In the heart of a geological upthrust, four presidents, memorialized in granite, gaze across the rugged country of South Dakota�s Black Hills. At the foot of the mountain lies Keystone, a small community indelibly linked to the carving of Mount Rushmore. In 1876, prospectors swarmed into the central Black Hills in search of gold. While they did find it, these early miners also found other minerals, such as tin and feldspar. By the turn of the 20th century, Keystone was well-known for its m...