After the Louisiana Purchase of 1803, Thomas Jefferson selected Meriwether Lewis to lead an expedition to explore the wilderness, Indians, botany, and geology of the new lands acquired in the deal. Lewis selected William Clark to help him in this colossal effort. The expedition became known as the Corps of Discovery. Little did they know, that this adventure would become one of the most storied in American history.

On May 14, 1804, the historic journey began, as Lewis, Clark, and 38 other Corps members sailed from St. Charles, Missouri, west on the Missouri River. Averaging about 20 miles of distance per day, the Corps sailed past La Charette, the last White settlement on the Missouri River on May 25. On July 4, the Corps celebrated the first Independence Day spent west of the Mississippi River by firing their keelboat cannon and naming a creek (near present day Atchison, Kansas) Independence Creek.

On August 3, 1804, the Corps encountered Indians for the first time near present day Omaha, Nebraska. The Indians were presented with such gifts as peace medals and flags and told of a "Great Father to the East" that would ensure their prosperity provided they didn't attack White settlers. On August 20, the Corps experienced their first and only death when Charles Floyd died of a burst appendix. Nevertheless, the expedition continued. As the Corps entered the Great Plains, new animals previously unknown such as coyote and antelope were recorded. As the Corps sailed north, they met up with the Teton Sioux Indians. Near present-day Pierre, South Dakota, the Teton Sioux ( Lakota) demanded one of their boats as a toll for moving farther upriver. A fight nearly ensued, but was defused by the diplomacy of a chief named Black Buffalo. For three more anxious days, the expedition stayed with the tribe.

On October 24, the Corps reached the villages of the Mandan Indians near present-day Bismarck, North Dakota. The villages were huge, and contained more people than many major cities in America. Lewis and Clark decided to build a fort, which they named Fort Mandan, across the river from the Indian villages. Communication was constantly an issue between the Corps of Discovery and local Indian tribes. For this reason, Lewis and Clark hired Toussaint Charbonneau, a French-Canadian fur-trapper and his wife, Sacagawea, to translate for them when they headed west toward the mountains.