Could go either way; for a short time in 1967 I was attached to an artillery battery that was indeed way out in the boondocks there; most artillery exercises took place at 29 Palms, though - at that time it was stricty an artillery base.
When I was stationed in SanDiego, I used to go pick up an old friend of mine on Camp Pendleton. His barracks was about a 45 minute drive from the back gate. I always wondered about the sign I would pass that said “End Of Overhead Artillery Range.” I never saw a “Begin Overhead Artillery Range” sign.
Major road hazards on that part of Pendleton:
Fast moving M1 tanks crossing the roads and bison.
Might have been mortars. I heard that it was supposed to be sometime around early 1970 but that is anyone’s guess, even whether it is true or not. You’re right about 29 Stumps; most of the practice was there. I spent time at Barstow (supply center) and had some buddies stationed at 29 Palms.