Dave, I drove from pine to foxton the other day. The river goes through a very mellow scenic valley from pine to buffalo creek. Its mostly meandering class I/II. There were a few rocky ledges (manmade) that should be easy to portage if needed. You could probably find a spot to put in at pine, or maybe float down from pine valley ranch. Its definitely mellow below pine, not sure what's between pine valley ranch and pine though. Private property could be an issue. For most of the run through the valley the river is visible from the road, but there are farmers fields between the road and river. The river comes back close to the road before it goes into some class III just before buffalo creek. Its mostly visible from the road so you could likely road scout the entire thing and figure out best put in and takeout from the road.
Google earth shows the valley nicely for a couch scout. After buffalo creek, the river gets into II/III for a ways before the traditional foxton put in, but its likely more than you are looking for with Riley.