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2023 Cultural Resource Site Assessments for Collom Expansion Project Colowyo <br />Tetra Tech June 2023 3 <br />For Official Use Only: Disclosure of Site Locations Prohibited (43 CFR 7.18) <br />1.1 Environmental Setting <br />The Collom project area is situated in the Southern Rocky Mountain physiographic province <br />(Fenneman 1931; Thornbury 1965). The province is described as a series of uplifts that occurred <br />between 300 million years ago and 60 million years ago. The project area is among a series of <br />long, broad, northeast/southwest-trending ridges that originate in the Danforth Hills and end at <br />the Axial Basin in the north (Figures 2 and 3). Elevations range from 6,500 feet (1,981 m) in the <br />north to 8,567 feet (2,611 m) in the south. The Danforth Hills are a series of uplifted folds that <br />structurally connect the Uinta Mountains to the west with the Rocky Mountains to the east <br />(Fenneman 1931; Thornbury 1965). The Axial Basin is the southernmost extent of the Wyoming <br />Basin. The basin is a highly eroded anticlinal trough. <br />The project area geology is composed of Williams Fork sandstone, shale, and coal beds. Iles <br />Formation sandstone and shale occur along the margin of the Axial Basin. Surface sediments are <br />variable depending on the location within the project. In addition to sandstone outcrops, upland <br />sediments are typically a mix of residuum and colluvium sand loam with regolith gravels. <br />Sedimentary deposition is generally shallow in the upland areas. Lowland and drainage bottom <br />sediments are typically alluvial silt loams with varyingly dense pebble- to boulder-size gravels. <br />The lowland sediments tend to be much deeper than upland areas. <br />Climatically, the upland areas have a highland climatic regime, and the lowland areas have a <br />continental steppe climate. Annual precipitation exceeds 30 inches (76 cm) in the upland areas <br />and averages between 20 and 30 inches (50 and 76 cm) in the lowland areas. Climate, <br />precipitation, and elevation determine vegetation communities. The dominant vegetation <br />community is sagebrush, rabbitbrush, wheatgrass, wild rye, and prickly pear cactus. Higher <br />elevation communities are similar with varying densities of oak brush and aspen. Riparian <br />vegetation communities are the second most common within the project. Along the drainage <br />bottoms, natural springs, and man-made features are willow, cattail, broadleaf cottonwood, and <br />various grasses. <br />Fauna in the project area ranges from large ungulates like mule deer, antelope, and elk to small <br />mammals including rabbits, porcupines, greater sage grouse, and various small rodents. Coyotes, <br />black bears, and mountain lions are also reported to inhabit the region. <br />1.2 Present Built Environmental Setting <br />The Collom Project and vicinity has been utilized for various activities associated with recreation, <br />homesteading, hay farming, coal mining, and livestock grazing. During the historical era, <br />numerous homesteads and small coal mining operations existed within the project area. In the <br />modern era, the private lands within the Collom area are owned and managed by Colowyo. <br />Colowyo permits various levels of livestock grazing and hunting on the land. Any other land use <br />is in support of Colowyo’s current mining operations and/or toward the development of the Collom <br />area. In 2017, construction on the haul road, facilities, and pit commenced and was mostly <br />completed in 2018. The Collom pit and associated facilities are now operational.