Cordilleran tectonic trends diverge within the United States to create several distinctive structural provinces. It is proposed that the spreading pattern results from right-lateral distortion of several hundred miles from Paleozoic through modern times across a 300 mile-wide zone from the Colorado Plateau to the Pacific Northwest. Suitable lineaments are indicated on land and sea. Stress-strain patterns within individual structural provinces can be related to this deformation system. The hypothesis is admittedly outrageous and some of its difficulties are pointed out. Nevertheless, it explains enough of the tectonic pattern to merit inclusion among our working hypotheses of causes of Cordilleran spread.