Just think about it. They already have the NG from SD up to Orange County, LA and Riverside. Those are the 4 main counties in Southern Calif. Now add in the Coachella Valley and you pretty much have Southern California locked down. The only thing beyond that is Arizona.
Okay, I'll think about it: -Coachella Valley is in the aforementioned Riverside County -You left out San Bernardino if you mean "main county" in terms of population or area -You also left out Imperial if you mean border counties
What is Imperial Valley's main industry? Figure that out, and there's your answer.
FYI, not everyone on BlueSky lives in California, or the Unisted States. Which means that many readers have no fucking clue what you are talking about.
Thanks for your eloquence.
Industry info is available online. Imperial is known for agriculture. (The Central Valley isn't the only spot.) As you mentioned, there is nothing really to the south as far as infrastructure. They would have to base operations in, say, Indio, IMO, or camp out with scorpions.