Tohono O’odham peoples inhabited southern Arizona’s Sonoran Desert valleys, relying on saguaro fruit, prickly pear, mesquite bean pods and cultivated sugar cane, beans and squash, long before Spanish explorers first arrived in the late1500s. Missions were established in the region early on—San Xavier del Bac, south of Tucson, dates to 1692, and the nearby Spanish fortress, Presidio San Agustín del Tucson, was built in 1775. The presidio and surrounding town remained part of Mexico until the United States gained control of the territory in 1854. A center for trade and commerce during the Wild West era of Wyatt Earp and the Clanton gang (Earp gunned down presumed outlaw Frank Stilwell near the Tucson train station in 1882), Tucson was incorporated in 1877, and further boosted by the arrival of the Southern Pacific Railroad in 1880. The University of Arizona, the state’s oldest, was formed in 1885. Arizona’s winter warmth, dry climate and intriguing deserts started drawing tourists in the late 19th century, including World War I veterans who needed respiratory therapy after being gassed on the battlefields of Europe. Modern-day inheritors of that health-vacation heritage are the many resort spas that welcome Tucson visitors, including Canyon Ranch, whose founding in 1979 helped inaugurate the modern health spa industry in the United States. Today the Tucson metro area (Pima County) has over 1 million residents, and draws 4 million visitors a year.