And for all those who don't think that a massive firestorm is a plausible backdrop for a Calfree->PCC->Aztalan war, consider this: in the last three weeks,
nearly half a million acres of grassland in the LA and San Diego areas have burned. I doubt that even made nationwide news, though, because it happens damn near
every year and we're used to it.
See, most of Southern California, particularly the areas around LA and San Diego is arrid grassland. SoCal has basically two seasons: the Rest of the Year and a 1-2 month Fire Season where nature has dictated that the whole countryside is supposed to burn down and grow back from the ashes. The main reason LA doesn't lose thousands of homes to the flames every year is because the people around here got smart a ways back and are relatively good about clearing the brush out of their yards, which gives the fire crews room to work.
But say, for instance, that another nation, unfamiliar with SoCal's oddities, moved in and took over. Let's call them Pueblo, hypothetically. Let's also suppose that due to the general cooling trend we've been experiencing for the past 150 years SoCal has a series of unexpectedly mild Fire Seasons, such that Pueblo decides, over native objections, to cut the firefighter's budgets to 1/4 or less what it was. Say people have been "encouraged" to relocate from their houses, and trash, debris, and brush crowd the streets and the areas that used to be firebreaks. Now imagine 50 MPH Santa Ana winds, dropping the humidity near zero for three weeks. Also imagine a few "deniable assets" hired to be fire crews in reverse.
BAM! In less than two days six million acres go up in smoke. Half the city's underfunded, underpaid, aging firemen "go on strike," being encouraged through various channels to do so. The ash and soot linger in the LA basin, forcing pollution to such levels that the sun is half-blocked (happenned during the Malibu fires a few years back; damn but that was freaky.) After a suitable period Calfree "relief workers" saunter down the I-5 and Highway 101 and sweep all the way down to the old Mexico border. Pueblo can't do much about it because Palm Desert and Death Valley prevent anyone from traveling through that route, and the only other way (the mountains) is a choke point waiting to happen.
We'd call this series of adventures "Firestorm", put it in an adventure book or sourcebook of some kind, and involve runner plot hooks evey step of the way. Doesn't that sound neat?
All these ideas are free. Unfortunately Canon's decision was that LA has become an island. LA is a basin, surrounded by hills; it has about as much chance of becoming an island because of an earthquake as New Orleans does of becoming a mountain because of another hurricane.