In this slide we see the igneous rocks that intruded the edge of North America exposed by the late Paleozoic truncation fault. These granites are ~252ma and are overlain along an unconformable contact by conglomerates composed of the same granitic materials. This granite suggests that the edge of south-western North America were subject to subduction following truncation and formed the beginnings of a Continental Andean arc sometime before 252ma. Image courtesy of Professor Burchfiel.