A triangle zone with an internal duplex developed in Cretaceous Colorado Group strata occurs in the broad Williams Creek Syncline in the footwall of the Burnt Timber Thrust (Township 29, Range 7W5). The triangle zone fills the role of a footwall-ramp-collapse duplex, since it is located in the footwall ramp of the Burnt Timber Thrust. We interpret this triangle zone to be a relict intercutaneous wedge based on the presence of a roof thrust that does not wrap over the duplex, the apparent absence of shortening transferred through the triangle zone towards the foreland and the younger structures below and east of the triangle zone. The kinematic relationship of the intercutaneous wedge with the Burnt Timber Thrust is not known and we distinguish three possible histories based on the presence and amount of out-of-sequence motion on the Burnt Timber Thrust, The relict triangle zone owes its preservation to its position south of an important lateral ramp in the hanging wall of the Brazeau Thrust. North of the lateral ramp, Paleozoic carbonates acted as a stress guide and as a strengthener within the thrust sheet and within the orogenic prism as a whole. Because of this additional local strength, smaller amounts of thickening within Cretaceous strata above and lateral to these carbonates can be attributed to a ＇＇strain shadow.＇＇ Since the thickness of Paleozoic strata and the great structural thickening within the Cretaceous section are both absent just south of the lateral ramp, the resulting regional plunge depression preserves the youngest strata and the shallowest structural levels in this part of the Foothills. The triangle zone relict occurs within these shallow strata. The presence of relict triangle zones indicates that a series of such structures formed at the leading edge of the orogenic prism.