According to Mackenzie the Beaver occupied the entire basin of the Peace River below its junction with the Smoky, the area around Lake Claire and the valley of the Athabasca as far south as the Methye Portage. The “Slaves” he mentions are possibly those assumed by Diamond Jenness to have lived around Lesser Slave Lake (and may be the Beavers who were described to Goddard in 1914 as extinct “A long time ago”.)
Before 1760, bands of Cree invading along the “Old Cree War Trail” from west of Edmonton and bearing guns obtained from the fur traders, wiped out the “Slaves” around Lesser Slave Lake, and penetrated the Peace-Mackenzie watershed driving the Beaver back into the basin of the Peace. The Beaver, in turn, pushed the Sekani into the Rocky Mountain Trench where they have more or less remained to this day.