It extends east to the Mid-Atlantic Ridge and west to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust. The interior of the landmass is an extensive granitic craton. Along most of the edges of this craton are fragments of crustal material called terranes. They are stuck on (accreted) to the craton over a long span of time. Much of North America west of the Rocky Mountains is composed of such terranes.