The Mounds is a fun place to go. Straight up I-75 just North of Flint. Get off at Mt Morris, go right about 10 miles and it will be on your left. A few hundred acres if I remember right. Otherwise you will have to go about another 1 1/2 hours north to St Helen. There are a few places around there.
I think they have a website, probably Themounds.com
Wish my Bronco was ready, but I could bring the four wheeler. Let me know what you guys come up with.
You will need an ORV, there is a place on the way about 1 mile from there that sells them, a party store on the left. It is on a corner lot on two somewhat major roads.