Pausing at Traveler's Rest from June 30 to July 3, 1806, Lewis and Clark decided that it would be best to divide the group into separate parties, maximizing their exploratory range. Clark and his party traversed Bozeman Pass, set out down the Yellowstone River, and headed for the caches at Beaverhead. Along the way, the crew came across a prominent rock formation, located on the south bank of the river in present-day Nibbe, Montana. Naming the anomalous natural formation after Sacagawea's child Jean Baptiste Charbonneau or 'Pomp', Clark wrote of the discovery in his journal that evening:

William Clark's signature, dated July 25, 1806 Photo from Bureau of Land Management

. . . At 4PM [I] arrived at the remarkable rock situated in an extensive bottom.This rock I ascended and from it's top had a most extensive view in every direction. This rock which I shall call Pompy's Tower is 200 feet high and 400 paces in secumpherance and only axcessible on one side which is from the N.E. the other parts of it being a perpendicular clift of lightish coloured gritty rock.The Indians have made 2 piles of stone on the top of this tower. The nativs have ingraved on the face of this rock the figures of animals &c.(Jones 2000, 185-186)

Clark, too, left his mark at Pompey's Pillar, engraving his name and the date into the stone; still visible, his mark is probably the only extant on-site evidence of the entire expedition.

Pompey's Pillar National Monument, a National Historic Landmark, is managed by the Bureau of Land Management, U.S. Department of the Interior. The Pillar overlooks the Yellowstone River about 25 miles east of Billings, Montana. From Memorial Day weekend through Labor Day the National Monument is open to drive-in visitation from 8:00am to 8:00pm; after Labor Day through the remainder of September the hours are 9:00am to 5:00pm; from October to the Memorial Day weekend, vehicle gates are closed, but the Monument is open to walk-in visitors although no services are available. Please call 406-875-2233, or visit the monument's website for further information. You can also download (in pdf) the Pompey's Pillar National Historic Landmark nomination.