heres a more specific map of the San Jacinto mountain where 4S21 is located:
At best 4S21 is intimidating to beginners while being technically easy. Its very scenic at least. It has the highest difficulty level on the signs I think (the black square with the very jagged line)
If you are into shooting and havent been here, it might be a good trip to see the shooting areas to know if its somewhere you might want to go or not. They are totally legal and we will pass within a few feet of them on the way up.
EDIT: Actually I cant seem to find a video of the "difficult" parts of 4S21..they all seem to show the very beginning which is really easy.