While cactus occur in other parts of the west, it is in the southern third of Arizona where they reach their most magnificent, forming veritable forests that stretch for miles. This is where Saguaro National Park is located, protecting two areas of prime cactus landscape, one on either side of the city of Tucson. Further south Organ Pipe Cactus National Monument features an almost lush landscape covered with many types of cactus, featuring its namesake species.
The western part of this region slopes down to the Colorado River, a chain of reservoirs, dams and diversions for agricultural and urban use. This is the Colorado Desert, close to sea level, very dry, and one of the hottest places on earth. Vast empty spaces spread east from the river: desert rangeland, wildlife refuges, the Tohono O'Odham Nation (Indian reservation), and a huge military bombing range. It is one of the least populated parts of the U.S.
Abrupt small mountain ranges are scattered across this entire region, their cooler wetter climates supporting ecosystems that differ dramatically from the surrounding lowlands, truly biologic islands in a sea of desert. Though Tucson is the hottest major city in the country, there is a ski resort on Mount Lemmon just to the north.
The region's Spanish heritage is represented by the Mission of San Xavier del Bac near Tucson, known as the white bird of the desert, and further south the ruins of Tubac Presidio and Tumacacori Mission. The Mexican border, recently fenced and heavily patrolled, is punctuated by busy crossing points at the twinned cities of San Luis/San Luis Rio Colorado, Nogales/Nogales, and Douglas/Agua Prieta.
Copper and other mines dot this landscape, along with picturesque old-fashioned mining towns like Bisbee, and the fabled semi-ghost town of Tombstone. There are also huge open pit mines and the unique company town of Ajo.
The southeast corner of the state includes the dramatic rock formations of Chiricahua National Monument, and historical traces of the Apache tribe and its last stand against white domination. Coronado National Memorial honors Francisco Vasquez de Coronado, who came through this area in the 1540's searching for the legendary Seven Cities of Gold.