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). In the western portion, Marble Canyon and Echo Cliffs run down from Navajo Nation border with the Grand Canyon. Marble Canyon and Echo Cliffs run along a tributary of the Colorado River from Lee’s Ferry to the Little Colorado River. The canyon is a prominent monocline, exposing cliffs from the Moenkopi and Chinle Formations. Black Mesa, a prominent mesa in the northern center of the region, rises over 8000 ft in elevation as a Cretaceous island formed from folded geologic layers and topped with soils derived from geologic layers ranging from the Dakota formation to Mesaverde sandstone (Nations et al. 2000). In the north, Navajo Mountain is a prominent laccolith, formed from igneous rock intruding into sedimentary substrate layers towering over 10,000ft in elevation. Shiprock, a prominent monadnock located near the town of the same name, is part of a field of the Chuska Volcanic Field, which is collection of similar geologic features that remain from an ancient volcano that previously existed in the area (Crumpler 2015). 65 Figure 3-1. Map of bedrock geology for the Navajo Nation. Geologic layers are based on the King and Beikman map for the United States (1974) with modifications to labeling nomenclature to reflect regional stratigraphic layers and group names per USGS mapping efforts 66 The Navajo Nation is rich with geologic history, allowing geologists to view and study a variety of geologic layers and events that helped shaped this unique landscape (Figure 3-2). Bedrock layers for the region can range from Pre-Cambrian gneiss to Quaternary alluvium. Prominent formations within this layer include the Supai formation, Coconino Sandstone, and Kaibab Limestone. Mesozoic rock layers were formed mostly through depositional inputs over time and are mostly composed of sandstone and shale. Key formations within this group of geologic layers include the Moenkopi Formation, the Chinle Formation, the Kayenta Formation, Navajo Sandstone, and the Mesaverde group. Cenozoic rock layers are formed from igneous intrusion, volcanic rock, and gravel. Finally, many portions of the Navajo Nation have significant cover from quaternary deposits, including eolian sand dunes and alluvial deposits (Figure 3-3). Surface geology on the Navajo Nation is also important for understanding the geologic history of the area as well as the vegetation communities and species that are currently present. These components are where much of the existing soils are derived and can provide information on major forces that help shape the landscape of the Navajo Nation today. Much of the region is covered with broad alluvial valleys, where rivers and waterways carried fine grained sediments during the Holocene, which are most apparent near the Colorado and Little Colorado River Valleys, the Black Mesa region, San Juan Basin, and Chaco Canyon (Andrews 1991). While alluvium deposition is still a major source for sedimentation and soil genesis near streams, rivers, and washes, nearly a third of the Navajo Nation is covered with eolian sand, or wind distributed sediments (Muhs and Been 2004, Redsteer et al. 2010). Recent changes in climate have caused drier conditions resulting in decreased vegetative cover and an increase in the transport of eolian sand dunes within the region, facilitating dune formation and migration within the region. Additionally, these changes further encourage the replacement of perennial grasses with annual species, such as Russian thistle, which only provide temporary stabilization of eolian deposits and soils, contributing to increasing dust storms and loss of top soil on the Navajo Nation (Draut et al. 2012). 3.1.2 Mineral Resources Due to the unique geologic setting of the Navajo Nation, the area has several mineral resources that have been mined and extracted within the area. Mineral deposits are highly linked to the varying geologic layers found within the Navajo Nation. The development of different extraction industries for mineral resources has been rife with controversy on the Navajo Nation, much of it from the results of environmental and public health impacts to surrounding communities. 67 Figure 3-2. A stratigraphic chart of major geologic layers that can occur on the Navajo Nation, with younger layers at the top and older layers at the bottom. This chart is not scaled to for geologic time and the presence of different geologic layers varies across the region. Numbers on the chart denote layers where resources such as 1uranium, 2coal, 3oil, and 4methane can potentially exist. Colors correspond with the geologic bedrock layers described in Figure 3-1. 68 Figure 3-3. Surficial geology of the Navajo Nation as developed by the Southwestern Regional Gap Analysis Project (USGS 2005). Surficial data was compiled from geologic maps from Arizona (Hirschberg and Pitts 2000), New Mexico (Green and Jones 1997), and Utah (Ramsey 1996) to develop a generalized map for the region. 69 The most famous and controversial of mineral industries was the uranium mining that occurred on the Navajo Nation from the 1940’s through the mid-1980’s. Sandstone deposits, such as the Shinarump member of the Morrison, Chinle, and Moenkopi Formations, are the geologic layers where uranium is most abundant in the Navajo Nation (Repenning et al. 1969, Chenoweth 1993, Billingsley et al. 2007, TerraSpectra Geomatics 2007). In the 1940’s the discovery of uranium deposits in the region and the threat of the Cold War, led to the widespread establishment of uranium mining operations. While mining operations slowed around the mid-1960s and stopped altogether in the mid 1980’s, the remains of hundreds of abandoned mines and mine waste has left major impacts on the Navajo people, leaving many communities and workers to deal with the impacts of increased radiation exposure and illness (USEPA 2013). As a result of such actions, the Navajo Nation passed a legal ban on uranium mining through the Diné Natural Resources Protection Act of 2005 (18 N.N.C. §1301) Uranium mining occurred across the Navajo Nation in six areas, which have been designated by the U.S. Environmental Protection Agency (U.S. EPA) as abandoned uranium mine regions where mining operations were concentrated (Figure 3-4). While similarly named, these mining regions are not related to the Navajo Agencies. On the Western Abandoned Uranium Mining Region, major mining was concentrated in Cameron, although mining operations occurred from Bitter Springs in the North to Grand Falls in the south and as far east as Ward Terrace. The Morale Mine in the Hopi Buttes was the only productive mine in operation in the Southern Abandoned Uranium Mining region. The Central Abandoned Uranium Mining Region had several mines on the east side of Black Mesa, with a few located near Rough Rock. In the North-Central Abandoned Uranium Mining Region, mining occurred in Monument Valley along the Arizona-Utah border with the Whirlwind mine on the San Juan River. For the Northern AUM Region, mining operations were conducted around the Carrizo Mountains with a few straddling the Arizona-New Mexico border and the Cove Mesa mine located further south near the Lukachukai Mountains. In New Mexico, a few mines in the region were also in the Sanostee region. The Eastern Abandoned Uranium Mining Region saw mining operations in the productive Grants Uranium District, stretching from Church Rock in the west to Ambrosia Lake in the east (USEPA 2013). To date, the U.S. EPA has identified over 500 different abandoned mine locations on the Navajo Nation (USEPA 2013). Clean-up efforts are coordinated and implemented in the region by the U.S. EPA, the Navajo Nation EPA Superfund Program, and the Nuclear Regulatory Commission, with additional funding provided by Anadarko Petroleum and Kerr-McGee Corporation as the result of Department of Justice settlement in 2014 (USEPA 2013, USDOJ 2014). However, the recent increase in demand for uranium oversees has increased pressure on the Navajo Nation to permit uranium mining once again. Several mining companies have purchased mining rights to lands and rights-of-way located on the Navajo Nation and have been seeking approval to conduct mining operations in the area.

Load more