The Shuswap core complex records Mesozoic and Paleocene crustal shortening with superimposed Eocene extension. During the shortening phase the crust was thickened and slowly uplifted. Within at most 20 Ma of the climax of compression, the crustal welt was rapidly uplifted and tectonically denuded.Shortening of the continental crust may be balanced in the underlying lithosphere by thickening or underplating, forming in either case a lithospheric root beneath the crustal welt. We consider a model whereby Tertiary crustal extension in the Shuswap core complex, and possibly also in other segments of the North American Cordillera, is accounted for by the detachment of this root. Both the time frame and the stress field resulting from the detachment are compatible with geological and geophysical observations. Far-field stresses played an accommodating role, but the potential energy required for extension of the Shuswap complex was induced by lithospheric thickening.