More than 450,000 tons of rock were removed from Mount Rushmore to bring out the four presidential faces. About 90% of the rock was removed with dynamite, and the rest was removed by drilling with jackhammers and wedging rock off the mountain, with final finishing work completed using small jackhammers and facing bits. Air compressors at the base of the mountain powered the jackhammers, including the Ingersoll-Rand Imperial Type 10 Air Compressor, the largest of three operating in the compressor house at this site during the carving. For much of the carving period, Keystone Consolidated Mines supplied the electrical power for these compressors. An 1,800-foot, 3-inch pipeline ran up the mountain along the stairway to carry air from the compressor below to the jackhammers, and in cold weather a liquid gas was injected as a fine mist into the pipeline beyond the compressors to prevent freezing. The pipeline was later enlarged and expanded to supply compressed air to more jackhammers. In 1936, National Park Service engineer Julian Spotts checked the system for leaks and found that a blacksmith had tapped into the line with a nozzle to blow compressed air on himself while he worked, so Spotts provided a fan instead. Spotts also investigated a large power loss that occurred every Monday morning and found that many women in Keystone were using electric washing machines for laundry, so he asked the Mount Rushmore Commission to buy a gasoline-powered auxiliary compressor, after which the power problems ended. These improvements increased the minimum number of jackhammers that could be operated from 16 to 22. Black Hills Power and Light completed a power line to Rushmore in 1939, providing all the electricity needed for the remaining two years of carving work. Today, this compressor and sections of pipe still in place on Mount Rushmore testify to the power required to carve the mountain.

Photo: Barry Swackhamer

Keystone, South Dakota · USA