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
Geology of the Grand Canyon area relatively more important than they were before. Steeper cliffs and further widening the Grand Canyon and its tributary canyon system occurred. An average of two debris flows per year reach the Colorado River from tributary canyons to form or expand rapids. This type of mass wasting is the main way the smaller and steeper side canyons transport sediment but it also plays a major role in excavating the larger canyons. In 1963 Glen Canyon Dam and other dams farther upstream started to regulate the flow of the Colorado River through Grand Canyon. Pre-dam but still historic flows of the Colorado