The Blackland Prairie land resource area encompasses approximately 960 square miles within the Basin and comprises the entire area upstream of Iron Bridge Dam and the extreme upper portion of the Lake Fork Creek subwatershed. The soils of the Blackland Prairie are primarily of the Houston Black, Houston and Austin series, with smaller areas of Bell, Lewisville, Sumter and Eddy soils. The Austin and Eddy soils are dark grayish brown to brown calcareous clay soils. The Houston Black and Houston soils are deep dark gray to nearly black calcareous clays which are sticky and plastic when wet. Sumter soils are yellowish brown clays, and Bell Lewisville soils are deep dark gray to brown calcareous clays on stream terraces.
Native vegetation consists of bunch and short grasses with hardwood trees in the stream bottomlands.
The Blackland Prairie soils are among the most productive upland soils in the State. However, because of the clay texture and sloping surfaces, they are very susceptible to erosion. The East Texas Timberlands area comprises about 88 percent of the Basin. The soils are mostly light- colored fine sandy loams with subsoils that range from loamy sand to plastic clay in texture and from yellow to red in color. The soils are low to very low in the essential plant nutrients but are very responsive if properly fertilized.