RECONNAISSANCE BATHYMETRY OF BASINS OCCUPIED BY PLEISTOCENE LAKE LAHONTAN, NEVADA AND CALIFORNIA

The last high lake level (highstand) of Pleistocene Lake Lahontan occurred 14,000 to 12,500 years before present. During that time, Lake Lahontan occupied seven topographic subbasins. In this report, the area and volume of each of these subbasins are given as a function of lake-surface altitude. The present-day altitudes of the seven primary sills that serve to separate the subbasins also are tabulated. These data serve as a basis for continuing studies of the chemical evolution and paleohydrology of closed-basin lakes located in the Great Basin of the western United States. Currently six rivers discharge to the Lahontan basin. The Walker River discharges to Walker Lake, Nevada; the Truckee River discharges to Pyramid Lake, Nevada; the Carson River discharges to the Carson Sink, Nevada; the Humboldt River discharges to the Humboldt Sink, Nevada; the Susan River discharges to Honey Lake, California; and the Quinn River discharges to the Black Rock Desert, Nevada, forming a shallow ephemeral playa. Geomorphic evidence suggests that, at one or more times in the past, the Walker River discharged to the Carson Desert, and the Humboldt River discharged to the Black Rock Desert. Those stream-capture events would have led to creation of lakes in certain subbasins and desiccation of lakes in other subbasins. It follows that change of lake level does not necessarily imply change of climate. During times of major change in the hydrologic balance, lake-level change in each subbasin is a complicated function of river discharge to that basin, and flow in or out of the basin occurring via sill pathways. Only when lake level exceeds 1,308 meters, does Lake Lahontan become a single body of water, that acts in a unified manner to changes in the regional hydrologic balance