I hadn't heard that, just people that go to CA to vacation always say "if you go to CA you have to go to In-N-Out". We were over your way in February, but never did make it to one. Next time we will if they aren't here yet.
Add: In SoCal go to El Pollo Loco, Super Mex, Rubio's, and Whahoo's. El Pollo Loco started in Mexico, but is "American" now. The other three are SoCal based; the latter two based mainly on fish tacos.
As a SoCal native, Mexican "style" food is my favorite diet. Mix them up. Cal-Mex; Tex-Mex; Mex-Mex, Surf-Mex...just hurry up and serve!! How about Arizona-Mex?