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.

Geologic map that depicts the surface geology of Rains, Wood, Upshur, Marion, Harrison, Smith, and Gregg Counties and parts of Camp, Cass, Panola, Rusk, Cherokee, Anderson, Henderson, Van Zandt, Hunt, Morris, Franklin, and Hopkins Counties, Texas.

Tropical storms, which cross the Texas coastline with a frequency of 0.67 storms per year, play a major role in nearshore sedimentation on the south Texas coast. Greatest geological effects of these storms are produced by wind-driven waves and by storm surges.

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.