Annual report for the Bureau of Economic Geology 1972
A thick sequence of Lower Cretaceous limestone and dolomite, known traditionally and informally as Edwards," covers much of west-central Texas and composes one of the dominant physiographic elements of the State, the Edwards Plateau. In this region the base of the Edwards is an important fresh-water aquifer. Along the inner edge of the Gulf Coastal Plain, in the Balcones fault zone, the Edwards is also exposed but severely faulted and altered by ground water. South and east of the Balcones fault zone these same rocks dip gently gulfward beneath the coastal plain.
Mountain-bounded basins or bolsons are the most important aquifer systems throughout most of southwestern and western United States and northern Mexico. The dissection of the Presidio Bolson by the Rio Grande and its tributaries has afforded an ideal situation for detailed study of the stratigraphy of one of these important aquifer systems. The results of this investigation provide a framework for understanding the relationships between the types and distribution of bolson-fill sediments and the occurrence of ground water in desert basins in the United States and Mexico.