The Nature and Age of the Contact between the Laurentide and Cordilleran Ice Sheets in the Western Interior of North America

Abstract

The presumed existence of a single mass of coalesced Cordilleran and Laurentide ice during most of late Wisconsin time is central to many archaeological hypotheses on the peopling of the New World. The area under concern is a 2,400-km belt of the Western Interior Plains and adjacent mountains, extending from the 49th parallel to the Arctic Ocean. Multiple Cordilleran glaciation occurred in the Rocky Mountain area during both late and early Wisconsin time. Radiocarbon dates indicate the mountain valleys were largely ice-free by 10,500 BP. Multiple Laurentide glaciation also is well established, the last advances in southern Alberta (late Wisconsin) having terminated east of the mountain front. Southern Alberta and southwestern Saskatchewan were ice-free by ca. 15,000 BP. Incontravertible evidence for coalescence west of the late Wisconsin ice front comes only from the Athabasca Valley, where Roed found that the two glaciers coalesced and flowed southeast. This event occurred either in early Wisconsin or Illinoian time. Since then the western border of the plains of Alberta has remained ice-free.