The main tectonic events of Balcones faulting are generally thought to have occurred during the Miocene, but there is considerable evidence that periodic structural adjustments also took place in the Cretaceous. For example, mafic alkalic volcanic plugs of Late Cretaceous age occur at the surface and in the subsurface all along the Balcones fault zone. The geochemistry and petrology of these igneous rocks suggest that they penetrated the entire crust of the Earth. Dramatic changes in the landscape occur across this crustal discontinuity. On the west are plateau uplands and ruggedly dissected limestone hills.
Soils are thin and stony, and the main agricultural use of the land is for range.
The dominant native vegetation assemblage is juniper-live oak savannah, and groundwater is generally of good quality with ample quantities occurring at shallow depths from limestone aquifers. On the east side of the escarpment, terrain consists of rolling prairies and broad river bottoms. Soils are thick fertile clays, which compose prime arable land. Native prairie grasses were dominant before the agricultural activities supplanted them, and groundwater in large amounts is available only at considerable depth and is commonly tepid and brackish. The escarpment is also a major weather-maker.