After Lewis returned to Washington from Philadelphia in the summer of 1803, the United States' purchase of the Louisiana territory from France was announced. Now the journey was even more important. Lewis and his party would be exploring land that belonged to the United States. Armed with Jefferson's letter of instructions, Lewis traveled to Pittsburgh and then set out on the Ohio River. At Clarksville, in present-day Indiana, he met up with William Clark. They packed the keelboat, which Lewis had designed, and two pirogues (canoe-like boats) with supplies and headed downriver. They were accompanied by some recruited soldiers, Clark's African-American slave York, and Lewis's Newfoundland dog Seaman.
Lewis and Clark spent the winter of 1803-04 at Camp Dubois on the east bank of the Mississippi River, upstream from St. Louis. Here the captains recruited more men, increasing the ranks of the "Corps of Volunteers for Northwest Discovery" to more than 40. As spring approached, the members of the Expedition gathered food and supplies and packed them into barrels, bags, and boxes. The boats were loaded and the party made ready to depart. On May 14, 1804, the Lewis & Clark Expedition began its trip up the Missouri River.
Lewis, Clark, and other members of the Expedition began writing in their journals, a practice that continued throughout the journey. Map-making was equally important, particularly in the previously unexplored regions. As the explorers encountered new rivers and streams, they were responsible for naming them. They named some for famous Americans, such as Jefferson and James Madison, and others for friends and members of the Expedition. The same was true for some of the new plants and animals they encountered. Many of these names are still in use today.
In late July the explorers camped north of the mouth of the Platte River, at a site they called Council Bluff. Lewis noted in his journal that the location was good for a trading post. It was here on August 3 that Lewis and Clark had their first council with Native Americans, a small group of Oto and Missouri Indians. During this time Sergeant Charles Floyd, one of the soldiers, became ill and died of a ruptured appendix on August 20. He was the only member of the Expedition to die during the journey.
As the Expedition traveled up the Missouri River during late August and into September, the landscape along the river changed drastically. The forests receded, replaced first by tall prairie grass and then the shorter grass of the high plains. Thousands of buffalo were seen grazing, and prairie dogs were first sighted. The evening temperatures became colder, with frost on the ground some mornings. Lewis and Clark planned to winter near long-established villages inhabited by large numbers of the Mandan and Hidatsa tribes, north of present-day Bismarck, North Dakota. On October 26, 1804, the Expedition arrived at the earth-lodge Indian villages, approximately 1,600 miles from Camp Dubois. A good site was found for a camp, and the men set about building Fort Mandan across the river from the Indian villages.
During the winter Lewis and Clark worked to establish good relations with the Indians, who had been dealing with English and French-Canadian traders for some time. One of these traders, Toussaint Charbonneau, was persuaded to accompany the Expedition as an interpreter when it left in the spring. His young pregnant wife, Sacagawea, who had been captured from her Lemhi Shoshone tribe years before by Hidatsas, was to go along as well. Sacagawea thus became the only female member of the Expedition. Her baby, named Jean Baptiste, was born on February 11, 1805. Lewis and Clark realized Sacagawea would be useful as a guide as the Expedition proceeded west, and believed the presence of the woman and her child would signal that the party was a peaceful one.
During the cold winter at Fort Mandan, the members of the Expedition prepared a shipment that was to be sent back to President Jefferson. The shipment included maps, written reports, items made by Native Americans, the skins and skeletons of previously unknown animals, soil samples, minerals, seeds, and cages containing a live prairie dog, a sharp-tailed grouse, and magpies. The large keelboat and about a dozen men were dispatched downriver on April 7. The shipment was received at the President's House in Washington four months later. Many of these items, including a painted Mandan buffalo robe, were eventually put on display in Jefferson's "Indian Hall," the entrance hall of Monticello, his home near Charlottesville, Virginia. Other objects were later displayed in Charles Willson Peale's museum in Philadelphia. The same day the shipment was sent downriver, the "permanent party" of the Expedition left Fort Mandan in the two pirogues and six dugout canoes and headed westward into uncharted territory.
Proceeding into present-day Montana, the explorers were amazed by herds of buffalo numbering more than 10,000 and by the ferocity of grizzly bears. On June 13, more than two months after leaving Fort Mandan, the Expedition reached the Great Falls of the Missouri River, one of the greatest natural obstacles it would face. The falls gave off a thunderous roar, which emanated from a 10-mile stretch of river that dropped more than 400 feet over five cascades. The members of the Expedition unloaded the supplies from the boats and undertook a difficult overland portage around the falls.
