Jurassic (163-146 Ma), middle Cretaceous (103-99 Ma), Late Cretaceous (76-68 Ma), and late Paleocene- early Eocene (57-51 Ma), separated by quiescent periods of >40 Ma, >20 Ma, and >10 Ma respectively. The Rockies were uplifted during the Laramide Orogeny which occurred between 80 and 55 million years ago during the Late Cretaceous to the Early Paleocene as a result of subduction of the Kula and Farallon plates beneath the North American continent. Furthermore, the first radiometric ages obtained from direct dating of thrust-fault gouge from the front ranges of the southern Canadian Rockies identified two distinct deformation episodes named the "Rundle pulse" and the "McConnell pulse". These pulses were dated and are interpreted to have occurred at 72 Ma and 52 Ma respectively. Lewis Thrust System The Lewis thrust Is a low-angle thrust fault in which Precambrian sediments have been thrust over younger Cretaceous sediments. The thrust sheet is constrained by lateral ramps on either side. In the south this occurs near Marias Pass, Montana, where the ramp geometry is parallel to the direction of sheet movement. In the north, the thrust sheet is forced up and over an oblique ramp near the Kootenay Pass region in British Columbia. The overall shape of the thrust sheet as it moved north-eastward has a general convex shape towards the foreland. The Lewis sheet is carried by the Lewis thrust fault where the compression and thrusting (in the southern Canadian Rocky Mountains Foothills and Eastern Front ranges) was associated with oblique, right-hand convergence between the Intermontane terrane and the North American craton. This transpression in the Late Cretaceous led to the tectonic inversion of the Cordilleran miogeocline and the Belt-Purcell basin as the Lewis sheet began to buckle and fold, where strata was then overturned until a break or fault was formed. This involved thick successions of Paleozoic rocks that make up the Corilleran miogeocline and the underlying Neoproterozoic rocks to become detached from the crystalline basement; displaced up the passive-margin ramp along which they had accumulated; and juxtaposed over the flat surface of the North American craton to form the structural culmination that defines the Main Ranges of the Canadian Rockies. Similarly, the thick succession of Mesoproterozoic strata consisting of the Belt-Purcell supergroup followed the same sequence of events leading to the structural culmination seen in the southern end of the Purcell anticlinorium. The Lewis thrust is cut by two major extensional