The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south. The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred from approximately 160 million years (Ma) ago to around 50 Ma. This orogeny was caused by the subduction of the oceanic Farallon Plate underneath the continental North American Plate. Crustal thickening that led to mountain building was caused by a combination of compressive forces and conductive heating initiated by subduction, which led to deformation. The Sevier River area of central Utah is the namesake of this event. Extent The Sevier Fold and Thrust Belt extends from southern California near the Mexican border to Canada. Basin and Range faults cut the older Sevier thrust faults. The Sevier orogeny was preceded by several other mountain-building events including the Nevadan orogeny, the Sonoman orogeny, and the Antler orogeny, and partially overlapped in time and space with the Laramide orogeny. Sevier or Laramide? Early Sevier thrusting began well before initial Laramide deformation. However, there is evidence that suggests late Sevier faults were active during the early Laramide. The majority of Sevier deformation occurred west of Laramide deformation, but there is some geographic overlap between the eastern Sevier margin and the western Laramide margin. In southwestern Utah, Sevier thrusts may have remained active until the Eocene, while Laramide deformation began in the Late Cretaceous. Since the Sevier and Laramide orogenies occurred at similar times and places, they are sometimes confused. In general the Sevier orogeny defines an older, more western compressional event that took advantage of weak bedding planes in overlying Paleozoic and Mesozoic sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “thin-skinned” thrust faults that generally get younger to the east. In contrast, the Laramide orogeny produced “basement-cored” uplifts that often took advantage of pre-existing faults that formed during rifting in the late Precambrian during the breakup of the supercontinent Rodinia or during the Ancestral Rocky Mountains orogeny. Geologic structures The Sevier orogenic belt consisted of a series of thin plates along gently dipping west thrust sheets and moving from west to east. These thin skinned thrusts moved late Precambrian to Mesozoic age rock of the Cordilleran passive margin east. The Sevier meets the Laramide orogenic belt on its eastern side. The Sevier and Laramide combination is similar