The Lewis and Clark expedition, which began in 1804 and took more than two years to complete, had three purposes: to map a route that would be part of a passage between the Atlantic and Pacific Oceans; to trace the boundaries of the Louisiana Purchase; and to claim the Oregon territory for the United States. President Thomas Jefferson (1743–1826) commissioned the expedition, which was officially called the Corps of Discovery and was headed by army officers Meriwether Lewis (1774–1809) and William Clark (1770–1838).
Jefferson believed that the nation that controlled a waterway between the Atlantic and Pacific Oceans would dominate North America. He also predicted that the West would prove to be fertile land for American farmers and wanted to open up routes for settlement. In 1803 the United States bought a vast area (800,000 square miles) west of the Mississippi River from France in what was known as the Louisiana Purchase. Jefferson directed Lewis and Clark to map this area and to announce to its residents that the territory was under U.S. control.
The Corps of Discovery made preparations at its base camp in St. Louis, Missouri. Lewis would serve as the naturalist (a person who studies plants and animals in their natural environment), and Clark would be the mapmaker and negotiator. Approximately forty-eight men (including soldiers, civilian hunters, and French boatmen) formed part of the corps when it began the trek up the Missouri River on May 21, 1804. The men wintered at Mandan (in present-day North Dakota), where they built a fort. During the second travel season the corps, which now consisted of thirty-three members, included the Shoshone woman Sacagawea (1786?–1812) and her French Canadian interpreter husband Toussaint Charbonneau. The party portaged (carried boats from one body of water to another) around the Great Falls of Missouri, searching for a passage over the Continental Divide, the ridge of the Rocky Mountains that forms a watershed separating rivers that flow east from rivers that flow west. They labored through the deep snow of the Lolo Trail (present-day Idaho and Montana). Then the corps boated on the Snake River into present-day Washington State, before finally reaching the Columbia River. With the translating assistance of Sacagawea, Lewis and Clark enjoyed friendly relations with the Native Americans in the region. In November 1805 the party arrived at the Pacific Ocean, where they built Fort Clatsop. On the return trip the following spring, Clark led a group up the Yellowstone River, while Lewis explored north-central Montana. After reuniting on the Missouri River, the explorers continued to St. Louis, as planned.
Although Lewis and Clark did not find the water route through the American West, they peacefully contacted the Native Americans in the region and gained extensive knowledge about the geography, people, plants, and animals of what would later become the western United States.
Further Information: Blumberg, Rhoda R. The Incredible Journey of Lewis and Clark. New York: Morrow, 1995; Bowen, Andy R. The Back of the Beyond: A Story about Lewis and Clark. Minneapolis, Minn.: Lerner, 1996; Duncan, Dayton. "If Lewis and Clark Came Back Today." American Heritage. November, 1997, pp. 70–75; Hall, Eleanor J. The Lewis and Clark Expedition. San Diego: Lucent, 1996; PBS. The West. [Online] Available http://www.pbs.org/weta/thewest/, October 22, 2000; St. George, Judith. Sacagawea. New York: Putnam, 1997. White, Alana J. Sacagawea: Westward with Lewis and Clark. Springfield, N.J.: Enslow, 1997.