The Lewis and Clark Expedition

Shortly after completing the Louisiana Purchase, in keeping with his wide interest in science, President Jefferson planned a mission to investigate the new territory. On June 20, 1803, he sent a letter to Captain Meriwether Lewis of the 1st US Infantry. He wrote: "The Object of your mission is to explore the Missouri river & such principal streams of it as by its course and communication with the waters of the Pacific ocean, whether the Columbia, Oregon, Colorado or any other river, may offer the most direct & practicable water communication across this continent for the purpose of commerce."

Captain Lewis and Lieutenant William Clark set out within weeks. Lewis and Clark led their party of about 40 soldiers across the continent in a two-year journey. They were guided by French-Canadian fur trapper named Toussaint Charbonneau and his Shoshone wife, Saca-jawea, who also acted as translator in the party's dealing with Indian tribes. They built Ft. Mandan in the Dakota Territory, where they spent the first winter, and eventually reached the Oregon coast. In the spring of 1805 they sent samples of wildlife back to Jefferson, including a live prairie dog. In addition to providing detailed information about the newly acquired western regions, their travels also gave America claim to the Oregon Territory; it would be decades before those rights were assured. Jefferson also sent Zebulon Pike on a similar mission. Pike helped establish the notion of the Great Plains as the "Great American Desert." He also explored the Colorado Rockies and discovered the peak named for him.