In 1803, President Thomas Jefferson purchased the Louisiana Territory from France for $11.25 million. The territory was understood to be the land west of the Mississippi to its Missouri headwaters, and north of the Arkansas River to the 49th parallel. Jefferson engaged his personal secretary, Meriwether Lewis, to head an expedition to explore this new American territory and to search for a passage from the Missouri River to the headwaters of the Columbia River. Lewis in turn chose William Clark to be the cocommander of what Jefferson called the Corps of Discovery.
The two captains, three sergeants, 23 enlisted men, and Clark’s black slave, York, left St. Louis in May 1804. In North Dakota they were joined by French trader Toussaint Charbonneau, who had traveled widely on the upper Missouri and spoke several Indian languages. One of Charbonneau’s wives, a 15-year-old Shoshone girl named Sacagawea, gave birth during the spring. Lewis and Clark hired Charbonneau as interpreter and allowed the young mother and baby to accompany the Corps, as they later expected to travel through Shoshone territory.
The Corps entered Montana on April 26, 1805, passing the confluence of the Missouri and the Yellowstone Rivers. They wound their way up the Missouri, traveling in pirogues, huge French-Canadian dugout canoes. By July 25 they were at the Three Forks of the Missouri and were heartened by Sacagawea’s claim that they were near her homeland. Nineteen days later, near Lemhi Pass, Lewis encountered the expedition’s first Montana Indian (a Shoshone, who led them to Sacagawea’s brother). They beached their pirogues, traded for horses, and proceeded down the Bitterroot Valley . On September 13 they crossed Lolo Pass out of Montana toward the Pacific Coast.
After a hungry and flea-ridden winter on the Oregon coast, the Corps started back up the Columbia. They backtracked to Lolo Pass and crossed into Montana on June 27, 1806. On July 1, at the point where Lolo Creek meets the Bitterroot River, the expedition divided. Clark took part of the Corps and retraced the previous journey to the Missouri headwaters, but this time followed the Gallatin River over the Bozeman Pass in order to explore the Yellowstone River Valley. Lewis took the rest of the men and followed old Indian trails up the Blackfoot River and then over the Rockies to the Great Falls in order to scout a more direct passage over the Continental Divide. While Clark had an uneventful journey down the Yellowstone, Lewis had a confrontation with a group of Blackfeet that left two Indian warriors dead.
The two parties met at the confluence of the Yellowstone and the Missouri on August 12. By September 23, 1806, they were in St. Louis. This amazing journey had an almost immediate impact on the history of Montana. Members of the Corps retold stories of vast amounts of wildlife, especially fur-bearing mammals. Within a year, the first fur trading fort was built in Montana.