FROM here to Tierra del Fuego, carne asada means grilled meat. But the smells wafting from backyard grills in this desert area, where the climate makes it nearly a year-round method of cooking, are distinctive.Locally, instead of throwing unmarinated meat on the grill, butchers have developed a lemon-and-water-based marinade spiced with chili powder, oregano, cumin, pepper, salt, onions, and whatever else the cook decides to throw in. Corner grocer Bobby Gallegos explains that in 1972 a local meat distributor was selling surplus "throwaway" meat called skirt steak. He told Mr. Gallegos how other local butchers were using a lemon-based marinade to sell it. So Mr. Gallegos developed his own nine-spice seasoning and 3 to 1 (water to lemon juice) marinade for the thin skirt-steak carne asada. It has become so popular that he sells 500 to 600 pounds of it a week out of his small store and no longer offers anything but carne asada. The skirt-steak cut and patience, says mustachioed Gallegos, are the keys to carne asada. "The longer you let it sit and the thinner you cut it, the better it tastes," he says, as he butterflies a long skirt of meat from a half-inch thickness to one-quarter inch. He won't discuss what's in his spice mix, noting that when those who move away from the area can't come up with their own recipe they send for his carne asada. He's shipped packages of the meat to weddings, parties, and those just fondly remembe ring the carne asada taste from San Diego, Calif., to Orlando, Fla.