How has the arizona-sonoran region developed a separate identity that is neither american nor mexican?

 The Arizona-Sonora Border:
Line, Region, Magnet, and Filter. . . Belonging truly to neither nation, it serves as a kind of cultural buffer zone for both, cultivating its own culture and traditions. Like other borders, it both attracts and repels. Like them, it is both barrier and filter. It is above all a stimulating cultural environment. . . .--James S. Griffith
The Arizona Sonora border was established as a result of the Gadsden Purchase of 1853. It runs through desert and mountain country, from the western Chihuahuan Desert by New Mexico through a zone of grassland and oak-covered hills to the classic Sonoran Desert west of Nogales. The land gets more and more arid as one travels west, and the western third of the border is essentially devoid of human habitation. It is this stretch of the border, once a major road to the Colorado River, that has earned and kept the title El Camino del Diablo, "The Devil's Highway."

Yes all of them are right