Uppermost Cretaceous and Lower Tertiary rocks total about 3,000 ft (g15 m) in thickness in the Denver basin. Sandstone, shale, and coal of the Upper Cretaceous Laramie Formation are unconformably overlain by conglomerate and sandstone of the Upper Cretaceous Arapahoe Formation overlying Denver Formation, which includes the Cretaeous-Paileocene boundary, is composed of fine-lto coarse-andesitic sedimentary rocks and some coarse arctic beds. It includes inlerbedded carbonaceous shales and lignites throughout most of the basin. A mappable contact separates the Denver from the overlying Dawson Arkose. The lower member of the Dawson, of Isle Paleocene aye, is lenticular and is composed mainly of fine to coarse arkoses with Some aridesilic sedimentary rocks. It may be equivalent to the Green Mountain Conglomerale (Paleocene), which is composed of rocks with similar Lithology. The main body of the Dawson, composed mostly of coarse arkoses and conglomerate, is of Eocene age and overlies a distinctive thick paleosol throughout most of the basin.