"Wagon Trains" traveled over known and established routes, these also not coming around until much later in the 1800's, these were also well planned affairs VS "set of your pants - follow the buffalo into the wild blue yonder" free roaming unprepared adventures, such as the first adventure. Also, the typical "safe travel" season, depending on route and altitude and exact region, would have been from say, June through to September, with September even becoming questionable due to common early snows. Just saying.....
PS: I have friends that live in this very region, a landscape photographer who is always out and about, "until September" and often not until late June in some areas depending on the spring snow melt. Now then, he drives a lifted jeep and he has established roads and trails to travel, some of these even bringing his jeep to a crawl for considerable distances as he negotiates the rock, ditches, ravines, etc., etc., etc. Just saying.........so unless this fantastical mine was at low altitudes and easily accessible right off of an established trail......