 Identifiable from the mid @-@ Miocene period , it has recorded changes in the western @-@ moving North American Plate because it is believed to have been relatively stationary for tens of millions of years . Since then it has formed a line of volcanoes called the Anahim Volcanic Belt , stretching from the coast to the Interior Plateau near Quesnel . Each of the volcanoes was once over the hotspot , but migration of the North American Plate has pulled the volcanoes away from the hotspot 's magmatic source at a rate of 2 cm ( 0 @.@ 8 in ) to 3 @.@ 3 cm ( 1 @.@ 3 in ) per year . As a result , the volcanoes are progressively older to the west . The composition of magma to the volcanoes and its supply change with time as the volcanoes grow over the hotspot and migrate away . 
