Missed this one the first time around : an
excellent article on how it is that Paleo lithic technology and subsistence strategies could have persisted on the plains and points south when pretty much "everything" (climate, landscape, flora/fauna and -- probably -- people) changed elsewhere, ushering in the "Archaic" era.
Apr. 12, 2010 : "The joint team carried out an extensive review of climatic and environmental records spanning the Younger Dryas period, looking carefully at all pieces of climate evidence that might have affected Northern America. Important regions such as the Great Plains and the Rocky Mountains were found to have suffered very little at the hands of the dry spell, which means that groups living here might have felt no difference in overall conditions during the entire length of the geological period. Details of the new investigation appear in the latest issue the Journal of World Prehistory."
Early Paleoindian Groups Unaffected by Younger Dryas - Softpedia