Bat Cave mine in the western Grand Canyon was the center of a brief guano-mining venture that turned a natural cave into an ambitious industrial operation. After failed efforts in the 1930s, the U.S. Guano Corporation bought the site around 1957, expecting a vast fertilizer deposit. It built an airstrip, an aerial tramway to Guano Point, and vacuum-based extraction equipment, but the engineering feat was undermined by breakdowns and a catastrophic miscalculation: instead of 100,000 tons, only about 1,000 tons of minable guano existed. Mining ended in early 1960 after heavy losses. The site later drew scientific interest and eventually became part of Grand Canyon National Park.