Lewis and Clark Expedition (1804-1806): Crossing a Continent

The Lewis and Clark Expedition was a United States Army expedition that travelled from the Mississippi River to the Pacific Ocean and back between May 1804 and September 1806. Led by Meriwether Lewis and William Clark and sent by President Thomas Jefferson, the small Corps of Discovery mapped the Missouri and Columbia river routes, met dozens of Native nations and recorded a wealth of scientific information about lands most Americans had never seen.

Background: Jefferson’s western ambitions

Jefferson had long been interested in the American West. In January 1803 he sent a confidential message to Congress requesting 2,500 dollars to fund an expedition up the Missouri River, officially to promote trade with Native peoples. Within months the Louisiana Purchase gave the United States a claim to the entire Missouri basin, turning the venture into a survey of new national territory.

Jefferson chose his private secretary, Meriwether Lewis, an army captain from Virginia, to lead it. Lewis invited William Clark, a former army officer under whom he had served, to share command. Although the War Department gave Clark only the rank of lieutenant, Lewis treated him as an equal co-captain throughout the journey.

Lewis prepared carefully. He studied botany, astronomy, medicine and map-making with leading scientists in Philadelphia and gathered supplies including scientific instruments, medicines, rifles and large quantities of gifts such as beads, cloth and peace medals for Native leaders.

Up the Missouri to the Mandan villages

The Corps spent the winter of 1803–1804 training at Camp Dubois, on the Illinois side of the Mississippi opposite the mouth of the Missouri. On 14 May 1804 it set out upriver in a 55-foot keelboat and two smaller boats called pirogues. The permanent party eventually numbered about 33 people, including soldiers, civilian boatmen and interpreters, and York, a man enslaved by Clark.

Progress against the Missouri’s strong current was slow and exhausting. In August 1804, near present-day Sioux City, Iowa, Sergeant Charles Floyd died, probably of a ruptured appendix. He was the only member of the expedition to die during the journey. In councils with the Otoe, Missouria and Yankton Sioux, the captains announced that the United States now claimed sovereignty and distributed medals and gifts.

In late September 1804, near present-day Pierre, South Dakota, a tense confrontation with the Teton (Lakota) Sioux, who controlled river trade in the area, nearly ended in violence before both sides stepped back.

By late October the expedition reached the earth-lodge villages of the Mandan and Hidatsa, a major trading centre on the upper Missouri in present-day North Dakota. The Corps built Fort Mandan and spent the winter there, gathering information about the lands ahead from their hosts.

There the captains hired Toussaint Charbonneau, a French-Canadian trader, as an interpreter, together with his young wife Sacagawea, a Lemhi Shoshone woman who had been captured by Hidatsa raiders as a girl. In February 1805 she gave birth to a son, Jean Baptiste, who travelled with the expedition as a baby. In April 1805 the keelboat returned downriver carrying maps, reports and specimens for Jefferson, including a live prairie dog.

Across the Rocky Mountains

The remaining party continued west in canoes and pirogues. In June 1805 they reached the Great Falls of the Missouri in present-day Montana, where carrying the boats and supplies around a series of waterfalls took about a month. At the Three Forks of the Missouri, Sacagawea recognised the place where she had been captured years earlier.

On 12 August 1805 Lewis crossed the Continental Divide at Lemhi Pass. The expedition urgently needed horses to cross the mountains, and in a remarkable coincidence the Shoshone chief Cameahwait proved to be Sacagawea’s brother. The Shoshone traded horses and provided a guide, known to the explorers as Old Toby.

The crossing of the Bitterroot Mountains on the Lolo Trail in September 1805 was the hardest part of the journey. Snow, steep terrain and lack of game brought the men close to starvation, and they killed some of their horses for food. They emerged on the Weippe Prairie, where the Nez Perce gave them food, helped them build canoes and cared for their horses until their return.

To the Pacific and back

The Corps paddled down the Clearwater, Snake and Columbia rivers, passing the great fishing grounds and rapids of the Columbia, including Celilo Falls. In early November 1805 they reached the wide estuary of the Columbia, and Clark wrote in his journal that the ocean was in view, though they were still some miles from the open sea.

