A soaring bridge that will let drivers bypass the Hoover Dam - and steer clear of its security checkpoints and tourists - will open after nearly eight years and £151 million worth of work.
The 1,900ft engineering wonder perched 890ft above the Colorado River is expected to slash travel time along the main route between Las Vegas, Nevada, and Phoenix, Arizona, as motorists will no longer have to make their way across the dam's winding two-lane road at a snail's pace.
US transportation secretary Ray LaHood and a delegation of government officials including Arizona governor Jan Brewer and US Senate majority leader Harry Reid of Nevada, hailed the span linking the states as a crucial example of work being done nationwide to update America's infrastructure.
Mr LaHood said the bypass was one of 15,000 transportation projects that included updating 4,000 miles of road.
The bridge, which officially opens next week, is named after former Nevada governor Mike O'Callaghan and Pat Tillman, the former National Football League player who quit the Arizona Cardinals to join the Army Rangers and died under friendly fire in Afghanistan.
Family members of Mr O'Callaghan and Mr Tillman watched the dedication ceremony from the span along with hundreds of building workers and their families.
People took photographs and walked along the bridge before the ceremony, many taking long pauses to stare at the 75-year-old dam below - itself regarded as an engineering marvel.
It took five years and 21,000 workers to build the dam, and it cost £104 million. The last of its more than five million barrels of cement was poured in 1935.
The bridge contains 16 million pounds of steel, 30,000 cubic yards of concrete and two million feet of cable - enough to stretch well past Phoenix from Las Vegas. The £151 million price tag includes the cost to build roads and smaller bridges leading to the picturesque span.
The bridge is the longest built with concrete arches in the western hemisphere, according to the Transportation Department. The arches measure 1,060ft.