Thing Valley Road is an easy to moderate road that goes from Sunrise Highway near the entrance to Bunt Rancheria Campground to La Posta Truck Trail in Thing Valley, about five miles. The entire road is open when weather and fire conditions permit but there is a gate that is locked year round about three miles south of Sunrise Highway. This is to prevent through traffic from bypassing the Border Patrol check point on I8.
The road north of the gate is easily passable with a 2WD high clearance vehicle. South of the gate the road is steep and has some difficult spots. A 4WD high clearance vehicle is required, especially if you are going uphill (south to north). To reach the south part of the road you will either need to take Fred Canyon Road or La Posta Truck Trail.
Difficulty: north of the gate, easy (2); south of the gate, moderate (3), possibly difficult (4) if going uphill (south to north).
I drove this road on 10/13/12 with my Subaru Forester. I came up Fred Canyon Road and drove Thing Valley Road downhill. There was a hairy spot near the top where I had to get out and survey ahead. It wasn't as bad as it looked from inside the vehicle and wasn't difficult to traverse at all. However, I was going downhill. I read another report that said you will need low range to take this road uphill. At the bottom I exited via La Posta Truck Trail, which is a freeway by comparison. Overall, I think you could take the complete loop (Fred Canyon Road, Thing Valley Road, La Posta Truck Trail) in a 2WD high-clearance vehicle if you start at the Fred Canyon Road end. However, if you go in the opposite direction you will probably need a 4WD vehicle with low range.