In the early 1800s, Colorado was an unknown expanse of wilderness. Adventuresome beaver trappers and explorers explored its valleys and forests, established forts, encountered Native Americans and drew the first rough maps. It was not gold that originally brought the first visitors from the East coast to the Rocky Mountains in the early 1800s; it was fur.
The high fashion of the day–beaver fur hats–created a demand for beaver pelts. In the 1830s, more than 500 trappers roamed the Rockies trapping beaver and selling pelts for $5.99 a pound in Philadelphia. Trading posts were located on the Arkansas and South Platte Rivers to facilitate the trade in beaver pelts and a burgeoning trade with the Native Americans for buffalo robes.
Rugged mountain men trapped in the Tarryall region along the South Platte river in the winter, leaving the valley to the Utes in the summer. By the 1840s, the top hat fad had ended, and the demand for beaver dwindled. Most mountain men moved on to look for other occupations–mining or trading for buffalo robes.