Hydrostratigraphy and allostratigraphy of the Cenozoic alluvium in the northwestern part of Las Vegas Valley, Clark County, Nevada

David Joseph Donovan, University of Nevada, Las Vegas


This investigation was conducted to determine the location, nature, and boundaries of the most permeable unit within the alluvial aquifer material in Las Vegas Valley. It was prompted by declines in specific capacity of about 90% at the Las Vegas Valley Water District's West Central Well Field. It was hypothesized that the decline in specific capacity resulted from dewatering of the most permeable interval of the alluvium. Lithologic descriptions from wells and aquifer test information were analyzed for geologic and hydrogeologic variability. New information, in the form of detailed unpublished lithologic and hydrologic information, was available from twenty water wells drilled between 1989 and 1994; The geology was defined using allostratigraphic units; Aquifer test and lithologic information was used to define the boundaries of units of differing permeability within the subsurface. These units of differing permeability are the six (6) hydrostratigraphic units introduced in this investigation. The most permeable hydrostratigraphic unit is a distinct 20 to 90 m thick horizon, lying generally above 230 m below land surface. When the production wells were first installed at the West Central Well Field in the 1960's, most of the permeable unit was saturated. In 1993 the potentiometric surface was at or below the bottom of this hydrostratigraphic unit. (Abstract shortened by UMI.).