All of the study area, except for the southwest corner of Frio County which is in the Rio Grande River Basin, lies in the Nueces River Basin. The climate is well suited to agriculture. The growing season is near 280 days and the average temperatures range from 40 degrees Fahrenheit in January to 99 degrees Fahrenheit in July. The study area contains 6,175 square miles of which 4,234 square miles or about 2.7 million acres are suitable for cultivation. Soils are predominately clay loams, sandy loams, and clays.
Slopes are nearly level and gently sloping.
The Edwards and Carrizo Aquifers are artesian aquifers and underly most of the study area. Replenishment or recharge of a confined aquifer occurs wherever the confining bed rises to the land surface. Drilling of a well allows the water to rise above the confining bed. The water surface in the well behaves as if it were that of an unconfined aquifer, only there is no corresponding water surface outside the well casing. The Edwards is a porous rapidly recharged highly permeable limestone aquifer.