Visitors to the southwestern states are often surprised by the Spanish or, more recently, Mexican presence. In posh neighborhoods of 1910 or 1940 vintage, houses stagger under red tile roofs and squint from iron-grilled windows. Church facades have accumulations of twisted columns, multiple cornices, and bracketed niches. Tacos are served from arcaded, stone portals, with a mission bell nearby. On the air, a brass combo slips in a little "salza," or even a paso doble. Reality outdoes Hollywood. Some visitors revel in it; others reject it as phony. Is there a significant Spanish presence in this land, or rather, where is it?

Beneath the ...