Geology
The majority of the South Central Texas Region is underlain by Cretaceous age limestone, which forms the Edwards Plateau. East and south of the Plateau are upper Cretaceous chalk, limestone, dolomite, and clay, with the extensive Balcones Fault Zone system marking the boundary between the Edwards Plateau and the Gulf Coastal Region. The entire sequence dips gently toward the southeast.
A Tertiary age sequence of southeasterly dipping sand, silts, clay, glauconite, volcanic ash, and lignite of the Goliad Formation overlie the Cretaceous age strata. Throughout the region, alluvial sediments of recent age occur along streams and coastal areas. A sequence of clay, sand, caliche, and conglomerate of the Pliocene age Goliad Formation underlie the coastal areas of the region. Overlying the Goliad Formation is the Pleistocene age Lissie Formation, which consists of sand, silt, clay and minor amounts of gravel. The Lissie Formation is overlain by clay, silt, and fine-grained sand of the Pleistocene age Beaumont Formation.
