No one was exactly sure how big the Louisiana Territory actually was. Some claimed it extended all the way to the Pacific Ocean, but Thomas Jefferson was content to accept the more moderate contention that the western border was the Rocky Mountains, leaving all land westward to the Spanish. However, no one knew exactly where the Rockies were, few Americans having ever seen them.
Even before the Louisiana Purchase Jefferson had been fascinated by the undiscovered frontier. Shortly following his inauguration, Jefferson had discussed the possibilities of exploration with his neighbor and personal secretary, Lieutenant Meriwether Lewis. Eventually, he chose Lewis to lead an expedition up the Missouri River and across the Rocky Mountains to chart the territory and observe and collect the species of the area for scientific purposes. In January 1803 Jefferson asked Congress to appropriate funds for this mission. Once the Louisiana Purchase was negotiated that April, the expedition was given the go-ahead. Meriwether Lewis was promoted to captain in the army, and Lieutenant William Clark was made second in command. Lewis and Clark gathered an expeditionary team of mostly military personnel, and spent the winter of 1803-1804 in St. Louis, preparing to venture into the wilderness.
In May 1804, the expedition set off from St. Louis with 45 soldiers. During the first year of the expedition, they took their boats north up the Missouri River, feeding on buffalo and deer, and warding off the sometimes-hostile natives. They made it to the Dakotas, where they wintered at the village of the Mandan Indians. It was there that Lewis and Clark hired the interpreting services of a French fur-trader, Toussaint Charbonneau, and his Indian wife Sacajawea. Though Charbonneau proved to be only of limited help, Sacajawea was indispensable as a guide, especially during the crossing of the Bitteroot Mountains in what is now southern Idaho. She showed the party how to forage for food, and was instrumental in maintaining good relations with the Indian tribes of what is now the northwest US. Once the expedition had crossed the mountains in Idaho, the party began the perilous trip down the Snake and Columbia Rivers. The group reached the mouth of the Columbia River, at the Pacific Ocean, on November 7, 1805. There they spent their second winter before beginning the journey home.
Lewis and Clark began the trip back to St. Louis in the spring of 1806, dividing their group into two to cover more territory at first. Lewis led the part of the group that took the northern track, and Clark led the remainder along a more southern trail. They met up again at the Mandan village where they had spent the first winter, and traveled quickly back to St. Louis on the Missouri River. The Lewis and Clark expedition landed at St. Louis in September 1806, having traveled nearly 3000 miles in two and a half years.
In Jefferson's proposal asking Congress to appropriate the funds necessary for the Lewis and Clark expedition, he highlighted the commercial possibilities it presented, to open up waterways and to divert southward the Indians' trade in pelts with Canada. He stressed the desire to find "the most practicable water communication across this continent, for the purpose of commerce." However, it is more likely that Jefferson's primary goal for the expedition was the collection of scientific data. He explicitly instructed Meriwether Lewis to learn as much as possible about the Native Americans, geological features, and plant and animal species of the Louisiana Territory. When Lewis and Clark returned, the specimens they had collected were sent to Philadelphia under top priority for scientific study. Jefferson himself experimented with growing the Indian corn that the expedition brought back.
Lewis and Clark have been canonized as American heroes for their amazing feat of exploration. Traveling 3000 miles in two and a half years was an unparalleled expeditionary accomplishment. The exploration of the Louisiana Territory demonstrated the truly vast area of the western lands purchased by the United States, and opened the nation's eyes to the resources and opportunities these lands held. Lewis and Clark's success paved the way for further exploration and settlement of the American West, which commenced soon after the US took possession of the territory in December 1803. Soon after they returned, America was abuzz with stories of the riches and wonders of the new territory. Legends circulated widely about gigantic Indians, soil too rich to grow trees, and a mountain composed entirely of salt. Jefferson believed many of the less far-fetched tall tales, and so did many of his countrymen. Despite the ridicule of certain political opponents, the Lewis and Clark expedition greatly stimulated interest in the West.