Surface strata of the North-Central Plains (Pl. 9) are westward-dipping
Pennsylvanian, Permian, and Triassic rocks. Present also are extensive
exposures of Quaternary sands and gravels which trend north-south across
the central portion of the region. The area is bounded on the west by
the High Plains, on the east by the Grand Prairie, and on the south by
the Edwards Plateau and Llano uplift. Many vertebrate fossils have been
collected from the Permian and Triassic rocks of this area. There are
also many excellent outcrops of fossiliferous Pennsylvanian formations
in the North-Central Plains region.