Laserfiche WebLink
• <br />Alluvial Vallev Floors <br />Introduction. An alluvial valley floor CAVE) analysis was performed by Keammerer <br />Ecological Consultants and Golder Associates, Inc. during the late summer and fall of 1990 <br />for Peabody Coal Company. The purpose of the study was to evaluate two of the drainages <br />in the vicinity of the Yoast Mine relative to their potential as alluvial valley floors. <br />The drainages that were evaluated include Sage Creek and Upper Grassy Creek. The study <br />area included the length of Sage Creek from upstream of the Yoast Mine to the railroad <br />embankment updreinage of the confluence of Sage Creek end the Yampa River and the length <br />of Grassy Creek from upstream of the Yoast Xine to Routt County Road 27. The lateral <br />extent of the study area was defined by the extent of valley fill and alluvial deposits. <br />Color aerial photographs (1"=1,000' scale), false color infrared photographs (1"=34,000' <br />scale), and USGS su rf iciel geology maps were utilized in addition to extensive field <br />checking. <br />Geomorahologv. A geologic deposits map (Exhibit 16-2) was constructed as part of the <br />geomorphic analysis. Six types of geologic deposits were identified along the stream <br />courses. These were anthropogenic fill, alluvium, valley fill deposits, fan deposits, <br />• coLluvium, end Landslide deposits. Anthropogenic fill (man-made) was used as the map unit <br />for some of the Larger earthfill embankments. Alluvium was mapped in areas where the <br />floodplain was broad and it was clear that feu of the deposits in the valley bottom were <br />related to the immediately adjacent valley slopes. Typically, the alluvium in the broader <br />floodplain areas contained more sand end gravel than was present in the valley fill end <br />other deposits. <br />• <br />Valley fill deposits, es used on the geologic map, comprise alluvium, colluvium, fan <br />deposits, end landslide deposits. In the upland areas along Grassy and Sage Creeks, the <br />valley bottoms consist of more then just alluvium, end hence [he term valley fill was <br />chosen. This usage is consistent wish the U.S. Geological Survey mapping of the area <br />(Madole, 1989). <br />Where possible, fan deposits were mapped based on the geometry of these geomorphic <br />features as observed on aerial photographs and field inspection. Fans are deposited in <br />this area at the mouths of intermittent tributary streams. <br />Lb-3-t Revised 06/19/95 <br />