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Active Management Area Geography

The AMA Planning Area covers approximately 14,700 square miles and stretches continuously from the international border through central Arizona to the northern boundary of Maricopa County. The most northern AMA, the Prescott AMA, is discontiguous from the other four AMAs (Figure 8.0-2) and is within the boundaries of the Central Highlands Planning Area, which borders the Phoenix AMA on the north. The planning area is located between the Southeastern Arizona Planning Area on the east and the Lower Colorado River Planning Area on the west and includes portions of six watersheds, which are discussed in section 8.0-2, Surface Water Hydrology

Most of the AMA Planning Area is located in the Basin and Range physiographic province, which is characterized by broad, gently sloping alluvial basins separated by north to northwest trending fault-block mountains (Figure 8.0-3).  The Prescott AMA and a small portion of the Phoenix AMA lie within the Central Highlands transition zone, which is characterized by a  band of mountains of igneous, metamorphic, and sedimentary rocks.  Because of its geographic extent and location in the state, the planning area exhibits a wide range of geographic features, from low elevation, broad, semi-arid Sonoran desert valleys to mountain ranges with summits over 9,000 feet. The topographic variability results in broad variations in the amount of precipitation, temperature range and vegetation type.

At approximately 485 square miles in area, the Prescott AMA is the smallest AMA basin and has the highest average elevation, ranging from 4,400 feet in the valleys to approximately 7,800 feet in the Bradshaw Mountains. The AMA is characterized by rolling topography, broad sloping alluvial basins and fault block mountains (see Figure 8.3-1).  Streamflow in surface drainages are primarily ephemeral or intermittent.


Click to view Figure 8.0-2

Figure 8.0-2 Active Management Area Planning Area

Figure 7.0-3

Figure 8.0-3 Physiographic Provinces of Arizona

The Santa Cruz AMA is approximately 716 square miles in area.  It lies adjacent to the international border and its major drainage, the Santa Cruz River, flows from Mexico into the basin. The AMA is characterized by the relatively narrow river drainage flanked by hills and higher elevation mountains on its northern, eastern and western boundaries. Elevations range from 3,000 feet where the Santa Cruz River exits the basin to over 9,400 feet in the Santa Rita Mountains (see Figure 8.4-1). 

North and west of the Santa Cruz AMA, the Tucson AMA is approximately 3,866 square miles in area with two major, parallel alluvial valleys, the Upper Santa Cruz in the east and the Avra and Altar valleys in the west. The Santa Cruz River drains the Upper Santa Cruz Valley and is the major drainage in the AMA. Mountain ranges form the eastern and southern borders of the AMA.  These “sky islands” are relatively isolated ranges separated by valleys that are part of a unique complex of mountains that are also found in northern Mexico and New Mexico (Warshall, 2006).  The Tucson AMA has the widest elevational range of any of the AMAs with elevations ranging from 1,770 feet north of Picacho Peak, to over 9,400 feet in the Santa Rita Mountains (see Figure 8.5-1).

The Pinal AMA is located to the north and west of the Tucson AMA, and at 4,100 square miles in area, is the second largest basin in the planning area. It is characterized by broad, alluvial Sonoran desert valleys and mid-elevation north to northwest trending fault-block mountains. The Gila River flows east to west in the northern part of the basin while the Santa Cruz River enters the basin from the southeast, flowing primarily ephemerally toward the northwest.  Elevations range from about 1,000 feet where the Gila River and Santa Cruz River exit the basin in the northwest to over 6,800 feet at Kitt Peak at the southern basin boundary (see Figure 8.2-1).

The Phoenix AMA is the largest AMA basin at approximately 5,646 square miles and is characterized by Sonoran desert valleys that are generally from 1,000 to 2,500 feet above mean sea level, surrounded by mid-elevation mountain ranges. The basin is drained by five major rivers, the Salt, Gila, Verde, Agua Fria and Hassayampa. The state’s most important water producing watersheds, the Salt and the Verde, converge in the Phoenix AMA, representing an important water supply for the area. Elevations range from 755 feet where the Gila River exits the basin to almost 5,900 feet in the New River Mountains on the northern basin boundary (see Figure 8.1-1).


water drop  Continue to Section 8.0.2 - Hydrology: Groundwater


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