I agree with joe and the master, It's far more the individual horse than the breed. We use Quarter, Thorough, Arabian, Paint, as well as mixed breed and they do well because they live in the mountains, they get ridden in the mountains and we know the horses and the temperments of each horse. One thing to keep in mind is if you are a rookie at riding horsed don't let the horse know it. Make the horse know that you are in control, If you let it do what it wants then you will have a hard time getting it to do what you want when you want it to do it. Draft horses, although very strong, are pretty big horses to be using in the back country of the Rockies. There can be alot of tight places in the wilderness. Tenessee Walkers make good "trail" horses, they are strong and have a medium frame and tend to be very sure footed in general. Again it can depend alot on the horse itself. Just remember you are NEVER actually in control, the horse only thinks you are. Don't let it know any different.