This is a good place to let any locals no where you go off roading. Mention in your post:
The location
What it is... a park, rocks, trials, mud
What kinda rigs normally are there..

 

Pinckney michigan...... some serious offrading at some of my buddies houses out in the sticks.....we are talking 20 - 30 ft mud holes and a lot of rocks to climb....industrial farm tractors to pull you out plus mopst these guys got 72 inch tranctor tires or straight monster trucks.....20 dollar entrance fees and waivers to be signed

 

The only ones that come to mind in michigan are:

Silver Lake State Park, Hart, Michigan
http://www.silverlakesanddunes.com/drivingonthesilverlakesanddunes.html

Mounds Off-Road Vehicle Area, Genesse county MI
http://www.geneseecountyparks.org/mounds.htm
6145 E. Mt. Morris Rd. - 1.5 miles east of Genesee Rd., Mt. Morris, MI 48458
Monday – Saturday: 8:00 a.m. – Sunset
Sunday: Noon to Sunset