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Geography of the Eastern Plateau Planning Area

Figure 2.0-2 Eastern Plateau Planning Area

The Eastern Plateau Planning Area encompasses 26,700 square miles (sq. mi.) in the northeastern portion of the state. The planning area consists of one groundwater basin, the Little Colorado River Plateau Basin.  Counties and prominent cities, towns and places are shown in Figure 2.0-2.  The planning area is bounded on the north by the Arizona-Utah border, on the east by the Arizona-New Mexico border, on the south by the Mogollon Rim, and on the west by the Coconino Plateau Basin and Paria Basin in the Western Plateau Planning Area, whose boundaries coincide closely with U.S. Highway 89 (See Arizona Planning Areas Map).  The Mogollon Rim is an escarpment almost 2,000 feet high in some places, extending from central Arizona to the Mogollon Mountains in New Mexico.  It forms a hydrologic boundary between the Eastern Plateau Planning Area and the basins of the Central Highlands and Southeastern Arizona planning areas.  The Eastern Plateau Planning Area includes parts of four watersheds, which are discussed in  Section 2.0-2.  All of the Hopi Indian Reservation (2,534 sq. mi.), approximately 56% (14,680 sq. mi.) of the Navajo Indian Reservation, 2% of the Zuni Reservation (16 sq. mi.) and less than 0.2% of the Apache Reservation are located within the planning area. Ninety percent of the Navajo lands in  Arizona are located in the Eastern Plateau Planning Area. Many members of the San Juan Southern Paiute Tribe reside in several distinct communities located on the Navajo Reservation. The San Juan Southern Paiute is a relatively small tribe of approximately 265 members. The largest community is located at Willow Springs near Tuba City (ITCA, 2003).



Figure 2.0-3 Physiographic Provinces of Arizona

Physiographic provinces of Arizona

Data Source: Fenneman and Johnson, 1946

As shown in Figure 2.0-3 the planning area is almost entirely within the Colorado Plateau physiographic province, which covers the northern two-fifths of Arizona. This province is characterized by mostly level, horizontally stratified sedimentary rocks that have been eroded into canyons and plateaus, and by some high mountains.  Major mountain ranges are the San Francisco Peaks near Flagstaff, the White Mountains in the southeastern portion of the planning area and the Chuska and Lukachukai mountains located along the Arizona-New Mexico border (Figure 2.1-1).  The Chuskas reach an elevation of almost 10,000 feet and much of the rain and snow that falls in the Chuskas drains westward into Canyon de Chelly.  The Hopi Reservation is characterized by three mesas that rise to an elevation of 7,200 feet.  Elevations vary from 12,633 feet at Humphreys Peak near Flagstaff, the state’s highest point, to 4,200 feet at Cameron. The average elevation of the planning area is 6,061 feet.

Unique geographic features of the planning area include its relatively high elevation plateaus and mountains, steep cliffs, deeply incised sandstone canyons, and the painted desert consisting of multicolored badland hills and mesas that stretch across much of the mid-section of the planning area.  The southern boundary of the planning area marks part of the southern extent of the Colorado Plateau that occupies northern Arizona, northwestern New Mexico, eastern Utah and western Colorado. The Colorado Plateau is at least 500 million years old and has remained “structurally intact” while the surrounding Rocky Mountains and basin and range province were being formed. Huge amounts of sediment were deposited in the region which hardened into sedimentary rock several miles thick. (Grahame and Sisk, 2002)

Another geographic feature of the planning area is the relatively large number of volcanic cinder cones and peaks. Mt. Baldy in the White Mountains and the San Francisco Peaks are volcanic in origin and the San Francisco Peaks are considered potentially active. Sunset Crater northeast of Flagstaff erupted as recently as 1065 AD (Parra and others, 2006). Figure 2.0-4 shows the location of volcanic rocks in the vicinity of Flagstaff and the White Mountains, as well as other geologic information.

Much of the planning area is arid with few perennial or intermittent streams; however a significant number of perennial streams and lakes are found at higher elevations along its southern boundary, and the Colorado River defines the extreme northwestern boundary of the planning area (Figure 2.1-5). 


For more information on Geography in the Eastern Plateau Planning Area see Section 2.1.1 - Geographic Features


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