In Southern California, Mexican restaurants are pretty much on every corner.... the ones that aren't excellent usually close quickly.
In my experience, any Mexican restaurant that is a chain is probably bad (too Americanized, too expensive, too culturally silly). The best tend to be small "Mom" and "Pop" ones that specialized in a region in Mexico. I especially like the ones where the staff struggles with English and my wife orders for us (she speaks Spanish, I don't)... and Spanish is the language you hear from customers. And don't overlook the fast-food and roach coaches ... sometimes they have the best Mexican food, better often than the sit down restaurants.... LA especially is famous for these.
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