The name brand mountain bike trail system of Gunnison is definitely Hartman Rocks. When we rolled into town, it was lightly raining. According to the Quality Inn front-desk staffer, it had been for 1.5 days. To prevent damaging choice single track, we took to the double track right behind our hotel.
There are all kinds of single and double track trails crossing through the sage brush in the hills behind Western State Colorado University. The Ridgeline trail to Signal Peak is rocky/sandy double track most of the way, until we had to turn around 300 ft below the summit of Signal Peak.
RT ~10 miles. ~1500 ft elevation change. 2 hours out and back to where we got stuck in the mud.