On July 25, 1806, Captain William Clark of the Lewis and Clark Expedition stopped here and carved his name and the date into the rock. His inscription is the only evidence still visible along the trail to mark the Corps of Discovery's historic journey. Clark was not the first or the last to be drawn to this geological formation. He wrote in his journal, "The nativs have ingraved on the face of this rock the figures of animals &c. near which I marked my name and the date of the month & year." The Plains tribes still treat the Pillar as a sacred site. The Pillar contains hundreds more historical markings left by early American fur trappers, explorers, homesteaders, and others in the 19th and 20th centuries, who, like Clark, admired this "remarkable rock."