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 the river, except for the "Searchlight" that lingered on as property of the U. S. Reclamation Service until it was sunk in 1916. Steamboats were tried in Glen Canyon, the Green River in Utah and Wyoming and the Grand River, (after 1921 renamed as the upper part of the Colorado River), above its confluence with the Green River in Utah and in Colorado. Unlike the Lower Colorado, the railroads made possible most of this steam navigation on the Upper Colorado, bringing in the boats or their parts and their fuel to the points on the river where they were assembled