Burchett, R. R., 1979. The Mississippian and Pennsylvanian (Carboniferous) Systems in the United States-Nebraska (GSI-5) 15 pp., size 8.5" x 11". Description Nebraska is underlain by rocks of Mississippian and Pennsylvanian age in all but the northeastern corner of the state. However, only some of the Upper Pennsylvanian strata are exposed, and the outcrops of these rocks are restricted to valley sides in the southeastern part of the state. For this reason, the description of Carboniferous rocks in Nebraska is limited almost entirely to those deposited during Late Pennsylvanian time.