[rbrADV]

Definitely need to get a day pass for the White Rim Trail now. It is a formality to get a count of the number of vehicles per day.
I also rode the Onion Creek Road as part of the UTBDR last year - excellent!

The LaSal Mt Loop is on the way to Onion Creek - should be great color that time of year.
May also be able to include a stop at 3 Step Hideaway - a camp that caters to ADV bikers.
If you haven't ridden to Chicken Corners that is worth the trip. Long stretches right along the Colorado River.
Of course, a quick ride through Arches Nat'l Park is a possibility. (It is free if you make a loop and ride in from the north side - although several miles of sand.)