The Underpinnings
San Antonio lies at the junction between the two great land forms of the western United States: the Great Plains to the west and the Coastal Plains to the east.
In Texas, the boundary between these regions is a zone of considerable geologic faulting and relative displacement of the earth’s crust. Perhaps the most dramatic expression of this displacement occurs along the Balcones Escarpment below which most of San Antonio is situated.
The rugged, highly dissected edge of the escarpment is is a transition zone known as the Balcones Canyonlands. The land to its west is known as the Edwards Plateau; the land to its east is known as the Gulf Coastal Plain.