are you primarily looking to GMU35 for access from the river? because there's a road on the GMU25 side that runs along the river most of the way, which gives you access anywhere along that road as its mostly BLM
also if you zoom in, you'll see that Colorado river is in a fairly steep canyon most of the way, so even if you got off on GMU35 side, it would be a straight hike up a very very steep wall. then you also have the boat to worry about *(assuming you have a raft?).
i float Colorado between 15/361 areas, and in the summer/fall when water is low, one can find plenty of spots to wade across. *(as long as water flow is low), but am not so sure further down where you're thinking if its possible to cross on foot.