Bat Cave mine
 Old cable headhouse at Guano Point, for the aerial tramway to the mine.
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Bat Cave mine site (top center) and old tramway tower.
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"Guano Cafe" at Guano Point.
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The Bat Cave guano mine, located in the western Grand Canyon of Arizona at river mile 266, 800 feet (240 m) above Lake Mead, was an unusual, expensive and noteworthy mining operation. The natural cave was a bat habitat and contained an accumulation of guano.
The cave was apparently discovered in the 1930s by a passing boater. Several unsuccessful early attempts were made to mine the nitrogen-rich guano deposit within the cave for fertilizer. The U.S. Guano Corporation bought the property around 1957. Based on a reputable mining engineer's estimate that the cave contained 100,000 tons of guano, the company constructed an elaborate plan to extract the guano. A small airstrip was built on a nearby sandbar in the Colorado River, and all supplies and machinery needed were then flown in. An aerial tramway was built from the mine to Guano Point on the South Rim, with the cable headhouse built on land leased from the Hualapai tribe. The cableway crossed the river, with a main span of 7,500 feet (2,300 m), and a vertical lift of 2,500 feet (760 m). About 30,000 feet (9,100 m) of 1.5 inch (38 mm) steel cable were used, to support and pull a cable car large enough to transport 2,500 pounds (1,100 kg) of guano. The same car was used to transport the miners to and from work. The guano was mined using a large industrial "vacuum-cleaner" with ten-inch hoses. From the cablehead, the guano was hauled by truck to Kingman, Arizona and packaged for retail sale.
During construction of the cableway, which took 14 months, the first of several mishaps occurred. When first tensioning the main cable, a clutch-lever broke, dropping 9,850 feet (3,000 m) of cable into the canyon. A new cable was ordered and strung, and mining began. The 20,000 feet (6,100 m) pull-cable wore out after a few months use and had to be replaced, bringing the company's total investment up to $US 3,500,000.
The mining engineer's estimate of the potential size of the guano deposit proved wildly optimistic: the cave contained only about 1,000 tons of minable guano, not the 100,000 tons of the engineer's estimate. Most of the cave was filled with valueless limestone rubble.
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Wikipedia