||This article needs additional citations for verification. (May
2011)| Although Southern Arizona's boundaries are not well-
defined, it is generally considered to include all areas south
of the Gila River but sometimes only Cochise County, Pima County
and Santa Cruz County, anchored by the city of Tucson. Other
cities and large towns in Southern Arizona include Ajo, Casa
Grande, Gila Bend, Sierra Vista, Yuma, and the border cities of
Nogales and Douglas Southern Arizona is the location of several
large National Monuments protecting the scenery, wildlife, and
archaeological sites of Southern Arizona, and the Saguaro
National Park, which stands on two large sections of land, one
west of the Tucson metropolitan area and the other one east of
Tucson. Sometimes, Southern Arizona is considered to include the
Phoenix Metropolitan Area, also. To some authorities, the
northern boundary of Southern Arizona can be considered to be
the Gila River, which sometimes flows west to the Colorado
River, downstream of the Scotts