They were instrumental in opening up the various emigrant trails (widened into wagon roads) allowing Americans in the east to settle the new territories of the far west by organized wagon trains traveling over roads explored and in many cases, physically improved by the mountain men and the big fur companies, originally to serve the mule train-based inland fur trade.

Others, like William Sublette, opened fort-trading posts along the Oregon Trail to serve the remnant fur trade and the settlers heading west.

[2] The rendezvous system was later implemented by William Henry Ashley of the Rocky Mountain Fur Company, whose company representatives would haul supplies to specific mountain locations in the spring, engage in trading with trappers, and bring pelts back to communities on the Missouri and Mississippi rivers, like St. Louis, in the fall.

This system of rendezvous with trappers continued when other firms, particularly the American Fur Company owned by John Jacob Astor, entered the field.

The last rendezvous was held in 1840, when the HBC, along with a decline in demand for and supply of beaver, had effectively put all American fur traders out of business.

Soon after the strategic victory by the HBC, the Snake River route was used by emigrants as the Oregon Trail, which brought a new form of competition.

After the decline in beaver and the fur trade, with some emigrants to the West using the Mormon Trail, former trappers found work as guides and hunters for the traveling parties.

Both companies undertook numerous measures to prevent American fur traders from competing with them west of the Rocky Mountains, especially in the upper Snake River country.

After the HBC took over operations in the Pacific Northwest in 1821, American fur traders in the Snake River country quickly went out business and moved on.

[4] Mountain men were instrumental in opening up the various emigrant trails (widened into wagon roads) allowing Americans in the east to settle the new territories of the far west by organized wagon trains traveling over roads explored and in many cases, physically improved by the mountain men and the big fur companies originally to serve the mule train based inland fur trade.

They faced many hazards, especially when exploring unmapped areas: biting insects and other wildlife, bad weather, diseases of all kinds, injuries, and the opposition of Indigenous people who presented constant physical dangers.

In order to stay alive, the men needed keen senses and knowledge of herbal remedies and first aid, among other skills.

The mountain men dressed in suits made of deer skin that had stiffened after being left outdoors for a time, which gave them some protection against the weapons of particular enemies.

[8] There were no doctors in the regions where mountain men worked, and they had to set their own broken bones, tend their wounds, and nurse themselves back to health.