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1 REGIONAL GEOLOGY Railhead Industrial Park is situated in the Grand Valley. The valley was formed from the Colorado River's erosion of the Mancos Shale Formation. The Mancos Shale is a black, soft Cretaceous shale which may weather to a light gray or yellowish color. It was formed as a part of a clastic wedge in which sediments were transported eastward from the rising Cordilleran Mountain System. The Mancos Shale may be up to 5000 feet thick. Underlying the Mancos Shale is the Dakota Sandstone, a transgressive deposit at the base of the Upper Cretaceous series. This is a narrow, clean, shoreline deposit which formed between the terrestrial deltaic sandstone and the deeper marine shales. t The most prominent geologic structure in this area is the Uncompahgre Plateau, a broad, gently faulted ~ anticline, one-hundred miles long and twenty-five miles wide. The axis of the anticline trends to the northwest. This formed from regional uplift in the Miocene and Pliocene epochs, when the area was uplifted in the path of the Colorado River. The Colorado River, along with the Gunnison, was diverted ' northward. For a time both rivers flowed through Unaweep Canyon. The Redlands Fault forms on a northern promontory of Uncompahgre Uplift and Colorado National Monument anticline. It slices alongside Pre-Cambrian rock which meets Triassic sandstones in an unconformity, and cuts into the Triassic red beds, and the Wingate and Dakota Sandstone Formations. Adjacent the north side of the Grand Valley, the Mesa Verde group (sandstones with coal lens) forms the prominent Bookcliffs or Palisades, and the lower half of Debeque Canyon. On opposite banks of the Colorado River are shales, siltstones and sandstones of Jurassic age. 1 SOILS AND ALLUVIUM ' Forty-five drill hales, spaced randomly over the expanse of the proposed tract provided information as io the depths of the soil layers and bedrock, and their characteristics. Exposed soils, classified as ' Billings Silty Clay, have been weathered from the Mancos Shale. They are rich in evaporites (salts and gypsums) and sulphates, and generally have low organic content and slow to very slow permeability rates. These soils will be caustic to any concrete structures which may be incorporated. This overburden clay material is underlain by alluvium deposited by the Colorado River. The alluvium is Quaternary in age. It probably consists of granular materials, large cobbles and gravel with rich ' 2