The Lewis and Clark Expedition

May 14, 1804–September 23, 1806

The Lewis and Clark Expedition (1804–1806) was a military expedition that explored the upper regions of the Louisiana Purchase from St. Louis westward to present-day Astoria, Oregon. The expedition was the first overland expedition conducted by the United States government and was a major achievement that helped open the American West for the fulfillment of Manifest Destiny.

Sacagawea, Lewis and Clark Expedition

Sacagawea with Lewis and Clark. Image Source: Wikipedia.

Lewis and Clark Expedition Summary

The Lewis and Clark Expedition was a military expedition that took place from May 14, 1804, to September 23, 1806. The expedition was led by Meriwether Lewis and William Clark and the purpose was to explore the western frontier and find a water route from the Mississippi River to the Pacific Ocean. The territory included land the United States acquired from France in the Louisiana Purchase. As a result, Lewis and Clark were also instructed by President Thomas Jefferson to establish trade relationships with the Native American Indian tribes in the region. The expedition included a group of soldiers that are known as the “Corps of Discovery.” The expedition set out from St. Louis, Missouri, and traveled westward, crossing the Great Plains. Over the winter of 1804, a Canadian trader, Toussaint Charbonneau, and his wife, a young Shoshone woman named Sacajawea, joined the expedition. The journey resumed in the spring, crossing over the Continental Divide, the Rocky Mountains, and the Columbia River Plateau. The expedition reached the Pacific Ocean in November 1805, and it returned to St. Louis in September 1806. Along the way, they contacted various tribes, including the Shoshone, Nez Perce, and Blackfeet. They also carefully documented the plants and animals they found, and mapped the rivers and waterways. Overall, the Lewis and Clark Expedition was a major achievement that helped to open the American West to expansion. It inspired further exploration of the territory, settlement, and eventually the concept of “Manifest Destiny.”

Lewis and Clark Expedition Facts

  • Also Known As: The Lewis and Clark Expedition is also referred to as the “Corps of Discovery.”
  • Date Started: The expedition started on Monday, May 14, 1804.
  • Date Ended: It ended on Tuesday, September 23, 1806.
  • Miles Traveled: It is estimated the Lewis and Clark Expedition traveled more than 8,000 miles.
  • Fun Fact: Jean Baptiste Charbonneau was born on February 11, 1805, during the expedition. He was the son of Toussaint Charbonneau and Sacajawea. William Clark nicknamed him “Little Pomp.”
Lewis and Clark Expedition, Encounter Chinooks, Painting
This painting depicts the Corps of Discovery encountering meet Chinooks on the Lower Columbia. Image Source: Wikipedia.

History and Overview of the Lewis and Clark Expedition

The Lewis and Clark expedition — also known as the Corps of Discovery — was the first – and extremely ambitious — overland expedition to the Pacific coast and back that was undertaken by the United States. At the time of the expedition, the United States had just acquired the Louisiana Territory from France in the Louisiana Purchase and most Americans had no idea what lay west of the Mississippi River. President Thomas Jefferson, who commissioned the expedition, even believed it was possible that prehistoric creatures such as mastodons still existed in the territory.

Jefferson’s Secret Expedition to the West

Although many people believe Thomas Jefferson planned the expedition after the Louisiana Purchase was completed, it is not incorrect. Jefferson actually conceived the plan by the early part of 1803 — months before the purchase was completed — and asked Congress for $2,500 to send a military expedition into French territory. 

Meriwether Lewis

Jefferson provided detailed orders for the expedition, which were given to the man he chose to lead it — his private secretary, 28-year-old Captain Meriwether Lewis. Lewis was a frontier veteran and an experienced officer, having served under General Anthony Wayne during the Northwest Indian War.

Meriwether Lewis, Lewis and Clark Expedition
Meriwether Lewis. Image Source: Wikipedia.

Purpose of the Lewis and Clark Expedition

The purpose of the expedition was to find an all-water route — over rivers and lakes — from St. Louis to the Pacific Ocean. Jefferson also wanted Lewis and his men to take careful measurements of latitude and longitude, record their findings, and document the land, its inhabitants, and the natural resources. Jefferson also wanted Lewis to meet with the leaders of the Indian Tribes in the territory and set up trade relationships with them. Jefferson was intent on becoming involved in the fur trade in the territory by establishing an American presence. To that end, Jefferson gave Lewis silver medallions to give to the chiefs as gifts. Lewis was also instructed to invite the chiefs to Washington to meet Jefferson.

The Louisiana Purchase

As Jefferson and Lewis fleshed out the details of the plan, they were intent on keeping the expedition small, so it would not draw the attention of French authorities. Once the Louisiana Purchase was finalized, the United States controlled roughly two-thirds of the territory the expedition needed to pass through, and the French issue was resolved. Still, they would need to take into account the Indian Tribes and French and British frontiersmen who hunted and trapped in the region.

