Hey Drew,
Private parks are where it is at in MI besides Silver Lake, The Mounds and Drummond Island. Below are
MY own PERSONAL opinions of the various places to wheel in the Great Lakes State.
Great resource:
http://www.offroadnorthamerica.com/parks.asp
-Bundy Hill Off-Road Park, Jerome, MI (never been there, old gravel pit and some woooded trails)
-Drummond Island ORV, Drummond Island, MI (Best fo the Best! But you already know that)
-Mounds Off-Road Vehicle Area, Mt. Morris, MI (Tons-O-Mud, some man made rock challenges and a lot of toophless, shirtless purple necks)
-Ottawa National Forest, Ironwood, MI (Pretty much in Sconsin' so I haven't been there yet. Heard good things about it)
-Rocks and Valleys Offroad Park, Harrison, MI (My #2 Favorite place to wheel in MI. Everything from mild to EXTREEME, great trails, tight trails, off camber, hill climbs, etc)
-Ron's Trails, Stevensville, MI (Only 15 acres "By invitation only" BOOOOOOO!)
- Silver Lake State Park (Silver Lake Sand Dunes), Hart, MI (I'll let others comment on this one. Let's just say I'm not a fan)
-Turtle Ridge Off-Road Park, Drummond Island, MI (Extreeme wheeling Private park on Drummond Island, haven't seen an H3 leave without some kind of damage, H2s and H1s too!).
-Twisted Trails Off Road Park, Copemish, MI (I hear it's pretty decent, but you have to drive past Rocks & Valleys to get there so why go an extra 2 hours north??? We will try it eventually)