To decide where to spend the winter, the captains put the question to the whole party in late November 1805. York and Sacagawea were included in the vote, an unusual step for the time. The group built Fort Clatsop near present-day Astoria, Oregon, and endured a damp, rainy winter, trading with the Clatsop and Chinook peoples.

The return journey began on 23 March 1806. After recrossing the mountains, the captains split up in July to explore more territory. Lewis’s small party had a violent encounter with a group of Blackfeet near the Two Medicine River on 27 July 1806, in which two Blackfeet men were killed. In August Lewis was accidentally shot through the thigh by one of his own men, Pierre Cruzatte, who mistook him for an elk. The reunited Corps sped down the Missouri and arrived in St. Louis on 23 September 1806, long after many had given them up for dead.

Key people

• Meriwether Lewis (1774–1809), co-leader and the expedition’s naturalist; he later became governor of Louisiana Territory and died of gunshot wounds in Tennessee in 1809, probably by suicide.
• William Clark (1770–1838), co-leader and chief map-maker, later a long-serving superintendent of Indian affairs at St. Louis.
• Sacagawea (c. 1788–1812 or later), Lemhi Shoshone interpreter and guide; the date of her death is debated.
• York (c. 1770 – before 1832), enslaved by Clark, who did the same work as the soldiers but was refused his freedom for years afterwards.
• Thomas Jefferson (1743–1826), the president who conceived and sponsored the expedition.

Scientific and political legacy

The expedition’s journals are among the most important documents of early American history. The captains and several sergeants kept detailed records describing landscapes, weather, Native customs and wildlife. Historians commonly credit the expedition with describing around 178 plants and 122 animals that were new to Western science, among them the grizzly bear, the pronghorn and the coyote.

Clark’s maps transformed knowledge of western geography, showing for the first time the true width of the Rocky Mountains. They also proved that there was no easy all-water route across the continent, ending a hope that had driven European exploration for centuries. A version of his map was published in 1814 with the first account of the journey.

Politically, the expedition strengthened the American claim to the Pacific Northwest and encouraged the fur trade. Within decades, traders, missionaries and settlers followed, many travelling on the Oregon Trail. For the Native nations the explorers met, the expedition was the start of a period of growing American power that brought disease, loss of land and forced relocation.

Myths and facts

Myth: Sacagawea guided the expedition across the continent. She was an important interpreter and recognised landmarks in her homeland, but she did not know most of the route. Her greatest contributions were helping obtain Shoshone horses and showing other nations, by her presence with a baby, that the party was peaceful.

Myth: The explorers discovered an unknown land. Every region they crossed was home to Native peoples who knew it intimately, and the explorers depended on their food, horses, maps and advice. Fur traders had also already visited the upper Missouri and the Columbia’s mouth.

Myth: Many of the Corps died on the journey. Only one member, Sergeant Floyd, died, which reflects good leadership and a great deal of help from Native communities.

By the numbers

Timeline

• 1803, 18 January: Jefferson asks Congress to fund an expedition up the Missouri.
• 1804, 14 May: The Corps of Discovery leaves Camp Dubois.
• 1804, 20 August: Sergeant Charles Floyd dies near present-day Sioux City.
• 1804, October–November: The Corps reaches the Mandan villages and builds Fort Mandan.
• 1805, 7 April: The expedition leaves Fort Mandan heading west.
• 1805, 12 August: Lewis crosses the Continental Divide at Lemhi Pass.
• 1805, November: The Corps reaches the Columbia estuary and builds Fort Clatsop.
• 1806, 23 March: The return journey begins.
• 1806, 23 September: The expedition arrives back in St. Louis.

Why it matters

The Lewis and Clark Expedition turned a vaguely understood territory into mapped, described land claimed by the United States. Its journals remain a key source for the natural history and Native peoples of the West in the early nineteenth century, and its story, including the roles of Sacagawea and York, continues to shape how Americans remember the nation’s westward expansion and its costs.