New Mexico Geological Society Annual Spring Meeting — Abstracts

We have prepared a map of the regional water table in the southern Sacramento Mountains based on measurements made in water wells in March, 2008 and elevations of flowing springs and gaining reaches of streams. The aquifer system in the southern Sacramentos is developed primarily within the Yeso Formation, a heterogeneous unit composed of siltstone, mudstone, gypsum and fractured limestone. Water-bearing zones are distributed throughout the section. The system is recharged near the crest of the Sacramentos where high mountain springs discharge from small, highly-localized perched aquifers. Streamflow derived from these springs re-enters the groundwater system along losing reaches and may “daylight” multiple times along the flowpath, feeding springs at lower elevations. In most cases it is impossible to determine whether a measured water level corresponds to a perched aquifer or is part of the regional piezometric surface, and the distinction is probably irrelevant at the scale of observation of the entire watershed.

The regional hydraulic gradient is steepest near the crest of the Sacramentos, and progressively decreases to the east. Locally steeper gradients also occur in the vicinity of major faults. More broadly-spaced water level contours at lower elevations in the Sacramentos probably reflect mounding of the water table, in areas where the aquifer is recharged through sinkholes and karst fissures. Because eastward stratigraphic dip is greater than the regional hydraulic gradient, east of the Six-Mile Buckle the aquifer system is developed in karstic limestones of the San Andres Formation rather than the Yeso. The higher transmissivity of the San Andres limestone is reflected in a pronounced flattening of the water table as the southern Sacramentos aquifer merges with the artesian aquifer of the Roswell Artesian Basin.

Water level change maps show that during the period from 2006 to 2007, water levels in the high Sacramentos began rising in response to unusually intense monsoonal rains in fall, 2006. Water levels continued to rise in the subsequent two years, but the center of greatest increase migrated progressively farther to the east, suggesting that the 2006 monsoon event was continuing to be felt as an eastward diffusion of pressure head through the aquifer system.