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Expeditions

Jefferson anticipated further westward settlements due to the Louisiana Purchase and arranged for the exploration and mapping of the uncharted territory. He sought to establish a U.S. claim ahead of competing European interests and to find the rumored Northwest Passage. Jefferson and others were influenced by exploration accounts of Le Page du Pratz in Louisiana (1763) and James Cook in the Pacific (1784), and they persuaded Congress in 1804 to fund an expedition to explore and map the newly acquired territory to the Pacific Ocean.

Jefferson appointed secretary Meriwether Lewis and acquaintance William Clark to lead the Corps of Discovery (1803–1806). In the months leading up to the expedition, Jefferson tutored Lewis in the sciences of mapping, botany, natural history, mineralogy, and astronomy and navigation, giving him unlimited access to his library at Monticello, which included the largest collection of books in the world on the subject of the geography and natural history of the North American continent, along with an impressive collection of maps.

The expedition lasted from May 1804 to September 1806 and obtained a wealth of scientific and geographic knowledge, including knowledge of many Indian tribes.

Jefferson organized three other western expeditions: the William Dunbar and George Hunter Expedition on the Ouachita River (1804–1805), the Thomas Freeman and Peter Custis Expedition (1806) on the Red River, and the Zebulon Pike Expedition (1806–1807) into the Rocky Mountains and the Southwest. All three produced valuable information about the American frontier.