This is a multi-use area that is a maze of trails made by motorcycles & ATVs.
Royal Blue is also known as Koppers Wildlife Management Area. It's nearly 50,000 acres multiuse wilderness area. The trails range in rideability but you'll definitely find something you like. Bring a compass or any map you can find. Odds are you will get lost at some point. From I-75, you can ride 10 miles to the Walnut Mountain Towers, or make a loop via Short Mountain. Otherwise just explore but give yourself plenty of daylight.
How to get there:
Take exit 141 from I-75, head East and park.
Ride in the dry season. Avoid during hunting season (Oct to Dec) or wear at least 500 sq inches of orange material