The Natural History of the Long Expedition to the Rocky Mountains (1819-1820) (repost)

A little over 170 years ago--hardly a moment on the clock of history--one half of the United States was empty of all but Indians and the plants and game on which they subsisted. Indeed, acquiring the Louisiana Territory approximately doubled the size of the United States, adding 800,000 square miles of land that had scarcely been explored or adequately mapped.