As the focus of their hunting activities disappeared, the Paleoindians had to change their way of life to survive. No longer would they be so nomadic and no longer could they seek the big game animals. They began to settle in to more local environments such as in a large river drainage system. They tended to use more resources from the environment rather than just a few. The kinds of artifacts they made were more varied and included objects such as ground stone axes.
Archaeological evidence shows more use of plants.
These were people of the Archaic period, as archaeologists call it. Evidence of Native American Occupation in Nebraska The Heritage of the Nebraska Sand Hills web site has a brief discussion of the transition from Paleoindian to Archaic. This page from the Iowa OSA discusses what happened as the glaciers went away, the mammoths disappeared and the cultures changed. The whole transition is documented fairly well from central Texas. The cultures of the Archaic period throughout the Plains became very well adapted to the changes in the climate.