 The first Spanish mission call the settlement variously as "La Tía Juana", "Tiguana", "Tiuana", "Tiwana", "Tijuan", "Ticuan", as well as "Tijuana".While the Mexican city standardized to "Tijuana", the American term for both the river and a U.S. settlement which is now part of San Ysidro remained "Tía Juana" until the mid-20th century.The commonly accepted theory among historians is that "Tía Juana", as Argüello named his rancho, is derived from the word ("by the sea") in the language of the Kumeyaay—the original aboriginal inhabitants of the San Diego-Tijuana region.