HOLOCENE CLIMATE CHANGES AND WATER SUPPLY FOR NATIVE AMERICANS ON THE SOUTHERN HIGH PLAINS, USA

What was the source of water used by Native Americans occupying the riverless, semi-arid Southern High Plains (SHP) of Texas and New Mexico, USA, during periods of aridity in the Holocene? It is known that springs in draws (presently dry river valleys) provided some water; but they have limited distribution and would have ceased to flow and filled with eolian sediment during periods of aridity, thus exacerbating the extraction of water. It is proposed that the fresh-water springs in the widely distributed 40 to 50 large saline-lake basins in the southwestern half of the SHP could have provided continuous water during Younger Dryas, Altithermal, and sand-sheet periods of aridity. The dynamic equilibrium between the floor of the basins and ground-water levels would have maintained a constant ground-water gradient to the lake basins even under conditions of a declining water table. This gradient ensured continuous spring discharge, although the mouth of the spring declined in elevation. To establish the validity of the dynamic equilibrium concept in large saline-lake systems, it was necessary to show that sediment accumulated as lunettes adjacent to the lakes during periods of known aridity, when the water table would have declined. Data from a 17.7-m core from the inner lunette at Double Lakes, Texas, provided twelve optical stimulated luminescence dates that cluster around 11.5, 6.6, and 4.9 ka. These dates correspond respectively to the Younger Dryas, Altithermal, and sand-sheet periods of Holocene aridity known to exist from other evidence and confirm the dynamic equilibrium of the system. Thus, springs in these basins could have provided a continuous source of potable water to Native Americans during periods of extended aridity. Additionally, these springs may have attracted large, highly valued herbivores (bison, antelope, and deer) and smaller animals, making hunting near them more productive.