Stay along the trail. Bikes are not allowed in the wilderness that borders the road on both sides.
This Jeep road is burly and loose enough to require singletrack skills. You'll find a few intricate sections and it needs some careful line choices if you're wanting to keep rolling along. Having mentioned that, this is not a risky trail and any difficult sections are short and easy to portage. It's very easy to find the route.
There is one major fork along this stretch. If you are heading east (up canyon), the left fork is the easiest choice and this is the recommended option (more advanced riders may want to try the other side on the way downhill, but it's pretty loose and has a lot of chunky debris).
As you reach the end of the GPS track, you'll spot Skull Rock just past a short rise (the trail forks here and continues, but this also serves as a nice lunch spot / turnaround point.)