Who were mountain men

A. men who led wagon trains on the Oregon trail

B. mormon missionaries seeking to convert indians in the rockies

C. expansionists who favored increased westward migration

D. young american trappers and traders in the rocky mountains

D.

Mountain men were most common in the North American Rocky Mountains from about 1810 through to the 1880s

The correct answer is option C. Expansionists who favoured increased westward migration.

Explanation:

These mountain explorers, who moslty lived near the Rocky Mountains, greatly contributed to the migration of colonists into the far West. They explored areas, opened up trails for the migrant colonists to pass and improved the roads for the wagon trains (a group of wagons) to head into the West. These trails and roads were also used to transport fur during the emerging and profitable fur trade.