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• where Pine Gulch merges with Rattlesnake Gulch. It is not anticipated [ha[ mining in the <br />proposed lease modification area would affect this possible alltn-ial valley. However, final <br />determination will be made by Colorado DA9G during the review of the lessee's permit <br />application for the modification application area. <br />GEOLOGY AND b1INERAL RESOURCES <br />The only known mineral resource contained in the application area is coal. The coal deposits <br />occur within the Menefee Formation of the Cretaceous Mesa Verde Group and is within the <br />Durango Known Recoverable Coal Resource Area (KRCRA). <br />National King Coal is the only operating mine in the area at this time. There are no known oil <br />and gas deposits in the proposed modification area. However, oil and gas is known to occur in <br />the Point Lookout, Gallup, Dakota Sandstone and the Paradox Formations. <br />The proposed modification area is characterized by hilly plateau tops cut by one ephemeral <br />drainage. The elevation ranges from about 7,300 to 7,500. The geologic formation outcropping <br />in the area is the Cliff House Formation of the Cretaceous Mesa Verde Group and the overlying <br />Quaternary alluvial deposits. The coal proposed for mining is coal bed 1 in the Menefee <br />Formation that outcrops about 2 miles north ofthe proposed modification azea in the Hay Gulch <br />drainage. <br />No quantitative data exists for subsidence on the proposed modification area; however, the <br />surface effects of subsidence have been recorded on Federal leases P-058300, COC-29125 and <br />COC-49465 approximately'/,-mile north of the proposed modification area. The overburden <br />thickness ranges from 300 to 400 feet above coal bed 1 in the proposed modification azea. <br />Subsidence is directly affected by the thickness of the coal seam mined (4 to 6 feet), the <br />overburden thickness, and overburden composition. <br />A condition of approval of National King Coal's mine permit revision for Lease C-29125 and <br />subsequent permit revisions by Colorado Division ofMinerals and Geology was that subsidence <br />would be monitored on a quarterly basis. The purpose of the monitoring was to determine if any <br />new subsidence was occurring and if the Huntington Ditch was being affected in any way. <br />According to National King Coal records (Second Quarter Monitoring, 1999), there are no new <br />subsistence cracks in the azeas requiring monitoring. All areas, which lie above underground <br />support pillazs that have been removed, continue to be monitored on a quarterly basis for <br />evidence ofmaterial damage to the surface. <br />Colorado Division ofMinerals and Geology rules 2.05.6 and 4.20 require that "underground <br />nmining activities slmall be planned and conducted so as to prevent subsidence from causing <br />material damage to the surface." Material damage is defined in Rule 2.05.6 with respect to <br />• 6 <br />