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i formation is characterized by irregular 'bedding and rapid lateral changes in lithology. The contact of the Menefee with the underlying Point Lookout Sandstone is conformable. In most places, the contact is marked by a sharp break between the carbonaceous shales and coals of the Menefee and the clean sandstone of the massive member of the Point Lookout. Locally, through the Eastern half of Township 35 North, Range ]2 West, the basal Menefee is reported to consist of massive sandstones and the separation is not really made. The Menefee Formation thins in an Eastward direction from approxi- mately 350 feet in the Cherry Creek Valley, about four miles West of the Hesperus project area, to about 723 feet in the Florida River Valley about 15 miles East of the project area. i li Most of the variations of thickness of the Menefee Formation are reported to be thinner where the more compressible shale and coal dominate the • section. Locally, thickness variations of the Menefee can be attributed to scouring action of the water source responsible for the disposition of the overlying Cliff House Sandstone. From an area near the head of Hay Gulch in Section 27, Township 35 North, Range 7] West, cast to the La Plata River, the upper coal bearing horizon is significantly thinned and apparently replaced by the overlying Cliff House sandstone. This upper coal bearing horizon is scoured to where the upper coal seam, so prevalent in the Hay Gulch area, is completely absent. The Menefee Formation is of nonmarinc origin throughout the Hesperus area. The petrology of the formation varies with its lithologic character, but over most of the area it is slightly less resistant that the overlying and underlying formations. Cliff House Sandstone: The Cliff (louse Sandstone is the upper forma- tion of the Mesa Verde Group in the Hesperus area and is of marine origin. It generally consists of irregular to lenticular lenses of hard fine to medium • grained calcareous sandstone interbedded with softer, fine grained, ar9illa- ceous sandstone, mudstone and silty shale.