William Clark

As the scope and details of the expedition expanded, it required more men — and more leadership. Lewis asked his friend, 32-year-old William Clark, to join the project and lead it with him.  Clark was responsible for hiring and training the men for the expedition, and his skills as a cartographer and surveyor were immensely valuable.

Throughout the course of the expedition, Clark’s rank was Second Lieutenant, which officially made him second-in-command, but as far as Lewis was concerned, they were co-commanders of the expedition, which they came to call the Corps of Discovery. 

Like Lewis, Clark had experience on the frontier and had served under Wayne in the Northwest Indian War. He was also the younger brother of George Rogers Clark.

Governor William Clark, Lewis and Clark Expedition
William Clark. Image Source: Wikipedia.

Preparations for the Expedition

Before the expedition officially launched, Lewis and Clark spent a significant amount of time educating themselves, gathering supplies, and recruiting men. They rarely worked together and were often in different parts of the country completing the necessary tasks. 

The mission had the full support of the Secretary of War, Harry Dearborn, so they were able to choose just about any soldier they wanted for the trip. Clark recruited and trained men from Ohio, Kentucky, and Illinois. 

Lewis also spent time with some of the scientific and medical experts of the day, learning about botany, zoology, celestial navigation, and medicine. Some of the men he learned from were Founding Father Doctor Benjamin Rush and German-American physician Caspar Wistar — who taught him about fossils.

Lewis had boats built in Pittsburgh and gathered supplies at Harpers Ferry. He then left Pittsburgh on August 31, 1803, and traveled down the Ohio River to join up with Clark and his recruits at Louisville, Kentucky.

The Lewis and Clark Expedition Begins

The expedition, consisting of around 40 men, set out on its journey on May 14, 1804, starting at the confluence of the Mississippi and Missouri Rivers near St. Louis, Missouri. They traveled northwest along the Missouri River.

Joining Lewis and Clark were boatmen to steer their keelboat and two pirogues — smaller boats — along with soldiers, and frontiersmen who served as scouts and hunters. One of the men Clark recruited in Kentucky was Private John Colter. Colter would go on to become of the most famous Mountain Men in American history and is known for being one of the first Anglo-Americans to lay eyes on present-day Yellowstone National Park.

They packed a wide range of equipment for their trip, including rifles, food, warm clothing, and glass beads and trinkets to trade with the Indian Tribes they would encounter along the way.

The expedition moved slowly, covering as few as 5 miles a day and as many as 20 miles a day. Clark often stayed in a boat and Lewis walked along the shore. 

Death of Charles Floyd

On August 20, 1804, the Expedition suffered its first — and only death — when Sergeant Charles Floyd died from what is believed to have been appendicitis

Fort Mandan — the First Winter

In mid-October 1804, they reached the Mandan villages located near present-day Washburn, North Dakota. The villages were large settlements where around 5,000 people lived. The villages were an important trade center in the region, where French frontiersmen and Indians me to trade. Lewis and Clark decided to spend the winter near the villages, which turned out to be a key decision that contributed to the success of their journey. The members of the expedition built a log fort called Fort Mandan to live in for the winter. During the winter, the expedition established good relations with the Mandans and received valuable information about the best route to head west to the Pacific Ocean. 

Lewis and Clark Expedition, Meeting Mandan Tribe
This painting depicts Lewis and Clark meeting members of the Mandan Tribe. Image Source: Wikipedia.

Sacagawea’s Contribution to the Expedition

While they were at Fort Mandan, they met a French-Canadian fur trapper and trader named Touissant Charbonneau and his wife Sacagawea. She was a Shoshone girl, just 15 years old, and pregnant. Her tribal homeland was in the Rocky Mountain country far to the west of Fort Mandan, and she spoke both the Shoshone and Minitari dialects. 

Lewis and Clark decided to hire both Charbonneau and Sacagawea as guides and interpreters for the next leg of the journey. Their son Jean-Baptiste, known as “Little Pomp”, by the other members of the expedition, was born in February and accompanied his parents on the journey west and back to Fort Mandan the following year.

Sacagawea’s knowledge of the western territory, the Indian Tribes, and her language skills played an important role in the success of the expedition. At times, she served as a peacemaker and she helped negotiate for valuable necessities like horses and supplies. She even showed the Americans edible plants. Most accounts agree that she was an invaluable member of the team and that without her the expedition may very well have failed.

Pacific Coast

In the spring, the expedition continued up the Missouri River and into Montana Territory. They believed the Missouri River would connect to another great river, which would flow to the Pacific. However, they found there was no river and as they neared the Rocky Mountains they were forced to travel on land. 

