U.S. President Thomas Jefferson sends a secret message to Congress asking for approval and funding of an expedition to explore the Western part of the continent.
Meriwether Lewis begins his training as the expedition's leader in Philadelphia.
July 4, 1803
News of the Louisiana Purchase is announced; Lewis will now be exploring land largely owned by the United States.
In Pittsburgh, Lewis oversees construction of a keelboat, then picks up William Clark and other recruits as he travels down the Ohio River.
Lewis and Clark establish Camp Wood, the winter camp for their Corps of Discovery, on the Wood River in Illinois.
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.
The Corps attends a Mandan buffalo dance, performed to call buffalo to the area.
February 11, 1805
Sacagawea's son, Jean Baptiste Charbonneau—nicknamed Pompy by Clark—is born with assistance from Lewis.
April 7, 1805
Lewis and Clark send a shipment of artifacts and specimens to President Jefferson; the "Permanent Party" heads west.
April 29, 1805
The Corps marvels at the abundance of game; they kill their first grizzly bear near the Yellowstone River in Montana.
May 16, 1805
One of their boats nearly overturns and Lewis credits Sacagawea with saving their most important possessions.
May 31, 1805
The Corps reaches the White Cliffs region of the Missouri River.
June 1, 1805
The Corps reaches an unknown fork in the Missouri and must determine which branch to choose.
June 13, 1805
Lewis reaches the Great Falls of the Missouri—five massive cascades around which the men must carry all of their gear, including the canoes.
Late July 1805
The expedition reaches the Three Forks of the Missouri which they name the Jefferson, Gallatin, and Madison in honor of the President, Secretary of the Treasury, and Secretary of State.
August 8, 1805
Sacagawea recognizes Beaverhead Rock and knows they are close to Shoshone lands.
August 12, 1805
Jefferson receives the shipment from Fort Mandan; Lewis finds the headwaters of the Missouri River, then crosses the Continental Divide and Lemhi Pass to discover that there is no Northwest Passage.
August 17, 1805
The main party arrives at the Shoshone camp, where Sacagawea recognizes the chief as her long-lost brother, Cameahwait.
August 18, 1805
Lewis' celebrates his 31st birthday and vows "in future, to live for mankind as I have heretofore lived only for myself."
August 31, 1805
The expedition sets out for the Bitterroot Mountains with many horses and a mule acquired from the Shoshone.
September 9, 1805
The men camp near today's Missoula, Montana at a spot they name Traveler's Rest while they prepare for the mountain crossing to come.
September 11, 1805
The Corps begins the steep ascent into the Bitterroot Range of the Rocky Mountains; the crossing will cover more than 160 miles (260 kilometers).
September 23, 1805
Starving, the men emerge from the mountains near present-day Weippe, Idaho, at the villages of the Nez Perce Indians.
October 7, 1805
After learning a new method to make dugout canoes from the Nez Perce, the men push off down the Clearwater River near Orofino, Idaho; it is the first time they've traveled with the current at their back in almost two years.
October 16, 1805
The expedition reaches the Columbia River, the last waterway to the Pacific Ocean.
Late October 1805
The Corps must run their canoes through treacherous rapids at The Dalles and Celilo Falls.
November 7, 1805
Believing he sees the Pacific, Clark writes, "Ocean in View! O the joy." In reality, they are seeing only the widening estuary of the Columbia River.
November 24, 1805
Having reached the Pacific, the entire expedition—including Sacagawea and Clark's slave, York—take a vote on where to build their winter quarters. They chose the Clatsop Indian side of the Columbia, and the encampment came to be called Fort Clatsop.
March 23, 1806
After a winter of only 12 days without rain, the men present their fort to the Clatsop Indians and set out for home.
September 23, 1806
Having found an easier route across the country, the men reach St. Louis nearly two and a half years after their journey began and are acclaimed as national heroes.