Determining Geologic Controls on Major Springs in Death Valley, California Using Geophysical Methods

Springs can be supported by large regional flow systems or relatively small more local systems. The spring will respond differently to local stresses or climatic changes depending on its flow system. It is often difficult to determine the source of a spring due to the remote nature of many springs, and sparse subsurface information. Many springs in the southwestern US are located in remote or environmentally sensitive settings where direct investigations such as drilling are limited or impractical. Geophysical methods can be used in these situations to determine the geologic factors controlling the location of the spring. We conducted gravity, TEM, and resistivity surveys in and around Death Valley National Park to determine the geologic setting for the Texas and Travertine spring line and the Nevares spring mound. The results of the survey provided important details of the subsurface structures around the springs that help define the flow system supporting the spring. Introduction Springs are an important part of many groundwater flow systems and a critical element of desert ecosystems. The location of a spring discharge point is controlled by several geologic factors that form the terminal portion of the flow system. These factors can influence the geochemical signature of the water and determine how the spring will respond to local modifications of the hydrologic regime. Understanding the position of a spring requires information about the stratigraphic and structural conditions beneath the spring. Many springs are located in remote or environmentally sensitive settings where direct investigations such as drilling are limited or impractical. This is particularly true of the desert regions of the southwestern United States. Geochemical methods are often used to fingerprint the source of the spring water. These methods can provide important indirect evidence of the recharge and flow path of a spring, but geologic material along the flow path or near the discharge point can obscure the geochemical fingerprint of the source water making interpretation of the flow path uncertain. This paper discusses how geophysical methods can be used to determine the geologic and structural elements that control the discharge point of a spring. These methods can be used with minimal disruption to the spring and surrounding area and provide a more detailed understanding of the terminal end of a spring’s flow system. Geophysical methods can also be used to direct invasive sampling methods more effectively and with better predictions of the potential impact on the spring.