In their cross-country trip to the Pacific Ocean, Captain Meriwether Lewis and Second Lieutenant William Clark went through Missouri, Kansas, Nebraska, Iowa, North and South Dakota, Montana, Idaho, Oregon, and Washington. The journey took more than two years, and the explorers maintained detailed journals of the geography, route, natives and natural history.
In May 1804, the 33-member Corps of Discovery left St. Louis. This small group of army volunteers was commissioned specifically by President Thomas Jefferson to explore the northern expanse of America's new Louisiana Purchase, and then to move beyond it in search of an all-water route to the Pacific Ocean.
The expedition followed the Missouri River to its headwaters in Western Montana, then found they had to leave the river and portage their canoes to cross the Continental Divide at Lemhi Pass. Here they found a well-traveled Native American path as they crossed into Idaho, the first white men to see this area. Not far past the pass, they entered the Clearwater River, then the Snake River and Columbia River. On Nov. 7, 1805, they reached the Pacific Ocean. Here they built Fort Clatsop on the Oregon side of the Columbia River, staying the winter so the men could rest and also establishing an American presence in this unclaimed land. While the expedition explored other river routes on the way back, they never discovered an all-water route to the Pacific.