Geochronologic, structural, and metamorphic data obtained from the hinterland of the Canadian Cordillera indicate that middle-crust ductile deformation was diachronous and coincided temporally with thrust propagation in the Rocky Mountain Thrust-and-fold Belt. Rocks currently at the highest structural level were deeply buried and then exhumed to upper-crust levels during the Middle Jurassic, when the orogenic wedge was in its early stages of evolution. However, structurally deeper rocks were buried and then exhumed at progressively more recent times, such that the deepest exposed level was not buried until the Eocene. This late stage of burial coincided with the final stages of accretion at the toe of the wedge. These observations are interpreted in terms of critical-taper theory. This theory suggests that, at the rear of the wedge, rocks were displaced from a basal high-strain zone to higher levels, where they subsequently cooled as they were exhumed from beneath the extending and/or rapidly eroding upper part of the wedge. A general conclusion of this analysis is that the localized shear zone that underlies the base of the wedge in the frontal part of the orogen becomes a transient feature toward the rear of the wedge. As underplating developed, rocks that were deformed within the basal shear zone were displaced upward to become incorporated into the overlying wedge and ultimately exhumed.