Jefferson quickly launched four government-financed expeditions up the river valleys of the new territory to establish relationships with Indian tribes and to determine Spanish influence and presence. The first set out in 1804 to explore the upper reaches of the Missouri River. Jefferson appointed twenty-eight-year-old Meriwether Lewis, his secretary, to head the expedition and instructed him to investigate Indian cultures, to collect plant and animal specimens, and to chart the geography of the West. (See “Visualizing History.”) Congress wanted the expedition to scout locations for military posts, negotiate fur trade agreements, and identify river routes to the West (see Map 10.2).

For his co-leader, Lewis chose Kentuckian William Clark, a veteran of the 1790s Indian wars. With a crew of forty-five, including expert rivermen, gunsmiths, hunters, interpreters, a cook, and Clark’s slave named York, the explorers left St. Louis in the spring of 1804, working their way northwest up the Missouri River. They camped for the winter at a Mandan village in what is now central North Dakota. The Mandan Indians were familiar with British and French traders from Canada, but the black man York created a sensation. Reportedly, the Indians rubbed moistened fingers over the man’s skin to see whether the color was painted on.

The following spring, the explorers headed west, accompanied by a sixteen-year-old Shoshoni woman named Sacajawea. Kidnapped by Mandans at about age ten, she had been sold to a French trapper as a slave/wife. Hers was not a unique story among Indian women; such women knew several languages, making them valuable translators and mediators. Further, Sacajawea and her new baby allowed the American expedition to appear peaceful to suspicious tribes. As Lewis wrote in his journal, “No woman ever accompanies a war party of Indians in this quarter.”

The Lewis and Clark expedition reached the Pacific Ocean at the mouth of the Columbia River in November 1805. When the two leaders returned home the following year, they were greeted as national heroes. They had established favorable relations with dozens of Indian tribes; they had collected invaluable information on the peoples, soils, plants, animals, and geography of the West; and they had inspired a nation of restless explorers and solitary imitators.