 Meriwether Lewis and William Clark began their famed expedition in 1804 with a party of thirty @-@ three people in three boats . Although they became the first Europeans to travel the entire length of the Missouri and reach the Pacific Ocean via the Columbia , they found no trace of the Northwest Passage . The maps made by Lewis and Clark , especially those of the Pacific Northwest region , provided a foundation for future explorers and emigrants . They also negotiated relations with multiple Native American tribes and wrote extensive reports on the climate , ecology and geology of the region . Many present @-@ day names of geographic features in the upper Missouri basin originated from their expedition . 
