I say just go to the National Forest out there in the Sierras. Plenty of fire roads and other little trails to explore. Most of the roads can be done with any 4x4 mid size SUV so a XJ is perfect with a nice set of tires. From all the places Ive gone you shouldn't really have any issues, the biggest problem would be traction and steep hills. Just be careful and use judgment. If in doubt check it out on foot first and then drive up the trail more. You can't always rely on trail signs because a lot of times the trail is unmarked or the sign is missing. Typically if the trail is some what challenging for a stock SUV it will be marked with a little Jeep symbol or have a warning for "high clearance vehicles only". Just bring the proper gear and I always carry stuff in case I need to hike out or stay the night.