Pompeys Pillar National Monument

Pompeys Pillar National Monument, on the Yellowstone River about 28 miles east of Billings in south-central Montana, preserves one of the most historically significant landmarks in the American West — a 150-foot sandstone butte on the Yellowstone River where William Clark carved his name and the date (July 25, 1806) during the return journey of the Lewis and Clark Expedition, leaving the only known physical, on-site evidence of the Corps of Discovery remaining in the American landscape.

Clark named the butte “Pompeys Tower” for Sacagawea’s infant son, Jean Baptiste Charbonneau (nicknamed “Pomp” — later to become one of the most remarkable figures of the early American West in his own right). The pillar also bears Native American pictographs and petroglyphs, including ancient rock art predating Clark’s signature. The butte summit provides a panoramic view of the Yellowstone River valley that Clark himself described in his journal. Pompeys Pillar is a treasured Lewis and Clark landmark and geological icon of eastern Montana.

May through September is the monument’s primary visitor season — the visitor center and boardwalk trail are fully operational, and the Yellowstone River corridor is green and wildlife-rich. July 25 (the anniversary of Clark’s 1806 inscription) is the monument’s most meaningful date; BLM sometimes holds special anniversary programs. Spring (April-May) is excellent for the Yellowstone riparian birding and for the monument’s wildflowers on the butte face. Summer (June through August) is the peak season with the longest days and warmest temperatures for the summit view. The monument is accessible year-round (the boardwalk is open when not icy), but the visitor center is seasonal. Summer for the full visitor center experience and the summit view, and late April or May for the riparian birding are the recommendations.

On July 25, 1806, Captain William Clark — returning from the Pacific with the Corps of Discovery on a separate route from Meriwether Lewis — climbed a sandstone butte on the Yellowstone River and carved his name and the date into the soft rock, naming the butte “Pompeys Tower” for Sacagawea’s infant son Jean Baptiste Charbonneau (nicknamed “Pomp” by Clark, who was devoted to the child). Clark’s inscription — still legible on the sandstone 220 years later — is the only known physical on-site evidence of the Lewis and Clark Expedition remaining in the American landscape. Jean Baptiste Charbonneau grew up to become one of the most remarkable figures of the early American West: educated in Europe, fluent in multiple languages, and a guide and frontiersman in the American Southwest. The butte was also known to the Crow people and earlier peoples — the Native American rock art on the butte face predates Clark’s inscription by centuries. The monument was established in 1965 and transferred to BLM management.

Pompeys Pillar is an erosional remnant of the Cretaceous Eagle Creek Sandstone — the same white to cream-colored marine sandstone that forms the dramatic cliff faces of the Missouri River Breaks to the north and the Bighorn Canyon walls to the south. The Eagle Creek Sandstone (Campanian, approximately 75-80 million years old) is a soft, well-cemented sandstone that resists erosion better than the surrounding mudstones, creating isolated buttes and rimrock formations across eastern Montana as the softer rocks erode away. Pompeys Pillar is a classic “butte” landform — a flat-topped, steep-sided erosional remnant isolated from the surrounding rimrock by lateral erosion. The Yellowstone River has been an important factor in the pillar’s isolation, undercutting the softer mudstones on its south side. The Eagle Creek Sandstone, the differential erosion of the surrounding mudstones, and the Yellowstone River’s lateral erosion created Pompeys Pillar.

Pompeys Pillar NM’s Yellowstone River corridor supports a diverse riparian and grassland wildlife community — white-tailed deer (in the cottonwood riparian forest along the river), mule deer (on the drier slopes above the pillar), Canada geese and mallards (on the Yellowstone), common mergansers (fishing the river), belted kingfishers, great blue herons, osprey (fishing the river in summer — a nest is sometimes present in the large cottonwoods near the pillar), least terns and piping plovers (Montana-sensitive shorebirds that nest on Yellowstone River sandbars near the monument in summer), and a rich riparian songbird community (yellow warbler, common yellowthroat, spotted towhee, bullock’s oriole) in the cottonwood corridor. The river-corridor wildlife and the osprey are the standout wildlife encounters.

Pompeys Pillar NM preserves a small but ecologically significant section of the Yellowstone River riparian corridor — one of the longest free-flowing rivers in the United States, supporting a native cottonwood forest ecosystem that has been largely degraded by agriculture, development and invasive species in the surrounding Yellowstone valley. The monument’s cottonwood riparian forest provides critical nesting and stopover habitat for migratory songbirds. The native sandbar habitats on the Yellowstone (adjacent to the monument) support state-sensitive breeding populations of least terns and piping plovers — two shorebird species dependent on undisturbed sand-and-gravel river islands. Invasive tamarisk management is an ongoing conservation challenge in the Yellowstone riparian corridor. The monument’s small size (512 acres) belies its ecological and historical significance.

