Wolf Den Run State Park is Maryland's first and currently only park that caters to four-wheeling. There are three designated areas, each with numerous trails. A permit is required. The trails are open year-round except for deer firearms season, the two weeks beginning the first Saturday after Thanksgiving. There is no camping at any of the three offroad locations, but a campground is 1 mile northwest of Huckleberry Roaks Area along N Hill Road.
Trail 2101 serves as the entrance trail for the Potomac River Area. There is a large parking lot a few hundred yards from the official entrance to meet and air down. The trail is a moderate climb for a little more than a mile. You'll see plenty of debris from the old coal mines on either side and smell the sulfur as you go through the murky puddles. There are rock obstacles, but none are very big, so you shouldn't require more than 4 Hi.