Late Wisconsin groundwater discharge environments of the southwestern Indian Springs Valley, southern Nevada

Badland exposures in the Indian Springs Valley, southern Nevada, contain evidence of formerly widespread spring and seep discharge. The stratigraphic position and appearance of most of these deposits suggests correlation with late Wisconsin (30,000 to ca. 10,000 yr B.P.) marsh sediments in nearby Las Vegas Valley. Previously, all these deposits have been loosely described as lacustrine because of the presence of extensive green mudstones associated with aquatic mollusks. However, this association also typifies modern groundwater discharge environments in many basins of northeast Nevada such as the Steptoe Valley, basins often without hydrographic closure. Such analogs best explain the origin of late Wisconsin fine-grained deposits in the unclosed southwestern arm of the Indian Springs Valley. Key features of these depositional systems are the lack of shoreline deposits, the presence of a broad belt of subaerially deposited plae-brown silts surrounding spring, "wet meadow," and marsh deposits, and the intermixture of terrestrial and aquatic mollusks in most horizons where mollusks occur.