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
Black Canyon Diversion Dam by the Bureau. The riverine reservoir it creates, the Black Canyon Reservoir, has a normal water surface of 1.7 square miles, about twelve miles of shoreline, and an original maximum capacity of 44,700 acre-feet, reduced by siltation to about 31,200 acre-feet. Recreation includes boating and fishing. The installation of a third hydropower generating unit has been funded by Bonneville Power Administration for completion in 2013. Black Canyon Diversion Dam Black Canyon Diversion Dam (National ID # ID00282) is a dam in Gem County, Idaho. The concrete dam was originally completed in 1924, then re-constructed between 1951 and 1955, by the