Pompey's Pillar was discovered and named by Captain William Clark of the Lewis and Clark Expedition on July 25, 1806. Returning down the Yellowstone with Clark were Pryor, Shannon, Bratton, Windsor, Hall, Shields, Gibson, Labiche, Chaboneau, Sacajawea and child, and York the slave. The place is associated with gratitude to Lewis and Clark as intrepid leaders, to Sacajawea as their unerring guide, and to the fidelity and courage of all the company.