Sentinel Peak is a 2,897 ft peak in the Tucson Mountains southwest of downtown Tucson, Arizona, United States. The valley's first inhabitants grew crops at the mountain's base, along the Santa Cruz River. The name "Tucson" is derived from the O'odham Cuk Ṣon, meaning "the base is black". In the 1910s, University of Arizona students used local basalt rock to construct a 160 ft tall block "A" on the mountain's east face, near its summit, giving the peak its other name, "A" Mountain.