Corps of Discovery

Jefferson's Instructions

Before Meriwether Lewis and William Clark set out on their historic expedition into the newly acquired Louisiana Territory, they received detailed instructions from President Thomas Jefferson. These directives reflected Jefferson’s wide-ranging interests in science, commerce, and geography. He envisioned the journey as a means to expand the American fur trade, enhance geographic knowledge, and assert U.S. claims to the Pacific Northwest.

You can read the full primary source text of Thomas Jefferson’s instructions to Meriwether Lewis, dated June 20, 1803, at the Library of Congress via this link: Jefferson’s Instructions to Meriwether Lewis (Full Transcript)

It outlines Jefferson’s detailed expectations for the expedition, including:

• Mapping the Missouri River and identifying a water route to the Pacific.

• Observing and recording geographic, botanical, zoological, and meteorological data.

• Establishing peaceful relations and trade with Native American tribes.

• Gathering ethnographic information about Indigenous cultures.

• Exploring the potential for future commerce and settlement.

Jefferson ensured the explorers were well-equipped with the best supplies, firearms, clothing, and provisions available. Although the expedition did not find a direct water route across the continent, its scientific and diplomatic achievements made it one of the most successful explorations in history.

The Expedition Begins

In December 1803 William Clark established "Camp River Dubois" at the confluence of the Mississippi and Missouri Rivers, just north of St. Louis. Lewis and Clark State Historic Site operates a museum there today. While there Clark recruited and trained men for the Corps of Discovery, 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 William Clark and the Corps of Discovery left Camp River Dubois, and were joined by Meriwether Lewis in St. Charles, Missouri. The expedition included over 45 members: 27 young, unmarried soldiers, a French-Canadian interpreter, York, who had been enslaved by William Clark since his childhood, and Seaman, a Newfoundland dog belonging to Lewis. Additional men, including six soldiers and several French boatmen (engagés), accompanied the group only as far as the Mandan villages.

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 specially built keelboat and two smaller 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, Sgt. Charles Floyd. Most historians now believe that Floyd died of a burst appendix. He is buried near modern-day Sioux City, Iowa. Relations with Native Americans were generally peaceful. The Corps held councils with the Oto and Missouri tribes, presenting peace medals to key leaders. By October, they reached the the Mandan and Hidatsa villages, where they built "Fort Mandan" (near present-day Washburn, North Dakota), and spent the winter of 1804-1805.

During that winter, Lewis and Clark recorded extensive notes in their journals, drew maps, and gathered intelligence from folks in the Mandan and Hidatsa villages. They recruited an interpreter named Toussaint Charbonneau, who brought along his Shoshone wife, Sacagawea, and her newborn baby boy, Jean Baptiste.

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 Discovery, now numbering 33, traveled into regions previously known only to Native peoples.

After crossing most of modern-day Montana, the explorers were held up for over a month by the extensive waterfalls at Great Falls. Lewis tried to use a special collapsible boat he had manufactured at Harpers Ferry, but the animal skins could not be sealed over the boat's iron frame and it had to be abandoned.

By August 17, they reached the navigable limits of the Missouri River near the Rocky Mountains, and turned south up the Jefferson River. After crossing the Continental Divide at Lemhi Pass, they obtained horses from the Shoshone, 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. Nearly starved, Lewis and Clark reached the country of the Nez Perce on the Clearwater River in Idaho. They left their horses in the care of the Nez Perce and continued their travels in dugout canoes they made. From there they floated down the Clearwater, Snake, and Columbia rivers, reaching the Pacific Ocean by November of 1805.

In December the explorers 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 while on the Pacific coast, gathering and recording information regarding the country and its inhabitants, despite constant rain and plaguing insects. A detail of men was assigned to make salt by boiling sea water.

The Return Journey

On March 23, 1806 the return trip began. After a tough journey up the Columbia against strong currents, the party retrieved their horses from the Nez Perce and waited for the deep mountain snow to melt before crossing the Bitterroots again.

At the Lolo Pass, the group split to explore more territory and add to the geographical knowledge they would gather. Lewis went north while Clark went south. While on the Marias River Lewis' party had a fight with a hostile group of Blackfeet, resulting in the only violent conflict of the expedition in which two Blackfeet were killed.

The Corps reunited in North Dakota at the mouth of the Yellowstone River. They left Charbonneau, Sacagawea, and the baby at the Mandan villages, continued down the Missouri River, and arrived triumphantly in St. Louis on September 23, 1806.

The Importance Of The Expedition

The Lewis and Clark Expedition had far-reaching consequences. It strengthened the U.S. claim to the Pacific Northwest, particularly in what are now Oregon and Washington. Overwhelmingly peaceful interactions with many Native tribes set a precedent for diplomacy, though it also paved the way for future expansion and displacement. The journey also generated American interest in the fur trade, which 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 Native cultures they encountered.

Lewis and Clark documented over 200 plant species and 120 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.

Lewis and Clark traveled over 8,000 miles in less than 2 1/2 years, losing only one member of their party, at a total cost to the taxpayer of $40,000. By any measure of scientific exploration, the Lewis and Clark expedition was phenomenally successful in terms of accomplishing its stated goals, expanding human knowledge, and spurring further curiosity and wonder about the vast American West.