Use caution and check for private property signs. This is a great trail, don't want to see it closed. I just road From the main trail up to the base of the jet eye and back to hulda crooks park via the razor back. The Trail past 4 courners isn't single track anymore. It's back to being fire road again until about 100 yards from the mouth of the jet eye.
Razor back is also very hard packed and extreamly ridable.
A few weeks ago there was a fire in the canyon and the fire trucks had to make a temporary road to get to the back of the canyon. Very difficult to ride into the canyon, but still pretty quick coming out. Loma Linda is a very kewl place to ride, there is tons of trails you can get to from the main trail head. The riding out there is a little bit technical, as long as you know how your ride responds you should be able to ride it with little to no problems. The sand is not a big problem, and the loose dirt is only on the main, wide trail where the motorcycles ride.