From the little I know about Sedona, I would think it`s going to be pretty chily in December. My one trip there (so far) was in late Oct or early Nov, it seems to me, and it was very nice weather at that time. There`s a great sticky on the "Arizona" section over at mtbr- that`s the place to ask about mountain bike rides if you don`t find out what you need from here. Have a great trip! It`s a wonderful place for riding and hiking.