Interpretation of seismic profiles in the southwestern Alberta Foothills near the Crowsnest Deflection delineates along- and across-strike variations of orogenic structures in the triangle zone. The overall structural geometry is dominated by an east-verging allochthonous wedge of Mesozoic rocks, overlain by west-verging thrust sheets of Upper Cretaceous and Tertiary rocks, and underlain by undeformed Paleozoic strata. The Big Coulee Fault, which rides within the Bearpaw Formation, represents the boundary between east- and west-verging structures and is the main upper detachment of the triangle zone. Strike seismic lines reveal evidence of major lateral ramps and folding of the Big Coulee Fault. Backthrusts above the upper detachment (e.g. Co-op, Waldron and Callum Creek) die out southward near Crowsnest River and folding of these faults decreases eastward. This suggests an eastward progression in the temporal development of west-verging faults above the triangle zone. In the vicinity of the Crowsnest Deflection, a major lateral ramp occurs in the lower detachment, as it cuts up-section to the north from the Blairmore Group to the Alberta Group. This is evidence for southward thickening of the allochthonous wedge, in addition to its eastward-tapering geometry documented along the entire fold and thrust belt.