Mount Rushmore National Memorial is a massive sculpture carved into the granite face of Mount Rushmore in the Black Hills of South Dakota. Sculpted by Gutzon Borglum and his son Lincoln, the project lasted from 1927 to 1941. It features the 60-foot-tall heads of four U.S. presidents: George Washington (representing birth), Thomas Jefferson (growth), Theodore Roosevelt (development), and Abraham Lincoln (preservation). Roughly 90% of the mountain was removed using dynamite, with the remaining few inches carved by 'honeycombers' using jackhammers and chisels. There is a hidden chamber behind Abraham Lincoln's head called the 'Hall of Records,' intended to store the nation's most important documents. The site remains controversial as it was carved into land sacred to the Lakota Sioux, who refer to the mountain as 'The Six Grandfathers.'