I really would encourage you to visit Arches NP:
http://www.nps.gov/arch/
right outside Moab. Over 2,000 natural arches in the park. Moab is on the Colorado river and has river rafting etc. Moab is also a center for mountain biking and has the Moab jeep safari where jeepers test their equipment.
On the way to Moab is Green River, UT, the site of the best watermelons in the world (IMHO). Festival every Aug.
GW mentioned the Shakespeare theater in Cedar City and that is great with performances daily. (Its not THAT out of the way-GW)
River rafting? What a great idea. I know we would love it.
Thanks.