March 10, 1804
Lewis and Clark travel to St. Louis to attend ceremonies formally transferring the Louisiana Territory to the United States.
May 14, 1804
The Corps of Discovery leaves Camp Wood and begins its journey up the Missouri River "under a gentle breeze."
July 4, 1804
The Corps holds the first Independence Day celebration west of the Mississippi River.
August 3, 1804
North of present-day Omaha, Nebraska, the Corps holds a council with the Oto and Missouri Indians.
August 20, 1804
Sergeant Charles Floyd dies of natural causes near present-day Sioux City, Iowa; he will be the only fatality among the Corps of Discovery during the expedition.
August 30, 1804
The Corps holds a council with the Yankton Sioux at present-day Yankton, South Dakota.
Early September 1804
The Corps enters the Great Plains and sees animals unknown in the eastern United States.
September 25, 1804
The Corps has a tense encounter with the Teton Sioux near today's Pierre, South Dakota; one of the Sioux chiefs waves his men off and conflict is averted.
October 24, 1804
Near today's Bismarck, North Dakota, the Corps arrives at the villages of the Mandan and Hidatsa, buffalo-hunting tribes that live along the Missouri River.
November 4, 1804
Lewis and Clark hire French-Canadian fur-trader Toussaint Charbonneau and his Shoshone wife, Sacagawea, to act as interpreters on the journey ahead.
December 17, 1804
The men record the temperature at 45 degrees below zero, "colder than [they] ever knew it to be in the States."
December 24, 1804
The men finish building Fort Mandan, their winter quarters in present-day North Dakota.