Pawnee Grasslands Scenic Drive: Ault to Sterling is a 125 mile trail located near New Raymer, CO. The trail is primarily used for scenic driving and is accessible year-round.
From the time you leave US 85 on County Road 90 (or if leaving from Ault you may take 14 to CR 90) you will know that you are in some big empty country. The overview says that it is open year round but don't even think about it in a blizard. The snow can drift quick and deep in places.