They traveled across much of present-day Northern Idaho until they arrived at the Clearwater and Snake Rivers, where they could use their boats again. In mid-October 1805, they reached the Columbia River. Soon after — and 18 months after they left St. Louis — Lewis saw Mount Hood in the distance. They continued moving west and built a fort to stay in for the winter, which they called Fort Clatsop.

Fort Clatsop

The fort was located It was located near present-day Astoria, Oregon. The members of the expedition spent the winter preparing for the trip home by boiling salt from the ocean and hunting elk and other wildlife. The expedition left Fort Clatsop on March 23, 1806.

Mount Hood, From the Columbia River, Lewis and Clark Expedition
This illustration depicts Mount Hood as seen from the Columbia River. Image Source: New York Public Library Digital Collections.

Return to St. Louis

On the way back to St. Louis, the expedition split up into two groups. Clark led one group up the Yellowstone River, while Lewis led another group into North Central Montana and the Province of Alberta. In August, they met on the Missouri River and arrived back in St. Louis on September 23, 1806. It was nearly two-and-a-half years since their journey started. They traveled over 7,000 miles and completed one of the most significant and ambitious explorations of the American West.

Outcome of the Expedition

The members of the expedition kept journals and documented many aspects of their long journey. They recorded just about everything they observed, including 178 plant species and 122 animal species.

They also documented their experiences with the 50 Indian Tribes they came into contact with — nearly half of which had never seen a white person before.

After the expedition, Lewis was appointed Governor of the Louisiana Territory, but he died a few years later. Clark became governor of the Missouri Territory and the Superintendent of Indian Affairs.

In 1807, John Colter joined the Missouri Fur Company and went on an expedition to the Rocky Mountains. The expedition established Fort Raymond in present-day Wyoming, and Colter was sent out to contact local Indian Tribes to establish trade relations. It is believed Colter traveled 500 miles during the winter of 1807–1808. During the journey, he is believed to have been the first white man to see present-day Jackson’s Hole and Yellowstone Lake. Afterward, he told stories of the wonders he had seen, including hot springs and fumaroles — vents in the surface that vent sulfurous gasses — which would later become known as “Colter’s Hell.”

Lewis and Clark Expedition Significance

The Lewis and Clark Expedition was a significant event in United States history, as it opened up the western territories to American expansion and launched America’s belief in its Manifest Destiny. It was also a remarkable achievement for its time, as no American was fully aware of what awaited them in the American West. It will always be remembered as one of the most important and historic events in the history of the nation.

Interesting Facts About the Lewis and Clark Expedition

  1. The Lewis and Clark Expedition was the first American expedition to cross the western portion of the United States.
  2. In all, the expedition traveled over 7,000 miles and took more than two and a half years to complete.
  3. The maps that were made collected helped open the western territories to American settlers.
  4. The information that was collected provided valuable information on the natural resources, Indian Tribes, and the geography of the territory. The information was used to create the first comprehensive study of the natural history of the American West
  5. The expedition also paved the way for future explorers, traders, and settlers, including Zebulon Pike, the various Mountain Men, such as Jim Bridger, and emigrant groups such as the Donner Party and the Mormons.
Thomas Jefferson, Painting, Rembrandt Peale
Thomas Jefferson. Image Source: Wikipedia.

Lewis and Clark Expedition APUSH Study Guide

Use the following links and videos to study the Lewis and Clark Expedition and Manifest Destiny for the APUSH Exam. Also, be sure to look at our Guide to the AP US History Exam.

Lewis and Clark Expedition APUSH Definition

The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was a mission commissioned by President Thomas Jefferson in 1803 to explore and map the newly acquired western territory of the United States. Led by Captain Meriwether Lewis and Second Lieutenant William Clark, the expedition set out to find a practical route across the western half of the continent, as well as establish an American presence in the region and study the area’s plants, animals, and geography. The expedition, which lasted from May 1804 to September 1806, was a major achievement in American history, as it opened up the West to further exploration and settlement and provided valuable scientific and geographic information about the American West.

Lewis and Clark Expedition APUSH Video

This video provides a look at the story of the Lewis and Clark Expedition, which explored the Louisiana Purchase.

Citation Information

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  • Article Title The Lewis and Clark Expedition
  • Date May 14, 1804–September 23, 1806
  • Author
  • Keywords Lewis and Clark Expedition, Meriwether Lewis, William Clark, Thomas Jefferson, John Colter, Sacagawea
  • Website Name American History Central
  • Access Date May 27, 2024
  • Publisher R.Squared Communications, LLC
  • Original Published Date
  • Date of Last Update December 14, 2023