Geography of the Southeastern Arizona Planning Area

The Southeastern Arizona Planning Area encompasses 16,072 square miles (sq. mi.) of geographically diverse groundwater basins in the southeastern corner of Arizona. Groundwater basins include: Aravaipa Canyon, Bonita Creek, Cienega Creek, Donnelly Wash, Douglas, Dripping Springs Wash, Duncan Valley, Lower San Pedro, Morenci, Safford, San Bernardino Valley, San Rafael, Upper San Pedro and Willcox.  Basin boundaries, counties and prominent cities, towns, and places are shown in Figure 3.0-2.

The planning area is bounded on the east by New Mexico, on the south by the international boundary with the state of Sonora, Mexico, on the west by the Active Management Area (AMA) Planning Area (Phoenix, Pinal, Santa Cruz and Tucson AMAs) and on the north by the Central Highlands Planning Area and a small portion of the Eastern Plateau Planning Area.  The planning area includes parts of 5 watersheds, which are discussed in Section 3.0-2.  Most of the 2,900 sq. mi. San Carlos Apache Reservation, (83.1% or about 2,400 sq. mi.), is located in the north central part of the planning area.

Figure 3.0-2  Southeastern Arizona Planning Area

Figure 3.0-3 Physiographic Provinces of Arizona

The majority of the planning area is within the Mexican Highland section of the Basin and Range physiographic province, which is characterized by northwest-southeast trending mountain ranges separated by broad alluvial valleys (see Figure 3.0-3). The Mexican Highland section is a higher elevation area of the province with valleys ranging from 2,500 to 4,000 feet above sea level and mountains and valleys covering about equal areas. The extreme northern portion of the planning area falls within the Central Highlands transition zone, which is characterized by rugged mountains of igneous, metamorphic and sedimentary rocks.  The average elevation in the planning area is 4,500 feet.  Elevation ranges from 10,713 feet at Mount Graham in the Pinaleño Mountains in the Safford Basin to 1,830 feet near Kearny where the Gila River exits the planning area in the Lower San Pedro Basin.

A unique feature of the planning area is mountain ranges that are isolated from each other by valleys of desert grasslands and desert scrub. These “sky islands” are part of a unique complex of about 27 mountain ranges in Arizona, New Mexico, and the Mexican States of Sonora and Chihuahua. 

The southwestern sky island complex extends from subtropical to temperate latitudes, a condition found nowhere else. (Warshall, 2006) The highest elevation sky islands are the Pinaleño Mountains found along the Safford/Willcox/Aravaipa Canyon basin boundary and the Chiricahua Mountains along the southern Willcox and Safford basin boundary.  The planning area transitions to one of Arizona’s major mountain ranges, the White Mountains, along the northeastern boundary.

The planning area includes drainages of the San Pedro River and Upper Gila River. The Gila River originates in western New Mexico and enters Arizona near Duncan in the Duncan Valley Basin.  The river generally flows west through the Safford Basin. The San Pedro River flows north from Mexico through the Upper and Lower San Pedro Basins and joins the Gila River at Winkelman. Surface water in the planning area flows into the Gila River except for the Willcox Basin, a “closed basin” with internal drainage, and several basins where drainage flows south into Mexico. These basins are the Douglas, San Rafael and San Bernardino Valley basins. The Santa Cruz River originates in the San Rafael Basin, flows south into Mexico, turns north and enters the Santa Cruz AMA east of Nogales.

For more information on Geography see individual basins in the directory to the right.

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