Lewis and Clark Expedition (May 14, 1804-September 23, 1806), an expedition sent by President Thomas Jefferson to examine the resources of the far Northwest. The 8,000-mile (12,900-km) journey from the Mississippi River to the Pacific Coast and back again was led by Meriwether Lewis and William Clark.

The expedition provided valuable information about the climate, geography, natural products, and plant and animal life of the region, and about the customs, dress, and economy of the Indians. The exploration helped establish the legal claim the United States later made for the territory, and it opened a route that was soon traveled by settlers and traders. One aim was unfulfilled: Lewis and Clark failed to find a practical water route all the way from the Mississippi to the Pacific, for none exists.

Important dates in the Lewis and Clark expedition
1803
January 18President Thomas Jefferson asked Congress to finance an expedition to explore the western part of North America. Congress quickly approved the request.
May 2 U.S. representatives signed a treaty with France to purchase the Louisiana Territory.
June 19Captain Meriwether Lewis, Jefferson’s choice to lead the expedition, asked William Clark to serve as co-leader.
August 31Lewis launched the expedition’s boat down the Ohio River from Pittsburgh, Pennsylvania.
October 15Lewis and Clark met in Clarksville, Indiana, where Clark had recruited men for the expedition.
December 13The expedition established winter quarters at Camp Dubois, near St. Louis, Missouri.
1804
May 14The expedition set out from Camp Dubois and headed up the Missouri River.
August 20Sergeant Charles Floyd became the expedition’s only member to die on the journey.
October 24The group began to build Fort Mandan in present-day North Dakota for its winter camp.
November 4Lewis and Clark hired the French-Canadian fur trader Toussaint Charbonneau and his Shoshone Indian wife Sacagawea to interpret Indian languages.
1805
April 7The journey resumed up the Missouri River.
June 13The group reached the Great Falls of the Missouri River and soon began an 18-mile (29-kilometer) overland trip around the waterfalls.
September 11The expedition entered the Lolo Trail of the Bitterroot Range in the Rocky Mountains. The party spent 11 days crossing the mountains under severe conditions.
November 18Members of the expedition reached the Pacific coast.
December 7The expedition began to build Fort Clatsop in present-day Oregon for its winter quarters.
1806
March 23The homeward journey started.
July 3The expedition split into two groups to find a shortcut home and to explore more of the Louisiana Territory.
July 27Lewis’s group killed two Blackfeet Indians who tried to steal guns and horses in what was the only bloodshed on the entire trip.
August 12The two groups of explorers reunited on the Missouri River, near the mouth of the Yellowstone River.
September 23The expedition arrived back in St. Louis.