Boulder Canyon, once called Devils Gate Canyon, was a Colorado River canyon between Nevada and Arizona above Hoover Dam. Now largely submerged beneath Lake Mead, it formerly marked a natural break in the Black Mountains and divided the Arizona and Nevada ranges. The canyon also figured in the river’s steamboat era: from 1879 to 1887, salt mined along the Virgin River was hauled by leased steamboats downriver to Eldorado Canyon. In April 1883, Captain John Alexander Mellon placed six heavy iron ring bolts in the canyon so lines could steady steamboats through its dangerous rapids during high-water trips toward Rioville.