Here's a link to the map. Does Adventure Cycling even do mountain bike tours? In any event, I would ask them if it's all paved. However, I can tell you that I did a similar loop with a friend about 10 years ago starting and ending in St. George. It was entirely on paved roads. We went clockwise and passed thru Snow Canyon, Cedar City, Cedar Breaks (a significant climb), Panguitch, Bryce Canyon, and Zion. We did it in the 2nd half of May, and had very hot temperatures in St. George, and very cold temps (including snow flurries) at the top of Cedar Breaks. It was a very pretty route.