At the time when the Dene moved south at 800-1200 AD, their
poorly made asymmetric arrowheads were mainly side and corner-notched,
some like Prairie Side-Notched. The Dene met with Plains Indians
as the Aspen Parkland and Boreal Forest interface moved north with
climate warming before the Little Ice Age. After entering the Northern
Plains, the Dene adopted the Plains Side-Notched pattern.