Lewis & Clark National Historic TrailPage 223 of 235
Pompey's Pillar: What William Clark Saw in 1806, and What Climate Change Threatens
On July 25, 1806, returning east down the Yellowstone River with a small part of the expedition, Captain William Clark stopped at a large sandstone outcrop rising from the plains. He measured it, climbed to the top, and carved his name and the date among the petroglyphs left by Indigenous peoples, for whom Pompey's Pillar had long been a landmark and signpost. In his journal he praised the beautiful countryside and its abundant game.
Pompey's Pillar, rising from the plains along the Yellowstone River. Credit: National Park Service.
What has changed since
The view from the top has changed with the climate:
| What Clark saw | The threat now |
|---|---|
| Sagebrush steppe | More drought, higher temperatures and more frequent wildfires have shrunk it, threatening the greater sage-grouse that depend on it |
| The Yellowstone River | Warming water is making it less livable for native trout and helping smallmouth bass move in |
| The petroglyphs — and Clark's signature | Weathering from wind, moisture and temperature swings, likely worsening as the climate changes |
Sources
Based on "Pompey's Pillar," Lewis and Clark National Historic Trail, National Park Service; a work of the United States government in the public domain. It cites the Park Service's 2022 report Pittsburgh to the Pacific: High Potential Historic Sites of the Lewis and Clark National Historic Trail, William Clark's journal entry of July 25, 1806 (Gary E. Moulton, ed., Journals of the Lewis and Clark Expedition), and reporting on the site and the river.