Celilo Falls was a tribal fishing area on the Columbia River, just east of the Cascade Mountains, on what is today the border between the U.S. states of Oregon and Washington. The name refers to a series of cascades and waterfalls on the river, as well as to the native settlements and trading villages that existed there in various configurations for 15,000 years. Celilo was the oldest continuously inhabited community on the North American continent until 1957, when the falls and nearby settlements were submerged by the construction of The Dalles Dam. In 2019, there were calls by tribal leaders to restore the falls.

The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the United States expedition to cross the newly acquired western portion of the country after the Louisiana Purchase. The Corps of Discovery was a select group of U.S. Army and civilian volunteers under the command of Captain Meriwether Lewis and his close friend Second Lieutenant William Clark. Clark, along with 30 others, set out from Camp Dubois, Illinois, on May 14, 1804, met Lewis and ten other members of the group in St. Charles, Missouri, then went up the Missouri River. The expedition crossed the Continental Divide of the Americas near the Lemhi Pass, eventually coming to the Columbia River, and the Pacific Ocean in 1805. The return voyage began on March 23, 1806, at Fort Clatsop, Oregon, ending six months later on September 23 of that year.