Within a year of the purchase, Jefferson dispatched an expedition led by Meriwether Lewis and William Clark, two Virginia-born veterans of Indian wars in the Ohio Valley, to explore the new territory. Their objects were both scientific and commercial—to study the area’s plants, animal life, and geography, and to discover how the region could be exploited economically. Jefferson hoped the explorers would establish trading relations with western Indians and locate a water route to the Pacific Ocean—an updated version of the old dream of a Northwest Passage that could facilitate commerce with Asia.

A page from William Clark’s journal of the Lewis and Clark expedition, depicting a salmon. Among their tasks was to record information about the West’s plants, animal life, and geography.

In the spring of 1804, Lewis and Clark’s fifty-member “corps of discovery” set out from St. Louis on the most famous exploring party in American history. They spent the winter in the area of present-day North Dakota and then resumed their journey in April 1805. They were now accompanied by a fifteen-year-old Shoshone Indian woman, Sacajawea, the wife of a French fur trader, who served as their guide and interpreter. After crossing the Rocky Mountains, the expedition reached the Pacific Ocean in the area of present-day Oregon (which lay beyond the nation’s new boundaries) in November 1805. They returned in 1806, bringing with them an immense amount of information about the region as well as numerous plant and animal specimens. Reports about geography, plant and animal life, and Indian cultures filled their daily journals. Although Lewis and Clark failed to find a commercial route to Asia, they demonstrated the possibility of overland travel to the Pacific coast. They found Indians in the trans-Mississippi West accustomed to dealing with European traders and already connected to global markets. The success of their journey helped to strengthen the idea that American territory was destined to reach all the way to the Pacific.

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