Lewis and Clark Expedition

From 1804 to 1806, a small United States Army party known as the Corps of Discovery, led by Captain Meriwether Lewis and William Clark, travelled from the Mississippi up the Missouri River, across the Rocky Mountains and down the Columbia River to the Pacific, then returned. Sent soon after the Louisiana Purchase, it mapped a vast region that was home to dozens of Indigenous nations, whose food, horses, guides and knowledge made the journey possible.

President Thomas Jefferson wanted a practical water route across the continent for commerce, and he wanted to assert American sovereignty over the peoples living along the Missouri before Britain or other powers could stake claims. Science was a secondary goal. Congress quietly provided $2,324. The party carried silver peace medals bearing Jefferson's portrait, flags and gifts, and was told to inform the nations it met that their lands now came under the authority of the United States.

The expedition left Camp Dubois, in Illinois, on 14 May 1804 and picked up Lewis at St. Charles. Accounts suggest up to 45 people took part, among them York, a Black man enslaved by Clark. Sergeant Charles Floyd died in August 1804, probably of appendicitis, the only member to die on the journey. On 25 September, near the mouth of the Bad River, the party met the Teton Lakota, who expected gifts in return for passage through their lands. A misjudged distribution of presents nearly led to violence until the chief Black Buffalo told his warriors to stand back, and the boats moved on to the Arikara villages.

The Corps spent the winter of 1804–1805 at Fort Mandan, near present-day Washburn, North Dakota, in Mandan territory, where Mandan chiefs met the captains in council and shared a ceremonial pipe. There they hired the French-Canadian trader Toussaint Charbonneau as an interpreter, together with his teenage wife Sacagawea. According to Charbonneau she was a Lemhi Shoshone who had been captured by Hidatsa raiders as a child around 1800, although Hidatsa oral tradition holds that she was Hidatsa. In February 1805 she gave birth to a son, Jean Baptiste, whom she carried for the rest of the journey.

The party headed west on 7 April 1805. Sacagawea rescued journals and records when a boat capsized in May. In August, while seeking horses from the Shoshone, the captains found that the leader, Cameahwait, was her brother, and the Shoshone agreed to trade horses and supply guides. Historians stress that she was not the expedition's guide, but her presence and her skill as an interpreter helped reassure the peoples they met. The Corps crossed the Continental Divide at Lemhi Pass, struggled over the Bitterroot Mountains and continued by canoe down the Clearwater, Snake and Columbia rivers.

The explorers first sighted the Pacific on 7 November 1805. On 24 November they voted on where to winter, with both Sacagawea and York taking part, and they built Fort Clatsop near present-day Astoria, Oregon, close to the Clatsop and Chinook peoples, from whom they sought food and news of trading ships. The homeward journey began on 23 March 1806. In July the captains divided their forces. Lewis's small group clashed with men of the Blackfeet nation, two of whom were killed, while Clark passed through Crow territory. The parties reunited on 11 August and reached St. Louis on 23 September 1806.

The expedition found no continuous waterway to the Pacific, but it produced about 140 maps, made contact with more than 70 tribes and described over 200 plant and animal species new to science, though long known to Indigenous peoples. Its flags, medals and declarations were also steps in a legal claim to Indigenous land under the doctrine of discovery. The members received double pay and land, but Clark refused to free York, who remained enslaved for at least a decade afterwards.

Our 1800 map shows the western half of North America shortly before the Louisiana Purchase, and our 1815 map shows it after the expedition, including the territory of the United States.