Lewis and Clark Expedition: Scouting ahead of the expedition, Meriwether Lewis and four companions sight the Great Falls of the Missouri River.

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.

Meriwether Lewis was an American explorer, soldier, politician, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition, also known as the Corps of Discovery, with William Clark. Their mission was to explore the territory of the Louisiana Purchase, establish trade with, and sovereignty over the natives near the Missouri River, and claim the Pacific Northwest and Oregon Country for the United States before European nations. They also collected scientific data and information on indigenous nations. President Thomas Jefferson appointed him Governor of Upper Louisiana in 1806. He died in 1809 of gunshot wounds, in what was either a murder or suicide.

The Great Falls of the Missouri River are a series of waterfalls on the upper Missouri River in north-central Montana in the United States. From upstream to downstream, the five falls along a 10-mile (16 km) segment of the river are:

• Black Eagle Falls
• Colter Falls
• Rainbow Falls
• Crooked Falls, also known as Horseshoe Falls
• Big Falls, also known as the Great Falls,