Lithology and Stratigraphy. Cretaceous period with Paleocene and Eocene period sedimentary rocks occur, which are dominantly shales, sandstones, and siltstones. The Book Cliffs are carved mainly from marine Cretaceous sandstone, the Roan Cliffs of Paleocene and Eocene epoch river and flood plain deposits, and the Badland Cliffs are from Eocene epoch lakebeds. Entisols and Aridisols occur in combination with mesic and frigid soil temperature regimes, along with aridic soil moisture regimes occur at the lowest elevations. Inceptisols are common with Douglas-fir.
Most soils have concentrations of calcium.
Potential Natural Vegetation. Historically, desert bighorn sheep were found in the area, but were extirpated with the advent of settlers and widespread livestock grazing. Though moose probably are not indigenous, their range is now expanding into suitable habitat. Mountain bighorn sheep have been introduced in localized areas. Ring-necked pheasants, also introduced, are becoming more abundant.