Date of Award:

1992

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Craig Forster

Abstract

In the Basin and Range Province, the geologic regime of the Pilot Valley, linear trending block faults have isolated many valleys both topographically and hydrologically. Discharge from these arid, closed basins occurs only as evaporation. Minerals dissolved in discharging fluid are precipitated at the valley floor as the liquid evaporates. The resulting salt flats and high density brines are known as playas.

The Pilot Valley Playa surface was sampled concurrently with the recording of a Thematic Mapper remotely sensed image to define the surface conditions that correspond to image data. An association was found between the band 7 (infrared wavelength radiation) image data and the measured depth to water; and between the visible wavelength data and the evaporite mineral deposits on the playa. The specific gravity of the shallow subsurface brine was found to increase as the liquid brine surface approached the elevation of the valley floor. By using the observed relationships, three remotely sensed images were interpreted with respect to temporal changes in the areal extent of playa evaporite deposits and water depth between 1984 and 1988. The visible wavelength data indicated that the areal extent of the evaporite deposits diminished during the study period. The water level at the playa margins was interpreted to have dropped, and at the playa center to have remained stable. These interpretations suggest that a decrease in the extent of evaporite deposition is related to a drop in the water level around the playa margins.

The interpreted changes of the playa surface are used to draw the following conclusions about the hydrology of the Pilot Valley. The distinct variation in depth to water around the playa margin suggests that these areas are influenced by the discharge from the surrounding ranges. The relatively stable water depth in the central playa and the associated thicker evaporite deposits suggest that the subsurface brine acts here as a buffer to discharge variations. If the temporal changes of the playa margins do result from discharge variation, the discharge zone at the base of the Silver Island Range is wider than that of the adjacent, higher elevation Pilot Range.

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