Q) Did the mountain men travel back and forth to the settlements on the supply route or an alternate route?
A) By 1830, through exploration and information from Native people, the American businessmen and field leaders in the fur trade had a solid and fairly accurate picture of the geography from the Mississippi to the Pacific. Land routes to Santa Fe, the Upper Green River Basin, California and the coast of Oregon Country were well established and generally known among the mountaineers. The Missouri River provided a major water route west which, by 1832, had proven viable for steamboats as far as the confluence with the Yellowstone. These were features in the mountain man’s mental map he used to navigate from place to place. This is not to say that mountain men didn’t trail blaze new routes after 1830, just that there were preferred and accepted routes between the settlements and major locations in the west by that time.
Supply routes to and from rendezvous and trading posts generally followed the safest, easiest path that provided grass and water for stock, or navigable water for boats. A mountain man traveling to and from the settlements would have had the same needs and would have made the same calculations that guided company boats and caravans as to what was the best way to go. His challenge would be to get from wherever he was to a spot where he could connect with one of the major routes, and maybe there find a group headed his way to enjoy safety in numbers.
This was the test of his mental map: to have an accurate picture of what drainage he was on, where that drainage lead, and what landmarks on the horizon could tell him about where he was in relation to the drainage he wanted to be on. His own experience, or information collected around the camp fire, would help him make use of trade routes, existing Native trails, and courses through easier terrain until he could join one of the well-traveled routes that led to his destination.