The Blackland Prairies consisted of about 11,500,000 acres, including the San Antonio and Fayette Prairies. Topography of the Blackland Prairies region is gently rolling to nearly level and well dissected for rapid surface drainage. Elevation varies from 300 to 800 feet above sea level. Average annual rainfall ranges from 30 to 40 inches increasing from west to east. May is the peak rainfall month for the northern end of the region; however, the south-central part has a fairly uniform distribution throughout the year.
Fairly uniform dark-colored alkaline clays, often referred to as “black gumbo,” interspersed with some gray acid sandy loams, characterize the area.
The Blackland Prairies was true tallgrass prairie with little bluestem as a climax dominant. Other important grasses were big bluestem, Indiangrass, switchgrass, sideoats grama, hairy grama (Bouteloua hirsuta), tall dropseed (Sporobolus asper), silver bluestem and Texas winter-grass. Under heavy grazing, Texas wintergrass, buffalo grass, Texas grama (Bouteloua rigidiseta), and many annuals increase or invade. Mesquite also has invaded hardland sites of the southern portion of the Blackland Prairies. Post oak and blackjack oak have increased on the medium- to light -textured soils.
According to the Texas Parks and Wildlife Department, 99.9% of the Blackland Prairie is lost to other land uses. Only a few remnants are protected as hay meadows or conservancy land.
Isolates of the Blackland Prairies occur in the Oak Woods and Prairies region. These areas may be identified by their characteristically dark clay soils.