The Lewis and Clark Expedition lasted 862 days. The Corps of Discovery departed near St. Louis in May 1804 and returned in September 1806 after exploring the western lands acquired through the Louisiana Purchase.
President Thomas Jefferson commissioned the expedition after the 1803 purchase from France. Captain Meriwether Lewis and Second Lieutenant William Clark led the group, whose goals included mapping territory, studying plants and animals, identifying routes, and establishing relations with Indigenous nations.
The expedition crossed the Rocky Mountains and reached the Pacific Ocean in late 1805. Sacagawea traveled with the party and helped communicate with some Indigenous communities; her presence also signaled peaceful intentions. York, an enslaved man owned by Clark, was another notable member.
The journey was not a nonstop trek. The Corps wintered at Fort Clatsop near the Pacific coast before beginning its return. Sergeant Charles Floyd died during the expedition, the only member of the Corps known to have died during the journey.