PRELIMINARY PALEOLIMNOLOGIC DATA FOR THE WALKER \u27LAKE SUBBASIN, CALIFORNIA AND NEVADA

In order to understand the chemical evolution of Walker Lake and past changes in the Walker River hydrologic system, the Walker Lake subbasin in California and Nevada has been the site of gravity, piston, and rotary wireline coring activities since 1975. Chemical and physical measurements made on sediments and pore fluids from these cores indicate that Walker Lake has undergone significant changes in size over the past 360,000 years. From 360,000 to 130,000 years before present (1950), Walker Lake frequently was shallow or dry. From about 130,000 to 21,000 years before present, the water level in Walker Lake was at moderate or high levels. From about 21,000 to 15,000 years before present, Walker Lake was extremely shallow and probably desiccated numerous times. Sediments representing the last Lake Lahontan highstand, that occurred between 14,000 and 12,500 years before present, were not recovered during offshore coring. For the past 10,000 years, the water level in Walker Lake has been at moderate to low levels and probably desiccated twice since the end of the last highstand that occurred 12,500 years before present; that is, those desiccations occurred greater than or equal to 4,700 years before present and again 2,600 years before present. Desiccations of Walker Lake can be attributed to changes in climate or diversion of the Walker River into the Carson River drainage (Benson and Thompson, 1987a). Seismic-reflection data indicate subsidence along both the east and west shores of Walker Lake. Tectonic activity responsible for the subsidence appears to have stopped between 9,000 and 7,000 years before present