 In 1802, after the Spanish territory of Louisiana was given back to France through treaty in 1800, trappers began entering the Louisiana Territory and trapped beavers in the mountains.In 1803, the United States purchased the land which encompassed the present state of Colorado with the Louisiana Purchase and explorers came to the area to survey the land.The trail was an important trade route for fur trappers and traders in the North American fur trade from about 1820 and into the Pikes Peak Gold Rush beginning 1859.