LAKE-LEVEL FLUCTUATIONS AT THE END OF THE PLEISTOCENE IN THE LAHONTAN BASIN, NEVADA, AS A CONTROL ON THE DISTRIBUTION OF PALEOINDIAN SITES

When humans first entered the Great Basin between about 11,500 and 11,000 yr B.P., pluvial lakes in the region had already retreated from their late Pleistocene highstands and were probably at relatively low levels. Soon thereafter some of the lakes rose to moderately high levels, causing a dramatic expansion of wetland resources. This presentation focuses on the spatio-temporal relationships between lake-level fluctuations and the distribution of Paleoindian sites in the Lahontan basin.

Near the Pleistocene-Holocene transition (PHT), coalescing lakes in the western subbasins of Lahontan reached an elevation of about 1230 m while a separate lake in the Carson Sink reached an elevation of about 1235 m. Although the 1230 m shoreline in the western subbasins remains undated, a stratigraphically and geomorphically related beach ridge at 1212 m yielded an age of 10,820 +/- 35 yr B.P. (Briggs et al., 2005). In the Carson Sink, Caskey et al. (2004) reported two ages of 9950 +/- 60 and 8060 +/- 70 yr B.P. from sediment beneath a beach ridge at 1228 m. Based on the morphology and sedimentology of beach ridges associated with these lake-level rises, fluctuations in water level were rapid and little time was spent at any given level. Therefore, Paleoindian sites should not be expected to be associated with only the highest of these shorelines, but instead are probably associated with a range of shoreline elevations.

The distribution of Paleoindian sites in the Lahontan basin is in general agreement with the lake-level records. No cultural dates from the PHT have been generated from caves or rock shelters below 1220 m in the Lahontan basin. In a survey of all beach ridges between 1230 and 1185 m at the north end of Winnemucca Lake, the Coleman locality on the 1218 m shoreline is the only Paleoindian site. Similarly, the extensive Sadmat site in the Carson Sink is distributed along beach ridges at about 1235 m.

In summary, Paleoindian sites are not found on the floors of the western subbasins and the Carson Sink, but instead are commonly found along shorelines at moderately high levels that date to near the PHT or in caves and rock shelters at or above these shorelines. This spatio-temporal relationship suggests that people were utilizing wetland resources associated with these greatly expanded lakes shortly after they first arrived in the Great Basin.