We now consider the time between the middle Jurassic (Jr) and the late Cretaceous (K). In this image you can see the red magmatic arc mountain belt extending up the entire western edge of NA. Within the U.S., the sequence of geologic environments is relatively consistent along this margin. From west to east, the regions are: Accretionary Prism / Fore Arc / Arc Intrusions / Metamorphic zones related to the intrusions / back arc fold and thrust belt / Fore-Deep Basin. The eastern extent of this fold and thrust belt is shown by the outline labeled as Sevier Belt. The grey-brown coloring indicates the location of the fore-deep east of the fold and thrust belt. Note that this deformational and depositional style does not extend south to the Mojave region. The situation in Canada is different—arc collisions continue into the Cretaceous and the subduction zone and its associated magmatic arc migrate to the west. Courtesy of Prof. Burchfiel.