Three additional events are important during Mississippian-Permian time in western North America: the formation of the ancestral Rockies east of the Cordilleran belt, the formation of the Havallah Basin and the strike-slip formation of the southwest continental margin. This latter event set the stage for Mesozoic subduction beneath the continental crust in the southwest Cordillera. The Havallah sediments, deposited in a distal marine basin, were a lot like the Antler sediments before they were thrust over the western edge of North America. In the Permian, these marine sediments were thrust up and over the western edge of North America, overlapping the rocks of the Antler Orogeny. No oceanic crust in found in either the rock of the Antler or the Havallah Orogenies. The sediments could have been scraped off a down-going plate like in Accretionary wedges. The difference between the two events is that the accretion of the Havallah basin sediments was driven by an Island Arc collision. The island arc emplaced west of the Havallah sediments had an accretionary wedge on its western edge that contains marine sediments that range in age between Cambrian and Permian. These accretionary wedge sediments contain a fossil assemblage that is not of North American but rather of Asian affinity. This fossil evidence suggests that during arc formation vast areas of oceanic crust were subducted beneath the west side of the arc, some coming from the Asiatic side of the PaleoPacific. We know that the Havallah basin was close to North America as its fossils are of North American affinity. Some workers debate whether the Havallah basin did not directly collide with North America, but rather was transported laterally into position along large transverse faults like those found on the South Island of New Zealand today. An onlap sequence of sediments of Triassic age cover the Havallah and Antler rocks, demonstrating that the mountains created by these accretionary events were eroded away and subdued enough to have shallow marine rocks deposited over them. Image courtesy of Professor Burchfiel.