CO also requires an OHV permit for a street legal motorcycle if you ride it on a trail. The very act of riding your street legal motorcycle off the pavement makes it an OHV. I'm OK with that as long as they spend it on the trails and don't put into the general fund.
I haven't ridden around Durango, but I have ridden a good bit around Ouray, Silverton and Telluride. Also rode a good bit around Taylor Park, Creede, South Fork, Gunnison and Lake City. Your best bet is to get some of the Motor Vehicle Use Maps from the Forest Service.
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd492994.pdf
