Tucson, city, seat (1864) of Pima county, southeastern Arizona, U.S. Tucson lies along the Santa Cruz River on a hilly plain of the Sonoran Desert that is rimmed by the Santa Catalina and other mountains. The city lies at an elevation of 2,410 feet (735 metres) and is situated about 115 miles (185 km) southeast of Phoenix. In 1692 the Jesuit missionary Eusebio Kino first visited the Tohono O …