I did a tour around St. George and Zion last year - end of March, early April. It snowed in Zion and was down around freezing every night. Brrrrr! I think Cedar City and Bryce are even colder.

I think the ACA loop people are talking about is the Cliffs Loop. I downloaded the map and would like to try it someday. It's a lot of off-roading. I think a mountain bike would be better than a Randonee.