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Throughout the Northern Southwest, the marked increase in precipitation during late summer is caused by <br />a monsoonal circulation pattern. This pattern originates when the hemisphere warms up in summer and <br />shifts the westerlies and sub -polar lows northward. This places a high pressure cell (the Bermuda High) <br />over the central United States. The western edge of the Bermuda High rotates clockwise sending <br />moisture laden air into the Southwest from the Gulf of Mexico. The convective air currents created by <br />the hot lowland deserts and the convergence of the moist air masses with the cooler highland air often <br />creates powerful afternoon thunderstorms from mid to late summer (Sellers and Hill 1974; Gillispie 1985: <br />14-15). <br />Surface geology in the project consists of glacial outwash and loess deposits on mesa tops overlying <br />sandstone and shale members of the Cliff House Sandstone of the Mesaverde Group. The Cretaceous <br />Cliff House Sandstone overlies the Menefee Formation, which contains carbonaceous shale often <br />associated with coal deposits. The Cliff House Sandstone is a transgressive shallow marine deposit from <br />shore faces of a barrier island beach front (Aubrey 1991: B13). The glacial outwash deposits in the <br />project vicinity are localized and date to the early to middle Pleistocene and consist of diorite/monzonite <br />porphyry, sandstone and siltstone, granitic rocks, and chert gravels and cobbles with few boulders (Scott <br />and Moore 1981). Soils in the project area consist of reddish brown silt loam to clay loam calcareous <br />loess at MW -2, MW -3, and MW -4. Soils at the MW-HGA4 location are alluvial but also consist of <br />reddish brown clay loam. <br />3.2 Vegetation <br />With the exception of the proposed MW-HGA4 location, which is situated in an irrigated pasture, <br />vegetation in the project area is characterized by Great Basin conifer woodland habitat. Vegetation cover <br />generally ranges from 30 to 70 percent. Woodland overstory composition consists of mature to old <br />growth stands of Colorado pifion pine (Pinus edulis) and Utah juniper (Juniperus osteosperma) trees with <br />occasional Rocky Mountain juniper (Juniperus scopulorum) trees, while dense stands of big sagebrush <br />(Artemesia tridentate) characterize desert scrubland openings. The woodland understory is generally <br />dominated by various shrubs, such as Gambel oak (Quercus gambelii ), mountain mahogany <br />(Cercocarpus montanus), cliff fendlerbush (Fendlera rupicola), wild crabapple (Peraphyllum <br />ramosissimum), mountain snowberry (Symphoricarpos oreophilus), black sagebrush (Artemisia novum), <br />big sagebrush (Artemesia tridentata), and antelope bitterbrush (Purshia tridentata). Understory <br />herbaceous species typically include Indian ricegrass (Oryzopsis hymenoides), Richardson's bitterweeed <br />(Hymenoxys richardsonii), linaria penstemon (Penstemon linarioides), silvery lupine (Lupinus <br />argenteus), bottlebrush squirreltail (Elymus elymoides), Junegrass (Koeleria macrantha), muttongrass <br />(Poa fendleriana), redroot buckwheat (Eriogonum racemosum), basin prickly pear (Opuntia macrorhiza), <br />and banana yucca (Yucca baccata). <br />An Intensive CRI for GCC Energy's Proposed Groundwater Monitoring Wells <br />on State and Private Lands in La Plata County, CO <br />SEAS 16-098 October 2016 <br />6 <br />