"Left Pittsburgh this day at 11 o'clock with a party of 11 hands 7 of which are soldiers, a pilot and three young men on trial they having proposed to go with me throughout the voyage." With those words, written on August 31, 1803, Meriwether Lewis began his first journal entry on the epic Lewis and Clark Expedition to the Pacific Ocean.

 Lewis declared the mouth of the river Dubois (on the east side of the Mississippi across from the mouth of the Missouri river) to be the expedition's official point of departure, but the two and one-half months spent descending the Ohio River can be considered its real beginning.

 Clark made most of the preparations, by way of letters to Jefferson. He bought two large buckets and five smaller buckets of salt, a ton of dried pork, and medicines.

Reconstruction of Camp Dubois, Lewis and Clark State Historic Site, Illinois

 The party of 33 included 29 individuals who were active participants in the Corps' organizational development, recruitment and training at its 1803–1804 winter staging area at Camp Dubois, Illinois Territory. They then departed from Camp Dubois, near present day Hartford, Illinois, and began their historic journey on May 14, 1804. They soon met up with Lewis in Saint Charles, Missouri, and the corps followed the Missouri River westward. Soon they passed La Charrette, the last white settlement on the Missouri River. The expedition followed the Missouri through what is now Kansas City, Missouri, and Omaha, Nebraska. On August 20, 1804, the Corps of Discovery suffered its only death when Sergeant Charles Floyd died, apparently from acute appendicitis. He was buried at Floyd's Bluff, near what is now Sioux City, Iowa. During the final week of August, Lewis and Clark had reached the edge of the Great Plains, a place abounding with elk, deer, bison, and beavers. They were also entering Sioux territory.

 The first tribe of Sioux they met, the Yankton Sioux, were more peaceful than their neighbors further west along the Missouri River, the Teton Sioux, also known as the Lakota. The Yankton Sioux were disappointed by the gifts they received from Lewis and Clark—five medals—and gave the explorers a warning about the upriver Teton Sioux. The Teton Sioux received their gifts with ill-disguised hostility. One chief demanded a boat from Lewis and Clark as the price to be paid for passage through their territory. As the Indians became more dangerous, Lewis and Clark prepared to fight back. At the last moment before

fighting began, the two sides fell back. The Americans quickly continued westward (upriver) until winter stopped them at the Mandan tribe's territory.

Reconstruction of Fort Mandan, Lewis & Clark Memorial Park, North Dakota

 In the winter of 1804–05, the party built Fort Mandan, near present-day Washburn, North Dakota. Over the course of the winter the expedition enjoyed generally good relations with the Mandan Indian tribe who lived alongside the Fort. It was at Fort Mandan that Lewis and Clark came to employ a French-Canadian fur trapper named Toussaint Charbonneau, whose young Shoshone Indian wife, Sacagawea, (pronounced Sa-ka-ga-wea) translated for the expedition among the Shoshone and Nez Perce. In a few instances, Sacagawea also managed to serve as a guide for the expedition.

 Black-tailed Prairie Dog

In April 1805, some members of the expedition were sent back home from Mandan in the 'return party'. Along with them went a report about what Lewis and Clark had discovered, 108 botanical and zoological specimens (including some living animals), 68 mineral specimens, and Clark's map of the United States. Other specimens were sent back to Jefferson periodically, including a prairie dog which Jefferson received alive in a box.

 The expedition continued to follow the Missouri to its headwaters and over the Continental Divide at Lemhi Pass via horses. In canoes, they descended the mountains by the Clearwater River, the Snake River, and the Columbia River, past Celilo Falls and past what is now Portland, Oregon. At this point, Lewis spotted Mount Hood, a mountain known to be very close to the ocean. On a big pine, Clark carved

 Clark had written in his journal, "Ocian in view! O! The Joy!". One journal entry is captioned "Cape Disappointment at the Entrance of the Columbia River into the Great South Sea or Pacific Ocean".By that time the expedition faced its second bitter winter during the trip, so the group decided to vote on whether to camp on the north or south side of the Columbia River. The party agreed to camp on the south side of the river (modern Astoria, Oregon), building Fort Clatsop as their winter quarters. While wintering at the fort, the men prepared for the trip home by boiling salt from the ocean, hunting elk and other wildlife, and interacting with the native tribes. The 1805–06 winter was very rainy, and the men had a hard time finding suitable meat. They never consumed much Pacific salmon because the fish only return to the rivers to spawn in the summer months.

 The explorers began their journey home on March 23, 1806. On the way home, Lewis and Clark used four dugout canoes they bought from the Native Americans, plus one that they stole in "retaliation" for a previous theft. Less than a month after leaving Fort Clatsop, they abandoned their canoes because portaging around all the falls proved terribly difficult.

 On July 3, after crossing the Continental Divide, the Corps split into two teams so Lewis could explore the Marias River. Lewis' group of four met some Blackfeet Indians. Their meeting was cordial, but during the night, the Blackfeet tried to steal their weapons. In the struggle, two Indians were killed, the only native deaths attributable to the expedition. The group of four: Lewis, Drouillard, and the Field brothers, fled over 100 miles (160 km) in a day before they camped again. Clark, meanwhile, had entered Crow territory. The Crow tribe were known as horse thieves. At night, half of Clark's horses were gone, but not a single Crow was seen. Lewis and Clark stayed separated until they reached the confluence of the Yellowstone and Missouri Rivers on August 11. Clark's team had floated down the rivers in bull boats. While reuniting, one of Clark's hunters, Pierre Cruzatte, blind in one eye and nearsighted in the other, mistook Lewis for an elk and fired, injuring Lewis in the thigh. Once reunited, the Corps was able to return home quickly via the Missouri River. They reached St. Louis on September 23, 1806.

 The Corps of Discovery returned with important information about the new United States territory and the people who lived in it, as well as its rivers and mountains, plants and animals. The expedition made a major contribution to mapping the North American continent.