Great Sand Dunes High Dune is a premier hiking destination in Mosca, Colorado, covering 2.5 miles with 700ft of elevation gain. Stats: 2.5 miles, 700ft gain, Moderate. Type: Out-and-Back. Surface: Sand. Time: 2-3 hours. Fee: $25 GSDNP fee. Dogs: Yes. Permit: No. Wildlife: mule deer, elk, pronghorn, red foxes, raptors, sand tiger beetles. Best seasons: May through October for Medano Creek wading at the base; winter offers snow-dusted dune walking. Great Sand Dunes National Park contains the tallest sand dunes in North America — up to 750 feet tall. High Dune is the most prominent summit from the main parking area, a quad-burning slog up soft sand that rewards with a surreal Colorado views. Pack plenty of water — desert and high-altitude trails demand more hydration than you expect. Layers are essential above 10,000 feet. Leave No Trace: stay on designated trails, pack out all waste, and respect wildlife and other visitors.