January 18, 1803, President Jefferson sends a secret letter to Congress asking for $2500 to finance an expedition to explore the Missouri River. The funding is approved February 28.

June 19, 1803, Lewis writes to William Clark, asking him to co-lead the expedition up the Missouri. Clark accepts in a letter dated July 19.

June 20, 1803, Jefferson addresses his instructions to Lewis.

July 4, 1803, Louisiana Purchase is announced

May 14, 1804, the Corps leaves St. Louis, Missouri

October 26, 1804, the explorers winter with the Mandan Indians

November 4, 1804, Sacagawea joins the Corps

April 7, 1805, the party sets off up the Missouri River again

June 13, 1805, Lewis and Clark reach the Great Falls and begin their month-long portage

September 11-22, 1805, the Corps crosses the Continental Divide

October 7, 1805, the expedition starts down the Clearwater River, to the Salmon and then the Columbia

November 8, 1805, Lewis and Clark reach the Pacific Ocean

March 23, 1806, the party leaves on its return trip, later splitting into two groups

July 3-August 12, Lewis explores Montana’s Marias River

July 15-August 12, Clark explores the Yellowstone River

August 12, 1806, the Corps of Discovery regroups to return to St. Louis

September 23, 1806, the Corps arrives in St. Louis