Hydrostratigraphy, hydrodynamics, and hydrochemistry--Geologic controls of ground-water phenomena in the San Juan Basin
— William J. Stone

The San Juan Basin is a Laramide depression containing approximately 15,000 ft of sedimentary deposits. This general geologic framework, a thick and varied stratigraphic section together with a basin structure, exerts a strong infl uence on the occurrence, movement, and quality of ground water in the region. The depositional history of the region produced limestone, sandstone and alluvium aquifers separated by mudrock aquitards. This complex stratigraphic sequence and the basin structure result in confi ned hydraulic conditions. Hydrodynamically, the basin has evolved through the compaction (discharge) stage to the equilibrium (recharge) stage. Recharge occurs where aquifers crop out or subcrop beneath alluvium and colluvium. The rate of recharge varies with aquifer type and landscape setting. Flow direction is generally basinward, controlled by dip. Rates of movement are greatest in the permeable sandstones and limestone. Discharge areas are associated with topographic lows, principally stream valleys. Total-dissolved-solids content of water in the sandstone aquifers varies with associated rock type, grain size of the water-bearing unit, and distance from recharge areas.