Lewis and Clark expedition

 On May 14 in 1804, the first overland expedition across the North American continent set out from St. Louis, under the leadership of Captain Meriwether Lewis and Lieutenant William Clark. The expedition had been ordered by President Thomas Jefferson in order to get a sense of the land recently acquired from France through the Louisiana Purchase. The expedition would take Louis and Clark, and about 40 others, up the Missouri River, through the Dakotas and Montana, across the Continental Divide, and eventually down to the mouth of the Columbia River. At the request of President Jefferson, Lewis and Clark kept detailed journals, in which they kept a record of their adventures, and of the plants and animals they encountered on their way. They listed 178 plants and 122 animals — many, like the lynx and the prairie dog, now at risk of extinction.