Compared to almost any other country, the United States has few truly regional foods. But there are notable exceptions of cities or regions that serve dishes that are uniquely theirs. The art of barbecue perhaps best exemplifies this. If it's barbecued brisket you crave, you go to Texas; if it's pork shoulder, Memphis is your best bet.
I would extend this phenomena to what is somewhat inaccurately referred to as "ethnic food." Due to seemingly random immigration patterns, certain diverse communities have introduced their specialty foods to the fortunate inhabitants of particular cities, so much so that one community's unique dish or cuisine can be best enjoyed only in that city. For example, when I left Washington, D.C., a dozen years ago to come to San Francisco, I knew my taste buds would henceforth be deprived of the greatest examples of the spicy Ethiopian, and particularly Eritrean, food found outside of eastern Africa. Other cities blessed by these strong culinary ties include San Francisco (Cantonese), Miami (Cuban), Chicago (Polish), and New York City (Jewish, Korean, Caribbean and Indian--lucky New York).
I add San Diego to that list, although I would whittle its associated food down from a region to just one dish: the Baja fish taco.
Whenever I have returned home from visiting my brother in that city, I regretted that I couldn't find authentic fish tacos back in San Francisco. You could argue that my fish taco envy ended when San Diego's own Rubios's opened a branch here a couple of years ago or perhaps when Taylor's Refresher started selling its quite delicious rendition at the Ferry Building.
However, it was my first bite of Cocina Primavera's fish tacos, only occasionally sold at their stand at the Saturday farmers market, that truly turned the fish taco equation forever upside down. The Primavera taco starts out at an advantage with one of their own soft, hand-made organic corn tortillas. The cook then tops it with expertly fried pieces of catfish encased in a gossamer beer batter, spicy chile de arbol salsa, creamy avocado mayonnaise, cold shredded cabbage and a piece of radish, served with a wedge of lime on the side. The flavors and textures create a fiesta in your mouth of contrasting flavors and textures. Although it's not really a restaurant, I definitely add this humble food stand from Sonoma to my Short List.