Pompeys Pillar

Pompeys Pillar National Monument protects a 150-foot sandstone butte along the Yellowstone River east of Billings in Yellowstone County. The pillar bears the only physical evidence of the Lewis and Clark Expedition still visible at its original site: William Clark's signature carved on July 25, 1806.

The Yellowstone River corridor supports diverse wildlife including white-tailed deer, bald eagles, and various waterfowl. The river provides habitat for sauger, walleye, and paddlefish. Prairie falcons and other raptors nest on the cliff faces.

Ponderosa pine and juniper grow on the butte. Cottonwoods line the nearby Yellowstone River. Native prairie grasses and sagebrush cover the surrounding terrain. Prickly pear cactus grows on the warm, south-facing slopes.

Pompeys Pillar is an erosional remnant of the Rimini Sandstone, a Cretaceous formation. The prominent butte rises 150 feet above the Yellowstone River floodplain. The soft sandstone has preserved carvings and petroglyphs for centuries.

The Yellowstone Valley east of Billings experiences warm, dry summers and cold winters. Annual precipitation averages about 14 inches. The open valley is subject to strong winds.

William Clark named the butte Pompy's Tower after Sacagawea's son, whom he nicknamed Pomp. Clark carved his name and the date on the rock on July 25, 1806. Native peoples used the butte as a landmark for thousands of years, leaving petroglyphs on its surface.

Pompeys Pillar was designated a National Historic Landmark in 1965 and became a National Monument in 2001. The Bureau of Land Management manages the site, which protects Clark's signature behind a protective covering.

Clark's signature is the primary attraction, viewed from a boardwalk on the butte's face. A trail leads to the summit for panoramic Yellowstone Valley views. The interpretive center explains the Lewis and Clark Expedition and earlier Native American use.

The monument offers an interpretive center, boardwalk trail to Clark's signature, summit trail, and picnic facilities. It is located about 28 miles east of Billings off Interstate 94 at exit 23.

Protecting Clark's signature and the surrounding petroglyphs from weathering and vandalism is the primary conservation challenge. A glass and steel covering protects the signature. The soft sandstone requires ongoing monitoring.