Bat Cave mine

mining engineer's estimate that the cave contained 100,000 tons of guano, the company constructed an elaborate plan to extract it. A small airstrip was built on a nearby sandbar in the Colorado River, and all supplies and machinery needed were 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 Native American 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

Tadarida brasiliensis, which eat insects. Martin collected a sample from 7 ft (2m) below the surface of the guano, which yielded a radiocarbon date of 12,900 ± 1,500 years ago. The miners reported finding "bat graveyards," some with mummified free-tail bats. No giant meat-eating bats were discovered. Martin had hoped to find fossil pollen, his research interest at that time, but found none in his samples. ^[2]

US Air Force jet, illegally "hot-dogging" down the canyon, clipped the cable, damaging the plane's wing and severing the cable. The plane survived, and U.S. Guano successfully sued the Air Force for damaging their property, offsetting some of their losses.^{[citation needed}