A more challenging trail running opportunity, the Sunnyside Trail stretches 10 miles between the Hunter Creek Valley and Red Mountain. It’s a moderate dirt singletrack through groves of aspen, marked with stunning views of the mountain and surrounding valley. From town, most runners access the trail from Cemetery Lane or behind the Hunter Creek condominiums. The trail climbs steadily up Red Mountain, which is the rough halfway point. For a shorter run, start on the Cemetery Lane side and continue to the second intersection with the Shadyside Trail before turning back for a roughly 6-mile round trip. Especially pretty in autumn!
This Forest Service trail description is a good resource.