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Consulting Engineers and Geologists <br />is approximately 1100 to 2000 feet (335.5 to 610.0 meters) in thickness. <br />Underlying the Williams Fork Formation is the Iles Formation which is com- <br />posed of sandstone, shale and coal. This formation is approximately 1500 <br />feet (457.5 meters) thick. <br />Seneca Coals Limited mines coal from the portion of the stratigraphic <br />column between the Twenty Mile Sandstone member of the Williams Fork <br />Formation and of the Trout Creek Sandstone member of the Iles <br />Formation. This part of the column is known as the Middle Coal Group. <br />Within this group there are three coal beds of economic interest, the <br />Lennox, the Wadge, and Wolf Creek coal beds. The Wadge coal bed is of <br />primary concern due to its uniform quality and thickness. <br />A yellow to red sandstone was encountered below the embankment during our <br />field drilling program. This sandstone was fine-grained quartz <br />moderately well cemented and according to the geologic map of the area, <br />belongs to the Williams Fork Formation (Miller, A.E., 1975, Geologic Map <br />of Routt County, Colorado - Map Series 1, Colorado Geologic Survey). <br />A more detailed geologic report was not attempted since Seneca Coals <br />Limited has detailed geologic informaton for the entire mine permit <br />area. <br />Seismic Activity. Soil and bedrock units are not expected to respond <br />unusually to seismic activity. The area has been classified as Zone 1 <br />risk area (Algermissen & Perkins, 1976) that can expect only minor <br />damage from earthquake of intensities V or VI on the Mercalli Scale. <br />Maximum bedrock accelerations of 5 percent gravity are probable accord- <br />ing to Algermissen & Perkins, during major earthquake events. <br />-3- <br />