New structural mapping and seismic interpretation indicate that the triangle zone and related structures exposed along and adjacent to the Oldman River, southern Alberta Foothills, comprise a complicated structure involving significant deformation in the hanging wall of the upper detachment. This deformation includes orogen-directed thrusts and large orogen-vergent folds (ca. 1 km amplitude) as well as apparent secondary orogen-directed tectonic wedging. Although duplex structures are interpreted to occupy the interior of the triangle zone, the term ＇＇passive-roof duplex＇＇ is inappropriate due to the degree and nature of deformation above the upper detachment. The upper detachment is best viewed as a structural domain boundary, separating dominantly foreland-directed structures below from dominantly orogoen-directed structures above. Multiple levels of detachment have resulted in two ＇＇nested＇＇ tectonic wedges which show evidence for some synchronous deformation. Our interpretation suggests that a relict triangle zone toe may be preserved and exposed along the Oldman River, immediately above the principal upper detachment (the Big Coulee Fault).