Paleontology and geology
Although no rocks of Carboniferous age are shown on this map, exposures of these rocks do occur in the Bighorn and Owl Creek Mountains in the north-central part of the state, as well as in the Black Hills in northeastern Wyoming. Early Carboniferous (Mississippian) rocks are mainly limestones, originally deposited as limy sediments on the floor of a shallow sea. Fossils of trilobites, brachiopods, corals, crinoids, and other marine organisms are common in these rocks.
Late Carboniferous (Pennsylvanian) rocks record the retreat of the sea from Wyoming. Nearshore sandstones, limestones, and shales were deposited at this time, and evaporites and dolostones occur in some places.