As we bounce along an overgrown truck path in the dense brush country of South Texas’s historic San Vicente Ranch, the Longhorns we seek elude us beneath the midday sun. José “Che” Guerra, a rancher and collector of art and artifacts from colonial New Spain, is trying to show me cattle descended from a herd of wild Longhorns that his father began building in the fifties. But the animals are wary today. A couple of stragglers hear our approach and swiftly make their way deeper into the gray thickets of cenizo on the Guerra family’s ranch. “The Longhorns in Mexico were called criollos because they were born in the wild in the New World,” Che explains as we tour the ranch about thirty miles north of…