There really isn't anything legal near Petoskey as for state land. As mentioned, Twisted Trails is a private park and is a little over an hour away. On the other hand, I'd go the opposite way and hit Drummond Island. It's a bit further, and requires a ferry ride, but there are about two solid days worth of wheeling to be had there. Its a nice area and a great place to spend a weekend. It's also the premier location for state land wheeling in Michigan. For more challenge, there is also Turtle Ridge offroad park on the island as well.
The other option would be to go further south and hit some of the trails around Grayling, which are ok, or further yet down towards West Branch / St. Helen. The Grayling trails are mostly forest roads and many are used for military training. The ones around West Branch / St. Helen offer tighter trails.
No matter where you go, Michigan only offers at most about 1900 ft of elevation change and only about 1500 ft variance in the lower half. The DNR isn't exactly pro-wheeler either so public land doesn't exactly offer a challenge so if you are looking for that head straight to the parks. If you are looking for some nice scenery and some fun exploring, then you'll have lots of fun on the state land.
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