There are several things to consider here some horses dont handle the mountains well psycholgicly seems to freak them out so make sure you bring well broke horses that can stand being tied sometimes for long periods.
Make sure they are good and fit and well shod.I would get them in some hill country to get them fit to prepare them for climbing.Packers pellets are probably a good idea for feed to carry on your way in and out.Personally I would also want a pack animal that has experience packing dead game,it can be a hell of a wreck trying to put a bear on an animal the first time.w/regards