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2.04.6 -GENERAL GEOLOGY DESCRIPTION
<br />LOCAL GEOLOGY
<br />The local area is characterized by southerly dipping, sedimentary rocks of
<br />cretaceous age which have been deeply eroded to the north.
<br />The uppermost formation exposed locally is the Cliff House Formation, which
<br />is the upper member of the Mesa Verde Group. It is of marine origin and is
<br />composed of irregular to lenticular ledges of hard, fine to medium grained,
<br />calcareous sandstone in softer argillaceous fine sandstone, mudstone and silty
<br />shale. The top of this formation has been removed by erosion, leaving an average
<br />thickness of 350 feet. The Cliff House Formation overlies the Menefee Formation.
<br />The Menefee Formation, which is the middle member of the Mesa Verde Group
<br />is composed of a complex assemblage of cross-bedded sandstones, black shales and
<br />coal beds. Up to seven coal seams have been identified by the U. S. Geological
<br />Survey. The Menefee Formation has an average local thickness of 300 feet. The
<br />Menefee overlies the Point Lookout Formation.
<br />The Point Lookout Formation, which is the basal member of the Mesa Verde
<br />Group, is divided into two parts. The upper member consists of thick, massive beds
<br />of even-textured, medium-grained sandstone. The lower member consists of thin
<br />sandstone beds with the Mancos Shale below. The Point Lookout Formation has an
<br />average local thickness of 400 feet.
<br />The Mancos Shale, which is exposed approximately four miles north of the
<br />King I Mine, is of marine origin and composed of dark-gray to black shale and silty
<br />to fine sandy shale with small amounts of dark-gray argillaceous limestone in
<br />lenses. The Mancos Shale has an average local thickness of 2000 feet.
<br />The bedding of the above sedimentary rocks dips 2~ to 11~ in a southerly
<br />direction, flattening to the south.
<br />STRATIGRAPHY
<br />The Hesperus area, located on the northwestern flank of the San Juan Basin,
<br />contains rocks of Quaternary and Cretaceous age. The Quaternary sediments are
<br />confined to the valley bottoms and in particular the La Plata River valley along the
<br />eastern portion of the area. These deposits are primarily poorly consolidated gravels.
<br />The Cretaceous rocks exposed in the project area consist of Mancos shale, the
<br />coal bearing Mesa Verde Group, and the Lewis shale. The Mancos and Lewis shales
<br />are of marine origin and the sediments of the Mesa Verde Group are of transitional
<br />to non-marine origin. The Menefee formation, the middle member of the Mesa Verde
<br />Group, is the primary coal bearing formation.
<br />MANGOS SHALE
<br />The Mancos shale conformably overlies the Dakota sandstone and is
<br />approximately 2,000 feet thick. It consists of dark gray to black shale and silty to
<br />fine sandy shale with small amounts of dark-gray argillaceous limestone in lenses
<br />and concretions which weather to a bright yellow brown color.
<br />POINT LOOKOUT SANDSTONE
<br />The Point Lookout sandstone is the basal formation of the Mesa Verde Group
<br />in the Hesperus area. In this report, the Point Lookout sandstone is divided into two
<br />members: a lower member made up of thin sandstone beds with inter-bedded shale
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<br />National King Coal, LLC King I Mine
<br />Section 2.04.6
<br />Page 1 February, 2007
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