Pompeys Pillar: Clark's Name in Stone

About twenty-five miles east of Billings, the Yellowstone River bends around a sandstone butte that rises about one hundred fifty feet above the valley floor. On July twenty-fifth, eighteen oh six, William Clark climbed it. He carved his name and the date into the soft rock near the top, and that inscription is the only surviving physical evidence anywhere along the entire Lewis and Clark route that was left by the expedition and can be indisputably linked to them. Everything else they touched has vanished or decayed. This one carving remains.

Clark had named the formation Pompy's Tower, after a toddler he had grown genuinely fond of, Jean Baptiste Charbonneau, the infant son of Sacagawea and Toussaint Charbonneau, who had ridden on his mother's back across the continent. Clark's nickname for the boy was Pomp. In a letter to the boy's father, Clark wrote that he wanted to raise the child as his own. When the account of the expedition was published in eighteen fourteen, an editor changed the name to Pompey's Pillar, and that name stuck.

The rock itself is Upper Cretaceous sandstone, roughly seventy million years old, formed from the sediments of an ancient inland sea. The Apsaalooke, the Crow people, knew this stretch of the Yellowstone well long before Clark arrived. The pillar would have been a landmark to anyone moving through the valley, visible from a distance, distinctive, a reference point in flat country.

Clark's signature is now protected behind a glass panel. Visitors can still climb to the top on a boardwalk, and from that height you can see roughly the same view Clark recorded in his journal on that July morning more than two centuries ago.