Course of the Colorado River into the Virgin River, which ran southward through what is now Overton Arm to join the Colorado River near the now-ghost town of St. Thomas, Nevada. At Hoover Dam, the Colorado turns due south through Black Canyon, a direction it will follow for the remainder of its course to the Gulf of California. It passes under the Mike O'Callaghan–Pat Tillman Memorial Bridge (Hoover Dam Bypass), the highest concrete arch bridge in the world, carrying U.S. Route 93 at a height of above the Colorado River. At the end of Black Canyon the Colorado widens into Lake Mohave, created by the
Cottonwood Valley (Arizona and Nevada) Cottonwood Valley (Arizona and Nevada) Cottonwood Valley is a wide valley, on the Colorado River on the border between Mohave County, Arizona and Clark County, Nevada. It extends east and west from the river into both states and is the first wide valley south of the Black Canyon of the Colorado, the last in a series of great canyons the Colorado River passes through after leaving the Rocky Mountains on its way west and where it makes its turn to the south toward the Gulf of California. All of the Colorado River in Cottonwood Valley and the lower reach of