HYDROGEOLOGY OF THE SACRAMENTO MOUNTAINS IN SOUTHEASTERN NEW MEXICO: HOW KARST CREATES AN OASIS IN THE DESERT

Karst features in dryland regions can have profound effects on the hydrogeology, including groundwater recharge, movement, and water quality. In areas with higher potential evaporation than precipitation, recharge, and the down-gradient availability of water depends largely on water quickly bypassing the root zone. Karstic dissolution features provide this fast path for infiltration, and subsequent groundwater flow. Therefore, karst may enhance recharge in even semi-arid mountains and out into the regional aquifer.

The Sacramento Mountains are located in southeastern New Mexico and serve as a recharge area for adjacent regional aquifers, which underlie regions that are characterized by arid to semi-arid climates. These mountains, with peaks up to 3,000 meters ASL, slope gently to the east towards the Pecos Valley. Hundreds of springs are located throughout these mountains. This relative abundance of water creates a lush mountain setting with mixed conifer forests and abundant wildlife. Much of this water ultimately makes its way into the Roswell Artesian Basin (RAB) regional aquifer, which supplies water for one of the most intensively farmed areas in the state.

The Permian San Andres Limestone caps the ridges and lies above the Yeso Formation which is composed of interbedded carbonates, shale, siltstone, and sandstone. Dissolution of carbonates and originally abundant gypsum has created “sandwich” karst with chaotic bedding, collapse features, and dissolution breccias. Groundwater flow mainly occurs in the carbonate layers in the Yeso. The extreme heterogeneity of the Yeso Formation results in hundreds of springs at multiple elevations. Water chemistry in springs and groundwater evolves from a Ca-HCO₃ water type at high elevations to a Ca-Mg-SO₄-HCO₃ water type at lower elevations due to dedolomitization. Stable isotope data for springs and wells show higher degrees of evaporation at lower elevations. These data indicate that recharge, which was estimated to be approximately 21% of average annual precipitation, primarily occurs above the elevation of 2,380 meters. Groundwater flows down gradient via a series of perched karstic aquifers that are connected by fractures and mountain streams. Groundwater in the Yeso continues flowing to the east to recharge the RAB aquifer.