The Lewis and Clark Expedition

Portrait of Thomas Jefferson
Portrait of Thomas Jefferson by James L. Dick

Thomas Jefferson was elected to the presidency in 1800. Two years later, he decided to organize an official, government-sponsored expedition to explore the upper reaches of the Missouri River and by so doing to find the elusive Northwest Passage to the Pacific Ocean. He chose Meriwether Lewis, his personal secretary, to lead the expedition. In January 1803, Lewis traveled to Philadelphia for intensive training with the leading American scientists, learning the use of scientific instruments, the rudiments of surveying, medicine, natural history and ethnology. In June 1803, Lewis asked William Clark, a friend from his former army service, to serve as co-leader of the expedition. Clark gladly agreed.

Jefferson’s final instructions to Lewis reflect the broad range of the president’s interests. The expedition was meant to prepare the way for the extension of the American fur trade and to advance geographical knowledge. Jefferson provided the best supplies, clothing, firearms, equipment, and rations then available. Lewis and Clark were instructed to observe and record the entire range of natural history and ethnology of the areas they explored, and note possible resources which would support future settlement. The Louisiana Purchase of 1803 had doubled the size of the nation, and a good share of the territory the expedition would explore was now officially part of the United States. Jefferson envisioned the nation’s eventual expansion to the Pacific, and wanted to strengthen the American claim to the northwest Columbia Basin.

Portrait of William Clark
Portrait of William Clark by Charles Wilson Peale

The Expedition Begins

In December 1803, William Clark established “Camp Wood” at the confluence of the Mississippi and Missouri rivers, north of St. Louis. While there he recruited and trained men, while Lewis spent time in St. Louis, conferring with traders about the Upper Missouri regions and obtaining maps made by earlier explorers. On May 14, 1804, the Corps of Discovery left Camp Wood. The party numbered 45, and included 27 young, unmarried soldiers, a French-Indian interpreter, Clark’s slave, York, and Lewis’s Newfoundland dog, Seaman. An additional group of men would travel only to the Mandan country for the first winter, and these included six soldiers and several French boatmen.

Travel up the Missouri River was difficult and exhausting due to heat, injuries, insects, and the troublesome river itself, with its strong current and many snags. The expedition used a keelboat and two small boats called pirogues to carry their supplies and equipment, averaging 15 miles per day. During this phase of the journey the group suffered the only casualty of the expedition. Sergeant Charles Floyd, who was buried near modern-day Sioux City, Iowa, died on August 20 from what is believed to be a ruptured appendix and consequent peritonitis. Relations with the tribes were generally good, and councils were held with the Otos, Missourias, and Yankton Sioux. However, a September 1804, council with the Teton Sioux near modern-day Pierre, South Dakota, almost resulted in disaster for the expedition. By October the Corps of Discovery reached the Mandan villages, near today’s Washburn, North Dakota. They built their second winter quarters (Fort Mandan) a few miles below the mouth of the Knife River, on the east bank of the Missouri River. During that cold winter of 1804-05, Lewis and Clark made copious notes in their journals, drew maps, and learned of the geography which lay ahead from American Indians in the area of their camp. They recruited an interpreter named Toussaint Charbonneau, who brought along his Shoshone wife, Sacagawea, and her newborn baby boy, Jean Baptiste.

Portrait of Meriwether Lewis
Portrait of Meriwether Lewis by Charles Wilson Peale

Westward to the Pacific

On April 7, 1805, Lewis and Clark sent the keelboat back to St. Louis with an extensive collection of zoological, botanical, and ethnological specimens as well as letters, reports, dispatches, and maps, and resumed their westward journey in two pirogues and six dugout canoes. The “corps of volunteers for the North Western Discovery,” now numbering 33, traveled into regions which had been explored and seen only by American Indians. By August 17 they reached the navigable limits of the Missouri River in the Rocky Mountains, and turned north up the Jefferson River. The expedition crossed the Continental Divide through Lemhi Pass, and purchased horses from the Shoshones, Sacagawea’s people. They traveled north to Lolo Pass where they crossed the Bitteroot Range on the Lolo Trail; this was the most difficult part of the journey. Lewis and Clark reached the country of the Nez Perce on the Clearwater River in Idaho, and left their horses for dugout canoes. From there they made their way down the Clearwater, Snake, and Columbia rivers, reaching the Pacific Ocean by November 1805.

In December the expedition members built Fort Clatsop on the south side of the Columbia River (near present-day Astoria, Oregon), and settled in for the winter. Lewis and Clark accomplished considerable scientific work, gathering and recording information regarding the country and its inhabitants, despite near-constant rain and plaguing insects. In addition to establishing a salt camp, the men hunted (131 elk and 20 deer) and made 358 pairs of moccasins.


The Return Journey

The return trip began on March 23, 1806. After a tough journey up the Columbia River against strong currents, the party retrieved their horses from the Nez Perce, and waited for the deep mountain snows to melt. After crossing the Bitteroots the party split at the Lolo Pass to add to the geographical knowledge they could gather. Confident of their survival, Lewis went north while Clark went south to the Yellowstone River. While on the Marias River, Lewis’s small party had a fight with a party of Piegan Blackfeet in which two Blackfeet were killed. This was the only violent incident of the entire journey. The Corps of Discovery was reunited in North Dakota, at the mouth of the Yellowstone River. They left Charbonneau and Sacagawea at the Mandan villages, continued down the Missouri River, and returned to St. Louis on September 23, 1806.

The Importance of the Journey

The results and accomplishments of the Lewis and Clark Expedition were extensive. It altered the imperial struggle for control of North America, particularly in the Pacific Northwest, by strengthening the U.S. claim to the areas now including the states of Oregon and Washington. Lewis and Clark achieved an impressive record of peaceful cooperation with the different tribes and generated American interest in the fur trade. This had a far-reaching effect, since it led to further exploration and commercial exploitation of the West. Lewis and Clark added to geographic knowledge by determining the true course of the Upper Missouri and its major tributaries, and producing important maps of these areas. They forever destroyed the dream of a Northwest Passage, but proved the success of overland travel to the Pacific. The expedition compiled the first general survey of life and material culture of the tribes they encountered.

Lewis and Clark made significant additions to the zoological and botanical knowledge of the continent, providing the first scientific descriptions of many new species of animals, including the grizzly bear, prairie dog, pronghorn (antelope), and mountain goat. They made the first attempt at a systematic record of the meteorology of the West, and less successfully attempted to determine the latitude and longitude of significant geographical points.

The members of the Lewis and Clark Expedition traveled over 8,000 miles in less than 2 ½ years, losing only one member of their party, at a cost to the taxpayer of $40,000. By any measure of scientific exploration, the Lewis and Clark Expedition—the nation’s first “road trip”—was phenomenally successful in terms of accomplishing its stated goals, expanding human knowledge, and spurring further curiosity and wonder about the American West.

Last updated: September 16, 2020

Park footer

Contact Info

Mailing Address:

508 East 2nd Street
Yankton, SD 57078


605-665-0209 x21

Contact Us