Montana By eme109331 1773 Francois and Louis de la Verendry explore the northern Great Plains. 1803 Eastern Montana, as part of the Louisiana Purchase, becomes U.S Territory. 1805 Lewis and Clark travel through Montana on their expedition through the Northeast. 1807 Manuel Lisa builds first fur-trading post; John Colter crosses the area of present-day Yellowstone National Park. 1857 Gold is discovered at Gold Creek 1872 Congress establishes Yellowstone National Park, the county's fist national park 1876 Sioux and Cheyenne Indians defeat George Custer in the Battle of Little Bighorn 1889 Montana becomes the 41st state 1894 Voters select Helena as the capital 1910 Congress establishes Glacier National Park