The Lewis and Clark Expedition

Even before the Louisiana Purchase, Jefferson believed the United States should stretch across the continent. In a secret message of January 18, 1803 — when the territory still belonged to France — he asked Congress for $2,500 to explore the West to the Pacific, explaining the request mainly in terms of promoting commerce.

Jefferson instructed Lewis, his former private secretary, to seek a practical water route across the continent, to establish relations and trade with western Native nations, and to report on the geography, geology, astronomy, plants, animals, and climate of the West. Lewis chose William Clark as co-commander. Jefferson helped plan supplies: arms, food, medicine, scientific instruments, and gifts for Native leaders.

The Corps left the St. Louis area in May 1804 and worked up the Missouri. After five months they built Fort Mandan near the Mandan villages in present-day North Dakota, 1,600 miles upriver, and wintered there. They hired the French-Canadian trader Toussaint Charbonneau and his young wife, Sacagawea, a Lemhi Shoshone who had been captured by the Hidatsa as a girl. With their two-month-old son, Jean Baptiste, she set out with the Corps in April 1805. Along the Lemhi River in present-day Idaho, her people provided horses and a guide for the crossing of the Continental Divide. York, enslaved by Clark, hunted and labored alongside the others; the National Park Service credits him as the first African American known to have crossed North America.

The Corps crossed the mountains and descended the Columbia River, reaching its estuary in November 1805 — Clark wrote of the “joy” of seeing the ocean on November 7 — and wintered on the Pacific coast. On the way home in July 1806 the expedition split into groups to explore more of the Missouri and Yellowstone drainages; Sacagawea guided Clark’s party over Bozeman Pass into the Yellowstone Valley. The Corps reached St. Louis on September 23, 1806.

The expedition did not find an all-water route to the Pacific, because none existed. But it brought back maps, journals, and specimens that gave the U.S. government its first detailed view of the lands west of the Mississippi, and it strengthened American claims to the Oregon Country.

Lewis and Clark became national heroes, and their journey a symbol of American exploration. The route crossed the territories of more than sixty Native nations, for whom the expedition was a harbinger of traders, settlers, soldiers, and treaties that would take most of their lands. After the expedition returned, York was denied his payment and his freedom. Sacagawea returned to the Mandan and Hidatsa villages in 1806; her role, little recognized at the time, was celebrated only much later.