The first Native Americans arrived in Arizona between 16000BC and 10,000 BCE, while the history of Arizona as recorded by Europeans began when Marcos de Niza, a Franciscan, explored the area in 1539. Coronado's expedition entered the area in 1540–1542 during its search for Cíbola. Padre Eusebio Francisco Kino developed a chain of missions and taught the Indians Christianity in Pimería Alta (now southern Arizona and northern Sonora) in the 1690s and early 1700s. Spain founded fortified towns (presidios) at Tubac in 1752 and Tucson in 1775.All of present-day Arizona became part of the Mexican State of Vieja California upon the Mexican assertion of independence from Spain in 1821. The United States took possession of most of Arizona at the end of the Mexican–American War in 1848. In 1853, the land below the Gila River was acquired from Mexico in the Gadsden Purchase. Arizona was administered as part of the Territory of New Mexico until it was organized into a separate territory on February 24, 1863.