Historical potentiometric surface of the Edwards-Trinity aquifer system and contiguous hydraulically connected units, west-central Texas

The Edwards-Trinity aquifer system is a sequence of near-surface, hydraulically connected, Cretaceous carbonate and quartzose clastic rocks that underlie about 42,000 mi² of west-central Texas (fig. 1). The aquifer system is currently (1991) being studied as a part of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) program, which is intended to describe the regional hydrogeology of important aquifer systems nationwide.

The purpose of this report is to present a potentiometric-surface map of the principal aquifers of the Edwards-Trinity aquifer system based on the earliest available data; to explain in general terms what the potentiometric surface represents relative to rainfall conditions and ground-water withdrawals; and to discuss the major factors that control the configuration of the potentiometric surface.