.