Sediments of the Fredericksburg Division in south-central Texas were deposited on the slowly subsiding west flank of the Tyler basin. In this region there are three stratigraphically distinct areas. The southern area has a thick Edwards Limestone unit overlying a thin Walnut Formation.
The red upper unit of the Hickory Sandstone is a hematitic and goethitic sandstone containing a large reserve of potential low-grade iron ore. It is estimated that about 7 million long tons of elemental iron is locked up in each square mile of the upper 30 feet of this deposit in sandstone averaging about 12.4 percent elemental iron.
The Red River rises in northeastern New Mexico and extends across northern Texas and east of the Panhandle serves as the northern border of that State. The late Cenozoic geology of the Red River basin has been studied intensively in northwestern Texas and in Louisiana.