Mount Rushmore community. Recent pine beetle infestations have threatened the forest. Mount Rushmore is largely composed of granite. The memorial is carved on the northwest margin of the Black Elk Peak granite batholith in the Black Hills of South Dakota, so the geologic formations of the heart of the Black Hills region are also evident at Mount Rushmore. The batholith magma intruded into the pre-existing mica schist rocks during the Proterozoic, 1.6 billion years ago. Coarse grained pegmatite dikes are associated with the granite intrusion of Black Elk Peak and are visibly lighter in color, thus explaining the light-colored streaks on the
Mount Rushmore 31, 1941, Gutzon Borglum and 400 workers sculpted the colossal 60 foot (18 m) high carvings of U.S. presidents George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln to represent the first 130 years of American history. These presidents were selected by Borglum because of their role in preserving the Republic and expanding its territory. The carving of Mount Rushmore involved the use of dynamite, followed by the process of "honeycombing", a process where workers drill holes close together, allowing small pieces to be removed by hand. In total, about of rock were blasted off the mountainside. The image of