The ice mass that covered most of Canada and parts of the United States, including the Great Lakes area and northern New England, during the Pleistocene Epoch. It originated in northeastern Canada during the Wisconsin Glacial and then spread south and west. At its maximum extent, about 20,000 years ago, it was connected with the Cordilleran ice sheet to the west and covered an area of more than 13,000,000 square km (5,000,000 sq. MI). In some areas its thickness reached 2,400-3,000 m (8,000-10,000 ft). The system began to recede about 14,000 BP.