Lewis and Clark hire Toussaint Charbonneau as a guide and he and his wife Sacajawea join the party Read more: http://wiki.answers.com/Q/What_are_some_important_dates_of_the_Lewis_and_Clark_expedition
Sacajawea gives birth to her son, Jean Baptist
The expedition lands at the mouth of the Columbia River, Astoria,Oregon
The expedition group begins its way home
The expedition splits into two teams
So Lewis could go explore the Marias river.
The expedition team reunites at the Yellowstone and Missouri Rivers