Pompeys Pillar National Monument, located along the Yellowstone River approximately 28 miles east of Billings in south-central Montana, preserves a 150-foot sandstone butte that holds one of the most significant physical artifacts of the Lewis and Clark Expedition of 1804–1806. On July 25, 1806, during the return leg of the Corps of Discovery's journey, Captain William Clark carved his name and the date into the sandstone surface of the formation, creating the only surviving in-situ physical evidence of the expedition's passage across the landscape. The inscription—"Wm Clark July 25 1806"—is clearly legible today and protected beneath a glass enclosure.
Clark named the formation Pompys Tower after Jean Baptiste Charbonneau, the infant son of Sacagawea and Toussaint Charbonneau who traveled with the Corps. Later cartographers altered the spelling to Pompeys Pillar. The butte is a remnant of the ancient Yellowstone River floodplain, composed of Judith River Formation sandstone, and rises dramatically from the valley floor, offering panoramic views of the river corridor and surrounding plains.
A 0.4-mile boardwalk trail ascends from the visitor center to the summit plateau, passing interpretive panels documenting the Clark inscription, Indigenous rock art (pictographs and petroglyphs) made by Native peoples over thousands of years before Clark's visit, and geological formations along the rock face. The visitor center at the base contains exhibits about the Corps of Discovery, the Crow Nation who inhabited the region, and the natural history of the Yellowstone River Valley. The monument is managed by the Bureau of Land Management and is open seasonally from May through September. Situated just off Interstate 94, it is a manageable day trip from Billings and a key stop along the Lewis and Clark National Historic Trail.
Why it matters
Pompeys Pillar preserves the only in-situ physical signature of the Lewis and Clark Expedition—William Clark's carved inscription of July 25, 1806—making it the most tangible surviving remnant of the Corps of Discovery's transcontinental journey through the American West.
Location
Pompeys Pillar Rd, Pompeys Pillar, MT 59064
45.9980, -107.9571 View on map
Highlights
- William Clark's 1806 hand-carved inscription—the only surviving in-situ physical evidence of the Lewis and Clark Expedition
- Ancient Native American pictographs and petroglyphs on the sandstone butte face
- Panoramic summit views of the Yellowstone River valley from 150 feet above the valley floor
- Interpretive boardwalk trail documenting the Corps of Discovery's 1806 return journey
- Visitor center exhibits covering the Crow Nation, Lewis and Clark, and regional geology
Tips for visiting
- Visit in the morning when the Clark inscription is in shadow and most legible—afternoon sun can wash out the carved surface
- The boardwalk trail is 0.4 miles round trip and involves a steep climb to the summit platform
- The monument is open May through September only—confirm the visitor center hours before making the drive
- Binoculars help when examining pictographs positioned higher on the cliff face
- Combine the visit with a stop at the adjacent Pompeys Pillar Recreation Area along the Yellowstone River for fishing or picnicking
Frequently asked questions
How long does a typical visit take?
Most visitors spend 1–1.5 hours: approximately 30 minutes in the visitor center and 45 minutes on the boardwalk trail to the summit and back.
Is the site accessible for visitors with mobility limitations?
The visitor center is fully accessible. The boardwalk trail to the summit includes stairs and steeply inclined sections, making the area around the Clark inscription difficult to reach for visitors with limited mobility. Staff at the visitor center can advise on alternatives.
Is the site appropriate for children?
Yes. The trail is short and manageable for school-age children, and the Clark inscription and Indigenous rock art are engaging historical touchpoints for young visitors.