at its maximum extent continental glacial ice in north america extended as far south as
Last Glacial Maximum In North America, the ice covered essentially all of Canada and extended roughly to the Missouri and Ohio Rivers, and eastward to Manhattan. In addition to the large Cordilleran Ice Sheet in Canada and Montana, alpine glaciers advanced and (in some locations) ice caps covered much of the Rocky Mountains further south. Latitudinal gradients were so sharp that permafrost did not reach far south of the ice sheets except at high elevations. Glaciers forced the early human populations who had originally migrated from northeast Siberia into refugia, reshaping their genetic variation by mutation and drift. This phenomenon established the older haplogroups found among Native Americans, and later migrations are responsible for northern North American haplogroups.[15]