The tectonic origin of the Pennsylvanian–Permian Ancestral Rocky Mountain system is debated. Most models invoke stress from collision along the Ouachita-Marathon belt as the primary driver for Ancestral Rocky Mountain (ARM) (western USA) tectonism, but no existing model has convincingly explained the timing, northeast-southwest contractional kinematics, and amagmatic nature of this system. We propose that stress generated by transpressional deformation along the southwestern (Sonora) margin of Laurentia combined with that from collision along the Ouachita-Marathon and Nevada margins drove uplift and basin development of the ARM. This model explains ARM timing, uplift kinematics, and lack of magmatism, and is supported by a new generation of late Paleozoic global plate reconstructions.

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