If you don't need whitewater and you want solitude, go out past Grand Junction and do an overnighter and run the Colorado from Loma to Whitewater through Horsethief and Ruby Canyons, but not now. Wait until well after Labor Day and go mid-week. You will go through some amazing scenery. For a day trip, do the Upper Colorado from Pumphouse to State Bridge, and you get a little whitewater (II) and a hot springs pool. Right now both stretches are circuses, but I've done both in the Fall when nobody else was ever seen.