Abstract: A Geophysical Study of Subsurface Damming at Little Lake, California

THOMPSETT, BRETT S., SCOTT SALBERG, ROB NEGRINI, and JAN GILLESPIE

Little Lake and the five adjacent ponds are important contributors to the groundwater in the Indian Wells Valley, CA, The chemistry of the groundwater found in wells south of the area strongly support significant quantities of water moving through the Little Lake area (Austin, et al., 1996). The northern ponds gain hydrologically while the southern ponds are losing (Gillespie, 1995). It is postulated that a basement high located immediately south of the gaining ponds is acting as a subsurface dam. In this study we test the above hypothesis using 2D gravity and magnetic surveys. Survey stations were established along a 4.3 km. survey line trending approximately parallel to the groundwater flow.

A gravity anomaly of +1 mgal was observed at the location of the postulated subsurface basement high. Gravity modeling showed that a 0.2 km high in the granitic basement can produce the observed gravity anomaly. A +50 gamma magnetic anomaly, which has the same wavelength as the gravity anomaly, was observed in the same location. This anomaly further supports the existence of the hypothesized subsurface basement high.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California