In late July, the Expedition reached the Three Forks of the Missouri River then headed southwest, up the shallow, swift stream they named the Jefferson River. Sacagawea recognized Beaverhead Rock (north of present-day Dillon, Montana) and said the party was near the home of her people, the Shoshone. Desperate to find the Indians and their horses, Lewis decided to scout ahead with three men. On August 12, Lewis ascended the final ridge to the Continental Divide on the Lemhi Pass (on the present-day border between Montana and Idaho). From the summit he expected to see plains with a large river flowing to the Pacific Ocean. But when he reached the peak and looked west, he came to the realization that there was no water route to the Pacific Ocean, only more mountains.
A few days later, Lewis came upon a Shoshone village and tried to negotiate for horses needed to cross the daunting mountains. Clark and the rest of the Expedition arrived and Sacagawea was brought in to help translate. She was reunited with her brother, Cameahwait, the Shoshone chief. The explorers set up camp near the Indian village and named it Camp Fortunate. The Shoshones provided the Expedition with some horses, a guide named Old Toby who had traveled through the mountains before, and information about mountain trails and other Indian tribes the explorers might encounter. The entire Expedition proceeded through the Lemhi Pass and made camp along a creek. This camp was called Traveler's Rest.
Even though winter was fast approaching and snow was covering some of the peaks, Lewis and Clark decided to continue on through the Bitterroots, a range of the Rocky Mountains. Cameahwait had told them of a trail (Lolo Trail) used by the Nez Perce, a tribe that lived west of the mountains. Unfortunately, the Expedition failed to locate this trail and spent many more days in the treacherous mountains than necessary. Temperatures dropped below freezing and the trail was steep and rocky. The men were fatigued and food supplies were low, but the Expedition succeeded in making it across the mountains. Once out of the Bitterroots, the explorers made canoes using the Indian method of burning out the inside of logs. Game was still scarce, so Lewis and Clark purchased roots, fish, and dogs from the Nez Perce.
On October 7, the Expedition put five new canoes into the Clearwater River and, for the first time since leaving St. Louis, paddled downstream. The party went down the Clearwater and Snake Rivers to the Columbia River, which the explorers knew flowed into the Pacific Ocean. By the end of October the Expedition had made its way around the falls of the Columbia and sighted Mount Hood. In November the Pacific Ocean was sighted. Clark estimated in his journal that the party had traveled 4,162 miles from the mouth of the Missouri River.
By Christmas, the men had nearly finished their winter quarters, which they called Fort Clatsop after the local Indian tribe. The explorers spent the cold, rainy, generally miserable winter updating their journals, trading with the Indians for food and other needed items, and preparing for the long return journey.
On March 23, 1806, Lewis and Clark presented Fort Clatsop to Chief Coboway (a Clatsop Indian) and the Expedition began its trek home. The party reached the Nez Perce lands in May but had to wait there until late June for the snows to melt on the Bitterroots. Once it crossed the mountains and reached Traveler's Rest, the Expedition split up. Lewis took part of the men north and Clark led a party down the Yellowstone River. On July 26, Lewis and his men become engaged in a fight with Blackfeet warriors, who were attempting to take horses and guns. Two of the warriors were killed. On August 12, the entire Expedition was reunited at the point where the Yellowstone flows into the Missouri River.
Traveling with the Missouri's current, the Expedition was able to cover up to 70 miles in a day. The explorers reached the Mandan villages on August 14, and there parted company with Charbonneau, Sacagawea, and young Jean Baptiste. The Expedition finished its journey when it reached St. Louis on September 23, 1806. President Jefferson had thought that the men would be gone for about a year, and consequently had feared for their safety. In fact, it took the Lewis and Clark Expedition two years, four months, and nine days to travel across the western part of the continent and back.
President Jefferson's instructions to Lewis were so extensive as to be almost impossible to fulfill, yet he viewed the Expedition as a tremendous success. The discoveries made by the explorers changed the vision of this young country. No water route to the Pacific was found, but accurate and detailed maps were drawn. Peaceful contact was made with Native American tribes and trade was discussed. The body of knowledge added to the scientific community proved to be truly invaluable and vast reaches of North America had been explored. Lewis and Clark's "voyage of discovery" turned out to be one of Thomas Jefferson's most enduring legacies.