Photographer's notes: "Transmission towers move power lines from the powerhouse of Hoover Dam up out of Black Canyon, Arizona side near the dam, May 21, 2009."

Photographer's notes: "Upstream view of the bridge and dam. The growing arch segments on the Nevada and Arizona sides of the canyon moved toward their rendezvous over the Colorado River." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Aerial view looking down the canyon with the Nevada hairpin turn of the old highway in the foreground." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Ironworkers fabricate rebar forms on the Arizona side, then the forms were transported via highline crane into position for the next segment of arch construction, June 29, 2009." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Aerial view of Lake Mead, Hoover Dam, and the bridge under construction with reflection of the bridge in river below, June 30, 2009." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Aerial view of Lake Mead, Hoover Dam, and the bridge under construction with reflection of the bridge in river below, June 30, 2009." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge

Photographer's notes: "Aerial view looking downstream of the bridge arch construction, the Nevada side hairpin turn of the old road, and the Colorado River, June 30, 2009." Site Name: Mike O'Callaghan-Pat Tillman Memorial Bridge