From abstract: Siliciclastic and minor carbonate rocks of the lower part of the Middle Pennsylvanian Minturn Formation of north-central Colorado were deposited in alluvial-fan, braidplain, Gilbert-delta, shoreline, and paralic, and offshore-marine environments. These strata can be divided into twelve genetic sequences that are generally bounded by transgressive surfaces of erosion or paralic flooding surfaces, and are characterized by thin and thick transgressive units. This report examines the paleogeography of this area.