When I was stationed there in the 1982-1984 period, most of the coastline was totally undeveloped. We used some of it to practice amphibious landings.
There was a nice beach in the southern part of it (Del Mar), just adjacent to Oceanside that was only accessible to Marines and their families.
I was stationed at Las Pulgas onboard Pendleton in 1968, just before I was sent overseas to Khe Sanh.
My parents lived in Palmdale, Ca, I was able to make the drive from Palmdale to Las Pulgas in about an hour and 15 minutes.
Now it takes about 4 hours to drive from Downey, Ca. to the north boarder of Camp Pendleton!