Meriwether Lewis and William Clark leave Camp Wood. Before the expedition, Lewis prepared by educating himself in many categories of science like biology and astronomy.
As they moved into the Great Plains, they start to discover plants and animals they've never seen in the east: coyote, mule deer, ect. In all, 178 plants and 122 new animals were found that have never been discovered.
Clark notes a temperature 45 degrees below zero. They recorded it as the coldest they ever knew the States could be.
The Mandan's do their sacred "buffalo calling" to attract buffalo that would come in later days. The Mandans and explorers get along together very well and without them many of the explorers could have died from frostbite.
Sacagawea gives birth to a baby boy, Jean Baptiste. This was an addition to the other 4 dozen people on the expedition.
Proceeding to what is now Montana, a place that white men have never reached, the explorers run into herds of buffalo. The men at an estimated 9 lbs. of buffalo meat a day.