I'm guessing, but I've heard of this before. The Forest Service grants the special use permit on the condition that no maps are handed out, and no GPS's are used, so that the trails won't get more use after the event. After the ride, all the trail markers have to be removed so that the roll charts are semi-worthless, too. They're protecting public lands from the public.

I've been told by a FS law enforcement officer that it was against the law to possess a trail map of an open riding area on National Forest land. What sense does that make? I guess they'd rather you wander into a closed area, then they can ticket your axx.