Pompeys Pillar National Monument holds an irreplaceable place in the heritage of the American West — as the single location where a physical artifact of the Lewis and Clark Expedition (Clark’s carved signature, still readable 220 years later) can be seen in its original context, in the landscape where it was made, on the same butte where Clark stood and looked out over the Yellowstone River valley. The monument also honors Jean Baptiste Charbonneau, the child of Sacagawea for whom the pillar was named, and preserves Native American rock art on the same sandstone face. For any traveler interested in the Lewis and Clark Expedition, Pompeys Pillar is one of the most moving and authentic Lewis and Clark sites in the country — a place where the history is not in a museum but written in the rock itself. Pompeys Pillar is a cherished historical and geological icon of Montana.

Pompeys Pillar National Monument is on MT-312, approximately 28 miles east of Billings (take I-90 east from Billings to exit 23, then follow MT-312 north for 1 mile to the monument entrance). Billings (the largest city in Montana, 28 miles west) has full resort services. A BLM day-use entrance fee applies (America the Beautiful Pass accepted). The monument is open daily; the visitor center is open May through September (check BLM for current hours). The boardwalk trail to the summit and Clark’s signature is open year-round when not icy (it is accessible in winter if conditions allow). The monument has no campground (camping is available at Pompeys Pillar Campground, a private campground adjacent to the monument, and at BLM campgrounds east of Billings). Check BLM for current hours and conditions before visiting.

The Bureau of Land Management manages Pompeys Pillar NM. Clark’s signature is the monument’s most critical conservation feature — it is protected under a glass cover to prevent vandalism and weathering, and visitors view it from the boardwalk without physical contact. Never touch any rock art or historical inscription (the oils in fingerprints accelerate sandstone weathering and rock art deterioration). The Native American petroglyph panels on the butte face are equally protected — do not touch, trace or photograph with flash. Stay on the boardwalk trail on the butte face; do not leave the trail or attempt to access any part of the butte face without the boardwalk. Report any vandalism or new graffiti to BLM immediately. Support the BLM’s Pompeys Pillar preservation program.

The boardwalk trail to the summit involves steep sections and exposed cliff-edge walkways with railings — hold the railing at all times and do not allow children to run on the boardwalk (the exposed butte-face sections have significant drops below). The summit is unprotected at the very top; maintain safe distances from the edge and keep children within arm’s reach. The Yellowstone River adjacent to the monument is a cold, swift river; do not wade into the current above knee depth and wear a PFD if on the water. In summer, the butte face is exposed and hot (no shade) — carry water and a hat. The parking area is a gravel lot; watch for rattlesnakes in the grass adjacent to the parking area in summer. Respect the boardwalk safety, the river current and the summer heat.

BLM day-use entrance fee (America the Beautiful Pass accepted). No touching of Clark’s signature, any rock art or inscriptions, or any historical artifact. Stay on designated boardwalk trail only; no off-trail access to the butte face. Photography permitted (no flash on rock art). Pets on leash; pets not allowed on the boardwalk trail. No camping in the monument; the adjacent private campground provides camping. No collecting of rocks, fossils or archaeological materials. Check BLM for current hours, trail conditions and any seasonal closures before visiting.

Billings, Montana (28 miles west — the largest city in Montana, with Rimrock country, the Yellowstone Art Museum, MetraPark, and excellent dining and services), the Pictograph Cave State Park (just southwest of Billings — Montana’s most significant prehistoric rock-art site, with 4,000-year-old pictographs in three sandstone caves above the Yellowstone River), Makoshika State Park (60 miles east in Glendive — Montana’s finest badlands and dinosaur fossil landscape), Bighorn Canyon NRA (60 miles south via US-212 and MT-313 — the extraordinary canyon and Pryor Mountain mustang country), and the Little Bighorn Battlefield NM (55 miles south on I-90 — the most significant battlefield site of the Indian Wars era in Montana) define the region. Pompeys Pillar anchors the “Lewis and Clark trail east of Billings” experience and is an essential stop on any eastbound I-90 traverse of Montana.

Walk the boardwalk at your own pace and pause at Clark’s signature longer than you think you need to — the inscription (“Wm. Clark July 25 1806” carved directly into the Cretaceous sandstone, readable 220 years later in the original location) is one of the most moving historical artifacts in the American West, and the meaning accumulates the longer you stand there looking at it. Read Clark’s July 25, 1806 journal entry (available free online from the American Philosophical Society) before your visit — his description of climbing the rock, carving his name, and looking out over the Yellowstone valley transforms the experience from a historical curiosity to a personal and vivid moment in time. Combine the Pompeys Pillar visit with a stop at Pictograph Cave State Park just outside Billings (30 minutes from Pompeys Pillar) for the finest single day of historical and archaeological Montana experience east of the Rockies.