U.S. Route 93 in Nevada portion of abandoned railroad right-of-way. A shopping center now sits where the original truck bypass alignment once ran. US 93 was realigned again on October 19, 2010, when the Mike O'Callaghan – Pat Tillman Memorial Bridge over the Black Canyon of the Colorado River opened to vehicular traffic. With that, the highway no longer passes over Hoover Dam, and the state-maintained portion of the replaced route was renamed as Hoover Dam Access Road (SR 172). In 2011, US 93 from Buchanan Boulevard to the Nevada terminus of the Hoover Dam Bypass was expanded to four through lanes with dedicated turn
Colorado River beyond Yuma, Arizona, and the confluence with the intermittent Gila River – which carries runoff from western New Mexico and most of Arizona – before defining about of the Mexico–United States border. At Morelos Dam, the entire remaining flow of the Colorado is diverted to irrigate the Mexicali Valley, among Mexico's most fertile agricultural lands. Below San Luis Río Colorado, the Colorado passes entirely into Mexico, defining the Baja California–Sonora border; in most years, the stretch of the Colorado between here and the Gulf of California is dry or a trickle formed by irrigation return flows. The Hardy River provides