In the northern Canadian Cordillera three major Proterozoic assemblages show a distinct sinistral separation along the long-lived Richardson-Hess fault zone. It is suggested that this separation resulted from displacements along a mid-Paleozoic sinistral fault system connecting the Devonian-Mississippian Ellesmerian orogen of the Arctic with the Antler orogen of the western United States. Composite displacement of possibly hundreds of kilometres along this fault system created transpressional and transtensional deformation along the western outer margin of the North American craton. Deformation was accompanied by eastward progradation of turbiditic chert-quartz arenites, local igneous activity, and exhalative ore deposition. Extensive late Mesozoic and Cenozoic compression and extension probably greatly modified mid-Paleozoic fault-related deformation patterns.