Additional Quaternary uplift of southern Canadian rockies. Glacial carving from Pleistocene ices sheets gives everything it's present shape. Mediterranean like climate and everglades. Eustatic sea level rises 250 meters. Seaway swells and shrinks repeatedly but separates North America into two for 35 million years.
Seas drain out.
Forest recedes and becomes grassland. Braided rivers flow North-South and deposit across plains. At 700,000 ice doubles in size and starts following closer to the 100,000-year eccentricity cycle. Keewatin ice sheet meets Cordilleran sheet at Rockies and Labrador sheet through Manitoba. Deglaciation is fast, starting at 18,000, in two or three stages, with the addition of numerous unstable ice lobe fluctuations, which increase as the ice thins.