since the sevier and laramide orogenies occurred at similar times and places, they are sometimes confused. in general the sevier orogeny defines a 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.