Geological constraints on hydrology and endangered species habitat at the Desert Studies Center, Zzyzx, CA

ABSTRACT Structural controls regulate and channel groundwater flow to preserve an endangered fish species at the Desert Studies Center in the Mojave National Preserve. A concentrated zone of northwest-southeast striking fractures which aligns through limestone bedrock between the Soda Springs aquifer and MC Spring was mapped and found to be a viable conduit for fluid flow. The fracture zone is characterized by fracture densities up to 6x that of surrounding bedrock, with generally shorter fracture lengths which are more efficient at transmitting water. Zones of karst were also mapped as potential fluid conduits, but found to be discontinuous pods and lenses, which do not transmit significant water at present. Groundwater elevations between the Soda Springs aquifer on the west side of Limestone Hill, and the site of MC Spring on the east side indicate the spring has a hydraulic head of 1.7 m with a local hydraulic gradient that is consistent over 11 months, despite local fluctuations in the water table elevation. In contrast, Iron Spring has variable water levels. Groundwater flow around the limestone inselberg contributes to the inconsistent levels and shifting location, which make Iron Spring a poor long-term habitat for endangered fish species