Yampa - Vermillion Ranch Sparks Res Feasibility Study_Final Report

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Vermillion Ranch Limited Partnership/Surface Water Impoundment 13659-RX the proposed dam location. Boulders, cobbles and clayey sand were observed in a road cut immediately south of the proposed dam. At the time of our subsurface exploration, Mr. T. Wright Dickinson owned the subject property. Vegetation near the proposed dam location is comprised of rgrasses used for agricultural grazing. Vegetation surrounding the area consists of native sagebrush and prairie grasses. A Site Location Map, Site Observation Sheet, and Test Boring Location Plan in Appendix A 1 describe the site in more detail. Geological Description Three major geological units were identified at the proposed dam location. rSoils within the Talamantes Creek floodplain and encountered along the proposed dam centerline consist of alluvial and fluvial sand, silt, and clay. These soils are products of bedrock in upland areas which have been weathered and loosely deposited along the Talamantes Creek drainage system during periods of seasonal runoff and flooding. These soils extended to a depth greater than 80 feet in one of the test borings (B-5). The northern embankment of the proposed earthen dam is comprised of claystone bedrock associated with the main body of the Wasatch Formation. Soils in this geological unit are generally weathered into their sand, silt, and clay constituents near the stratum surface and ' become less weathered with depth. The southern embankment of the proposed earthen dam and the proposed spillway location ' consists of poorly sorted clayey/silty sand with gravel deposits. These soils are considered to be old alluvial deposits remaining from the Talamantes Creek drainage system. As channel migration of the Talamantes Creek occurred, these soils remained to form an alluvial terrace. This stratum differs from alluvial deposits along the Talamantes Creek in that alluvium along the Talamantes Creek continues to be deposited and eroded with surface water runoff, whereas the old alluvial deposits along the southern dam embankment and spillway location are no longer subject to deposition or erosion of or by creek flow. Geologic units where derived from subsurface conditions encountered at the site and from the Geologic Map of the Vernal I' X 2° Quadrangle, Colorado, Utah, and Wyoming (Rowley, P.D., Hansen, W.R., Tweto, Ogden, and Carrara, P.E., 1985) distributed by the United States ' Geological Survey(U.S.G.S.). INBERG-MILLER ENGINEERS 4 February 26,2009