The ＇＇mountain front problem＇＇, a rapid loss of structural elevation and shortening at a homoclinal foreland-dipping panel, has been extensively discussed in recent years. One of the solutions to this problem, the ＇＇triangle zone＇＇, has been widely applied to fold-and-thrust belts. The type example of the ＇＇triangle zone＇＇ is at the eastern margin of the Alberta Foothills, The ＇＇triangle zone＇＇ is essentially a duplex in which the roof thrust has a backthrust sense of displacement. Similar structural complexes have been described as passive-roof duplexes, which is the terminology preferred in this paper. However, in many cases, the passive-roof duplex is a nonunique solution for the constraining data. Many of these mountain fronts may be pseudo-passive-roof duplexes, which have only the superficial geometric characteristics of passive-roof duplexes. Alternative models that consider basement involvement and/or inversion of pre-existing basin-controling fault systems are not always fully considered. The alternative models may be less prospective exploration targets because the potential for imbrication of the reservoir section is reduced. The detailed internal geometry of the passive-roof duplex at the mountain front of the Alberta Foothills is now well constrained by high-resolution data sets. This is not the case with many of the pseudo-passive-roof duplexes that have been described from other fold-and-thrust belts. It is possible that passive-roof duplexes may be less common in other thrust belts than is currently thought.