These two air compressors were typical of those used in hard-rock mining. The Gardner-Denver air compressor, powered by a gasoline engine, was a mobile type moved wherever it was needed, while the Ingersoll-Rand air compressor, powered by an electric motor, was a stationary type usually mounted on a concrete slab. They provided high-pressure air mostly to drive percussive rotary rock drills used to drill holes for explosives, with holes usually 1 ¾ inches in diameter and 6 to 12 feet deep. Rock drills were used both on the surface in open cuts and underground in tunnels. Compressed air also ran air motors for various types of equipment in underground spaces where fumes from fuel-driven engines would be dangerous and where electricity was not available or as convenient to use. These compressors were used in the Guadalupe mine from the 1940s until the mine closed in the 1970s, and the Guadalupe Rubbish Company donated them to NAQCPA in 1987.