3.0 Affected Environment
3.0 Affected Environment 3.1 Geologic Setting 3.1.1 Geology The Navajo Nation lies entirely on the Colorado Plateau, and is composed of a variety of geologic features including canyons, mesas, barren badlands, and expansive flatlands (Foos 1999). The Colorado Plateau covers an area of approximately 130,000 square miles, covering western Colorado, northwestern New Mexico, southeastern Utah, and the northern Arizona. Land surface elevations within this area can range from 5,100 feet above sea level on the western side to over 10,000 feet within some of the mountain ranges found within the project area. The region is rich with geologic history through plateau uplift, deposition, and hydrologic erosion, giving rise to the unique features and landscape of the Southwestern United States. Specifically, the Navajo Nation lies mainly on the Navajo Section of the Colorado Plateau, with some territory on the Grand Canyon and Datil Sections (Rigby 1977). Major geological formations found on the Navajo Nation include the Chuska and Carizzo Mountains, Defiance Plateau, and the San Juan Basin in the eastern portion of the region (Figure 3-1). The Chuska Mountains and the Defiance Plateau are part of the same monocline region, separated by the Black Creek Valley. The uplift is formed from volcanic and sedimentary rocks with geologic layers ranging from the DeChelly Sandstone through the Chuska Sandstone formations with Defiance Plateau lying between 7000 to 8000 ft in elevation and the Chuska Mountains reaching over 10,000 ft in elevation (Harshbarger and Repenning 1954, Peirce et al. 1979). The San Juan Basin located near Farmington is a major coal source thanks to the prominent Fruitland Formation that borders the outlying portions of basin (Fassett 2000).
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