Pompeys Pillar is one of the most famous sandstone buttes in America. It bears the only remaining physical evidence of the Lewis and Clark Expedition, which appears on the trail today as it did 200 years ago. On the face of the 150-foot butte, Captain William Clark carved his name on July 25, 1806, during his return to the United States through the beautiful Yellowstone Valley. [From pompeyspillar.org]