Horsecreek , thats a good question , and I haven't been able to get a straight answer on that .
Even the lower Corner Canyon trails that are not in the wilderness area are confusing , and seem to change from time to time if horses are allowed . It's not my favorite place to ride , so I only go there if I need a quick ride .
Last week I was riding a trail from lower Corner canyon that has been open to horses according to my trail map from Draper City . I just happened to look at one of the new maps posted on a information booth by one of the restrooms , and that map advised the trail was closed to horses . My neighbors kid works for Draper City parks , and he doesn't even seem to know what trails are open for horses .
As far as the wilderness area which is pretty much every thing above the upper Corner Canyon road is open to horses as far as I know . Draper City has no control or any thing to do with the wilderness area , and from my research of wilderness areas I don't see how they could or can ban horses in a wilderness area unless there is some other factor like watershed protection area .