| Thomas Jefferson becomes President. | | |
| Secret communication to Congress. | | |
| Lewis is sent to Philadelphia for instruction and starts buying supplies to outfit the expedition. | | |
| Lewis offers shared command to Clark, who accepts. | | |
| News of Louisiana Purchase announced. | | |
| Lewis oversees construction of a big keelboat in Pittsburgh, then takes it down Ohio River, picking up Clark and some recruits along the way. | | |
| Expedition establishes Camp Wood (also called Camp Dubois) on east bank of Mississippi, upstream from St. Louis. | | |
| Lewis and Clark attend ceremonies in St. Louis formally transferring Louisiana Territory from France to United States. | | |
| Expedition sets off from Camp Dubois “under a jentle brease,” Clark writes. | | |
| Expedition passes La Charette, “the last settlement of whites on this river.” | | |
| First official council between representatives of United States and western Indians. | | |
| Sergeant Charles Floyd becomes the expedition’s first casualty from what was probably a burst appendix. | | |
| Expedition holds friendly council with Yankton Sioux | | |
| Moving into the Great Plains, the expedition begins seeing animals unknown in the East. On this particular day, all the men are employed drowning a prairie dog out of its hole for shipment back to Jefferson. | | |
| Teton Sioux (the Lakota) demand one of the boats as a toll for moving farther upriver. A fight nearly ensues, but is defused by the diplomacy of a chief named Black Buffalo. | | |
| The Corps of Discovery reaches the earth-lodge villages of the Mandans and Hidatsas. The captains decide to build Fort Mandan across the river from the main village. | | |
| The captains hire Toussaint Charbonneau and his young Shoshone wife, Sacagawea, as interpreters. | | |
| The Mandans perform their sacred “buffalo calling” ceremony and a few days later, a herd shows up. | | |
| Sacagawea gives birth to a baby boy, Jean Baptiste. | | |
| Lewis and Clark dispatch the big keelboat, roughly a dozen men back downriver and boxes of scientific specimens for Jefferson. The permanent party heads west. | | |
| The Corps of Discovery enters what are now called the White Cliffs of the Missouri – remarkable sandstone formations that the men compare to the ruins of an ancient city. | | |
| The expedition comes to a stop at a fork in the river : which is the Missouri and which the Marias ? | | |
| Lewis comes across the Great Falls of the Missouri. They will have to portage eighteen and a half miles to get around them all. | | |
| The expedition reaches the Three Forks of the Missouri, which the captains name the Gallatin (after the Secretary of the Treasury, Albert Gallatin), the Madison (after Secretary of State James Madison), and the Jefferson. | | |
| Sacagawea recognizes Beaverhead Rock and says they are nearing the river’s headwaters and home of the Shoshones. | | |
| Lewis comes across a single, mounted Indian and tries to signal his friendly intentions, but the Indian rides off. | | |
| The shipment sent from Fort Mandan finally arrives in the East.That same day, Lewis ascends the final ridge toward the Continental Divide . | | |
| Lewis tries to negotiate for horses. Clark and the rest of the expedition arrive and Sacagawea is brought in to help translate. The Shoshone chief, Cameahwait, turns out to be her brother. | | |
| The expedition sets off over the Bitterroots. | | |
| They camp at a spot the captains call Travelers Rest, preparing for the mountain crossing. | | |
| The Corps of Discovery ascends into the Bitterroot Mountains. | | |
| After debating what to do about the strangers who have suddenly arrived in their homeland, the Nez Percé (on the advice of an old woman named Watkuweis) decide to befriend them. | | |
| Having raced down the Clearwater, then the Snake rivers, they reach the Columbia. | | |
| Clark sees Mount Hood in the distance, proof they are at last approaching the ocean. | | |
| Thinking he sees the end of land in the distance, Clark writes his most famous journal entry: “Ocian in view! O! the joy.” But they’re actually only at the eastern end of Gray’s Bay, still 20 miles from sea. | | |
| To make the crucial decision of where to spend the winter, the captains decide to put the matter to a vote. The majority decides to cross to the south side of the Columbia, near modern-day Astoria, Oregon, to build winter quarters. | | |
| In the East, President Jefferson welcomes a delegation of Missouri, Oto, Arikara, and Yankton Sioux chiefs who had met Lewis and Clark more than a year earlier. | | |
| Fort Clatsop is presented to the Clatsops, and the expedition sets off for home. | | |
| The expedition arrives back with the Nez Percé but have to wait for the snows to melt on the Bitterroots before trying to cross them. | | |
| After re-crossing the Bitterroots, the expedition splits into smaller units, in order to explore more of the Louisiana Territory. | | |
| Blackfeet warriors try to steal horses and guns at night. In the fight that follows, two Blackfeet are killed. | | |
| Downstream from the mouth of the Yellowstone, the entire expedition is finally reunited. | | |
| They arrive back at the Mandan villages.The captains say good-bye to Charbonneau, Sacagawea, and Baptiste. | | |
| The men see a cow on the shore and raise a cheer at the sign that they are finally returning to the settlements; that day they reach La Charette. | | |
| Their last day as the Corps of Discovery. They reach St. Louis. | | |
| The captains are national heroes; as they travel to Washington, D.C., balls and galas are held in the towns they pass through. | | |