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Primary sourceArtifactcarved 25 July 1806; designated monument 2001

Pompeys Pillar National Monument

William Clark · carved 25 July 1806; designated monument 2001

A sandstone rock formation in Montana that William Clark named after Sacagawea's son and carved his signature upon in 1806.

Clark named this landmark after Sacagawea's son and his carved signature is the expedition's only surviving physical trace.

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A tall, flat-topped sandstone rock formation rises above a green and golden grassy field under a clear blue sky. Dark trees stand at the left and right edges, and a small white tent-like structure sits at the base.
Pompeys Pillar National Monument, Montana. Designated 2001.

About this source

What it is

Pompeys Pillar is a sandstone rock formation in south-central Montana. It was designated a U.S. National Monument in 2001 and is managed by the Bureau of Land Management. The pillar bears Native American petroglyphs as well as William Clark's carved signature and the date July 25, 1806.

Why it matters

Clark named the rock after Jean-Baptiste Charbonneau, Sacagawea's infant son, whom he nicknamed 'Pompey.' His carved signature is the only physical evidence still surviving along the expedition's route, directly connecting the landscape to Sacagawea's family and the journey she undertook.

Look closer

  • Why might Clark have chosen to name this landmark after Sacagawea's son rather than after her?
  • What does the survival of Clark's signature, but not other traces of the expedition, tell us about how history gets remembered?
  • What do the other petroglyphs and carvings on the rock add to the story that Clark's signature alone does not?

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Diary entry

Primary source

Journals of the Lewis and Clark Expedition

Meriwether Lewis and William Clark · 1804–1806

Handwritten manuscript page in brown ink on aged paper, numbered 7 in the top right corner, with many words struck through and revised. The text describes travel to the forks of Jefferson's river, meeting Captain Lewis, and dealings with Shoshone natives and a mountain crossing.Letter

Primary source

William Clark's Letter to Toussaint Charbonneau

William Clark · 20 August 1806

Handwritten manuscript page headed 'Confidential' and 'Gentlemen of the Senate and of the House of Representatives', written in brown ink on aged paper, discussing trading houses with Indian tribes and federal policy.Document

Primary source

Jefferson's Secret Message to Congress Regarding the Lewis and Clark Expedition

Thomas Jefferson · 18 January 1803

Document

Primary source

Louisiana Purchase Treaty

30 April 1803

Book

Secondary source

The Conquest: The True Story of Lewis and Clark

Eva Emery Dye · 1902

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