Boulder Canyon (Colorado River) steamboats as they passed over the dangerous rapids of Devil's Gate Canyon, during their high water runs to the mouth of the Virgin River at Rioville, Nevada. Boulder Canyon (Colorado River) Boulder Canyon, originally Devils Gate Canyon, is a canyon on the Colorado River, above Hoover Dam, now flooded by Lake Mead. It lies between Clark County, Nevada and Mohave County, Arizona. It heads at western end of the Virgin River Basin of Lake Mead, at about . Boulder Canyon divides the Black Mountains into the Black Mountains of Arizona, and the Black Mountains of Nevada. Its mouth is now
Steamboats of the Colorado River Colorado route, and was the model for all the steamboats on the river thereafter. From 1859, prospectors dispersed up the Colorado River valley in the next few years, finding gold deposits along the river as far as the Black Canyon. In 1860, gold was found across the Colorado River from Potholes in Arizona, in placers at La Laguna. The strikes that followed in the next four years would make George A. Johnson and his two partners wealthy. By March 1861, the secession crisis had led to the closing of the Butterfield Overland Mail. February 19, 1861, the Bascom Affair led