Granitic and volcanic rocks of Devonian age (about 380 million years ago) intrude and are interlayered with the Paleozoic strata of the Omineca Belt. They are probably remains of a volcanic chain (traces of which are found from northern Alaska to California) that formed on the edge of the North American plate, not far from the margin of the continent. We can say this because ash from these volcanic rocks forms layers in Devonian shale in the eastern part of the Foreland Belt in Alberta, near Lac des Arcs on Highway 1, 70 km west of Calgary.