I took a bighorn in unit 21 last year. I would have to say that most of the elk are up on top, meaning, up about 3-4,000 vertical feet above the river. That isn't to say that you don't see some cows along the river early, but I would say most of the elk are up at altitude. The problem with staying by the river is how long it will take you to travel to the top. On most of the roads it takes atleast an hour of grinding up switchbacks to get to the top. If I were you I would camp up on top. I think the hunting should be pretty good up there, good looking country. Another bit of advise would be to do a scouting trip with the family, get some river time in, and go up on top to scout for elk, just my thoughts..