2010-05-07_PERMIT FILE - C2009087A (4)

Home Browse Search

• whether a substantial probability exists that given its known habitat requirements it could occur in the project area. GENERAL HABITAT COMPARISONS Many of the species in Table 23 are found in western Moffat and Rio Blanco Counties though mostly at lower elevations and further west than the Study Area. Many of these require seepy sandstone cliffs not found in the Study Area, and many occur on outcrop sites where active weathering / erosion keeps soils thin and competition low. Areas in the Piceance Basin (aka the Roan Plateau) are characterized by high plateaus and deep valleys, and possess younger geology including lacustrine shales of the Tertiary (Eocene) age Wasatch, Green River and Uinta Formations composed of oil shale, sandstone and siltstone. As a result, the soils of these areas are derived from sediments from ancient salt lakes. This depositional environment may be responsible (via details of salt content) for making them ideal refuges from competition for T &E plant species. Many of these species are known to occur at lower elevations and in areas with much lower average annual precipitation than the Study Area. Given that many of the rare species involved are, in effect "fugitives from competition," the same substrates in higher moisture • conditions are likely to support more plant growth and competition. In contrast, the surface environments of the Sage Creek Underground Baseline Study Area in western Routt County are characterized by outcroppings of materials of the Williams Fork Formation (middle Upper Cretaceous -age, Mesa Verde group) along with the overlying Lewis shale (Upper Cretaceous). The Williams Fork Formation contains a variety of shale, sandstone and coal beds, while the Lewis Shale is marine in origin. Within the study area, the Lewis Shale materials are comprised of relatively less clay and more silt than often is the case for marine shales. As a result, upon weathering, the material produces a soil parent material of sufficiently moderate texture to form soils that are, or have been, cultivated for small grains, leaving little chance for the continued presence of native plant species. The upper -most member of the Williams Fork Formation, the Holderness member is comprised of interbedded sandstones and shales that tend to support the heavy growth of mountain brush (oak, serviceberry, chokecherry). Because of the substantial differences in geology (and often in elevation and moisture conditions) between the Study Area and the Piceance Basin of northwest Colorado, it is unlikely that any of the T &E species that are found there would be found in the Study Area. The Study Area in general is characterized by much denser vegetation including sagebrush, aspen, conifer and • 26