Strata are Tertiary marine sediments consisting of glauconitic, calcarious, fossiliferous strata with lignitic sandy and argillaceous deposits. Soils are mostly Ustalfs. Paleustalfs and Albaqualfs are on uplands and other areas with thick sandy surface. Pelluderts, Pellusterts, and Hapludolls are on flood plains and clayey terraces along major rivers. These soils have a thermic temperature regime, an ustic moisture regime, and montmorillonitic mineralogy.
Soils are deep, medium textured, and generally have a slowly permeable, clayey subsoil.
Moisture may be limiting for plant growth during parts of the year. Potential Natural Vegetation. The oak-hickory cover type consists of scarlet, post, and blackjack oaks, and pignut and mockernut hickories. Forests of elm, pecan, and walnut are in bottomlands. Little bluestem is the dominant grass.