During the 1930's, a boater passing through the Canyon discovered a cave later found to be rich with guano, or bat droppings, a nitrogen-rich material useful as fertilizer. The U.S. Guano Corporation purchased the mining rights in 1957 and began constructing a tramway to extract guano from the mine. Using cable spanning the Canyon at 7,500 feet and cable cars for both the guano and the miners, the site was mined until early 1960. A few months later, an Air Force jet's tail damaged the cable, and the operation never reopened. The cable head-house remains, along with some remnants at the cave, and the site is now a tourist destination at Grand Canyon West.