North of the Border, It's Everyone's Mexican Food ADMIT it, tortilla-chip fans: you are curious about Taco Bell Doritos Locos tacos, introduced in March. These salt bombs take the usual fast-food taco filling and stuff them inside a giant orange-dusted nacho-cheese chip. They have been so successful that the company has just introduced a Cool Ranch flavor. But to truly grasp the significance of these creations, the taco must be eaten in the company of Gustavo Arellano, a journalist and Orange County, Calif., native who is perhaps the greatest (and only) living scholar of Mexican-American fast food. And preferably, you will eat it here, in the birthplace of American fast food, while he explains to you precisely how the Frito, America's first corn chip, was copied from the Mexican tostado, then evolved into the Dorito and eventually the Tostito. He has just published "Taco USA," an absorbing account of how a few foods (salsa, tacos, chili, tequila) from the complicated and enormous cuisine of Mexico managed to slip into the mainstream of American taste. "It's not exactly a feel-good story, except maybe for the shareholders of Frito-Lay," he said, gesturing out to the empty storefronts and cash-only gas stations that line the streets. San Bernardino, an hour east of Los Angeles, is the fertile crescent for American fast food, but the west side has clearly seen better days. In 1940, the first McDonald's drive-up hamburger stand opened a few blocks from this Taco Bell; throughout the "40s and "50s, entrepreneurs came through town to check out the McDonald brothers" revolutionary technology hacks - like single-serving ketchup dispensers, burger-size spatulas and disposable milkshake cups. In 1954, Ray Kroc, a salesman of milkshake mixing machines, came through town and was so impressed that he bought in, started his own franchise, and later bought the brothers out. The evolution of Mexican food in the United States is the current obsession of Mr. Arellano, the editor of The OC Weekly, a lively journal where he has also been the food critic for the last 10 years. He has spent much of that time exploring precisely how Mexican food became so popular and profitable in this country - where, until very recently, most things Mexican were generally both unpopular and unprofitable. For the purposes of Mr. Arellano's tale, the story of the fast-food taco begins here, on the corner of North Sixth and Mount Vernon streets, where Route 66 used to run through town. Mitla Cafe, a modest restaurant serving typical Mexican-American food, has been on this corner since 1937 and is still owned by the descendants of its founders, Vicente and Lucia Montaño. It's the oldest Mexican restaurant in the Inland Empire, the vast tract of sage and scrub east of Los Angeles, now covered with housing developments and strip malls, and home to millions of Mexican-Americans. San Bernardino County's population is almost 50 percent Hispanic, according to 2010 Census figures. Mitla is not a destination for huitlacoche, epazote or a rigorously authentic mole negra. It is old-school Cal-Mex, with burgers and grilled cheese on the menu. Plenty of patrons eat fries with their enchiladas; Pepsi products, not aguas frescas, fill the drinks cooler. But Mitla does serve a signature Mexican-American dish: tacos dorados con carne molida, "golden" tortillas fried to order and folded around a spicy compressed wedge of ground beef, blanketed with iceberg lettuce, chopped tomatoes and shredded Cheddar. (The hard-shell taco is not unknown in Mexico, but it is usually deep-fried with the stuffing already sealed inside it. These proto-tacos can still be found at Cielito Lindo on Olvera Street in downtown Los Angeles, where the recipe hasn't changed since 1934.) At Mitla, the tortilla is hot and crisp, the meat is beefy and satisfying, but other than that, this specialty - which has been on the menu as long as any of the Montaños can remember - very closely resembles the taco served to more than 36 million customers every week at 5,600 Taco Bell locations in the United States. Coincidence? Mr. Arellano thinks not. In 1950, one Glenn Bell, an entrepreneur possessed by envy of the McDonald brothers" success, opened a burger stand across the street from Mitla (the building is still there; today, it's a taco stand). According to Mr. Arellano's research, Mr. Bell ate often at Mitla and watched long lines form at its walk-up window; later, having persuaded the Montaños to show him how the tacos were made, he experimented after hours with a tool that would streamline the process of frying the tortillas. He started serving his own tacos in 1951 (this according to Mr. Bell's 1999 biography "Taco Titan," which Mr. Arellano has practically memorized), and the business went through several name changes (Taco Tia, El Taco) before starting as Taco Bell in 1962. Now, at Mitla, the lines are gone; only the brown vinyl booths and the lunch regulars remain; while on the Taco Bell Web site, Mr. Bell is cited as the creator of the "fast food crunchy taco." The Montaño family members are philosophical about this outcome, but Mr. Arellano isn't. "There's a lot of anger about appropriations from Mexico, but in my opinion it's not enough," he said. The book tells many similar tales of white Americans (gabachos, he says, is the term Mexican-Americans use; gringo is now used only by gabachos) who have managed to capitalize on Mexican food, going back to the 19th century, when entrepreneurs in Texas raced to produce the first canned chili con carne. There is Duane Roberts, the son of a California butcher, who engineered the first frozen burrito; Henry Steinbarth, a German-American butcher, who first brought packaged chorizo to the national market; and George N. Ashley, who managed (briefly) to produce canned corn tortillas that seem to have been eaten mainly as a last resort by expatriate Southwesterners.