Step 1 : Introduction to the question "What was used to carve 90% of Mount Rushmore?"
...Creating a certain mountainside portrait of four presidents took the work of 400 men and women — and a whole lot of dynamite. The dangerous explosive was responsible for 90% of the carving done on Mount Rushmore, with charges used in a surprisingly precise manner until three to six inches of rock were left. From there, holes were drilled in a process called honeycombing until the last bit of granite could be removed by hand. If that sounds arduous, that's because it was — altogether, the memorial took 14 years of work. Completed in 1941, Mount Rushmore is truly more than meets the eye.