way out from St. Louis starting in 1804

return in 1806

Lewis and Clark Expedition, first United States overland exploration of the American West and Pacific Northwest, beginning in May 1804 and ending in September 1806. The expedition was commissioned by President Thomas Jefferson and led by army officers Meriwether Lewis and William Clark. The exploration covered a total of about 13,000 km (about 8000 mi), from a camp outside St. Louis to the Pacific Ocean and back. Like other scholars in his time, Jefferson believed in the existence of a Northwest Passage, or some kind of water connection between the Atlantic and Pacific Oceans. The principal goal of the expedition was to locate such a route and survey its potential as a waterway for American westward expansion. Although Lewis and Clark did not find this route, the expedition succeeded in making peaceful contact with Native Americans and uncovering a wealth of knowledge about the peoples, geography, plants, and animals of the western United States.

Thomas Jefferson had repeatedly insisted that the Corps of Discovery had one central mission—to find what he called “the most direct and practicable water communication across this continent for the purposes of commerce.” However, Lewis and Clark did not find a Northwest Passage, nor did they pioneer the route that became the Oregon Trail. Although Lewis and Clark strengthened U.S. claims in the West, American claims in subsequent diplomatic disputes with Britain were based not so much on Lewis and Clark as on the Columbia River explorations of American explorer Captain Robert Gray in 1792 and the building of Fort Astoria in 1811. But Jefferson was by no means disappointed with his Corps of Discovery. The journals, maps, plant and animal specimens, and notes on Native American societies amounted to a western encyclopedia. The expedition also established peaceful contact with many Native American peoples. Finally, the expedition set a pattern for government-sponsored scientific exploration in the United States