I can't offer precise feedback like Hogwild has (few are there who can), but I did this trip report about that area last March (here
We approached it from the west, camping 45 minutes south of Mesquite. The video of the first day is further to the west than you're planning, but the other two videos in that trip report are in the western edge of what you're thinking of riding.
You'll see some pictures of us in tall pine trees. That the area overlooking the Virgin River Gorge. Had we gone another 10 miles or so I think we would have reached a lookout point, but we were worn out fighting the mud and turned back before that point. I'm guessing that area will be as easy to reach from St. George as it was from Whitney Pockets.
The third video is just riding around on a lot of the flat dirt roads crisscrossing the northeast corner of AZ in Grand Canyon/Parashant NF. It was a fantastic area to ride.