Aquifers in the Houston-Galveston area are composed principally of fluvial-deltaic sediments. The Alta Loma Sand is a complexly faulted, high-sand-percent unit that represents a seaward progression of fluvial, delta-plain, and delta-front facies. The Beaumont Formation, overlying the Alta Loma Sand, is a high-mud-percent unit that represents a coastal progression of delta-plain to delta-front facies. Four arbitrarily defined intervals from land surface to 2000 ft indicate superposition of dip-oriented and strike-oriented high-sand-percent trends.
Aquifer geology partly controls short-term and long-term aquifer hydrology. Dip-oriented high-sand-percent trends are optimum locations for ground-water development. Growth faults act as partial hydrologic barriers to ground-water production. Faults between Harris and Galveston Counties have partly isolated the aquifers into two subsystems. In Harris County ground water of low dissolved solids is meteoric in origin, whereas in Galveston County ground water of low dissolved solids is a mixture of meteoric and saline waters.