If you get over by Danburry Wisconsin they've got some great trails.

 

Red top is a good trail. The closest one to the Twin Cities is in Fairbault. It's just a small gravel pit but it is still state funded and is on the map. I have also been to Fort Ripley and Spider Lake.

 

Sounds like you found Red Top! It's one of my favs.

These guys have a good writeup on it for anyone else finding this thread: They call it one of the best public ATV trails in mn

You should also check out St. Croix it's not as technical, but if you're in the area it offers some really fun ATV trail riding.