Wharton and Colliers mills are legal to drive on the trails that are marked. In colliers mills that basically means any trail that the jeep can fit down, Wharton is slightly more complicated because there are some areas that are closed down to vehicles but can be hiked. The colliers mills reserve is most likely what you accessed from off of reed road, if you look on google maps and use the satellite feature you can see the trails and the trail names in each. I'v been wheelin colliers since I was a kid and seem to never get bored of it, here is a pic from christmas eve wheelin!
Managed to find the only large rock in the area!