George Rogers Clark was born near Monticello.
Just before the purchase of Louisiana, President Jefferson had recommended to Congress (18th January 1803) the sending of an expedition to explore the headwaters of the Missouri, cross the Rockies and follow the streams to the Pacific. In accordance with the recommendation Meriwether Lewis and William Clark, both officers of the United States Army, with a considerable party left St Louis on the 14th of May 1804, ascended the Missouri to the headwaters, crossed the Rockies and, following the Columbia river, reached the ocean in November 1805.
The main range of the Rockies follows the boundary line between Montana and Idaho west and north-west from Yellowstone Park in Wyoming to Ravalli county, then turns eastnorth-east to Lewis and Clark county, and from there extends' north-north-west into Canada.
In the north the Rocky Mountains consist principally of two parallel ranges, the Lewis and Clark Range to the east, and the Livingston Range to the west, which were formed by a great overthrust; between them is the Waterton-McDonald valley, 8-15 m.
The east slope of the Lewis and Clark range is marked by long high spurs, and the valleys between them end in radiating canons that are crowned with bold cliffs.
