The Wisconsinian Ice Age was an epoch when 2 massive Ice Sheets expanded over Canada.  The Cordilleran Ice Sheet expanded over the western Canadian Rocky Mountains south of Alaska, while the Laurentide Glacier covered all of eastern Canada and even extended over New England, Ohio, and other midwestern states.  (Ironically, most of Alaska stayed ice free during this time and consisted of a barren grassy environment known as the mammoth steppe.)  About 30,000 years ago, the Cordilleran Ice Sheet and the Laurentide Ice Sheet conjoined into 1 massive glacial slab that blocked all human and animal migratory routes between Alaska and the rest of America.  Formerly, scientists thought this barrier of ice existed from ~30,000 BP-~11,000 BP, but more recent studies suggest the 2 Ice Sheets began to separate as early as ~15,000 BP, creating an Ice Free Corridor that men and animals could have migrated through.

Map of North America…