Foreland basins are created by superimposed mechanisms that flex the lithosphere. In addition to static loads, dynamic loading below the basin by viscous mantle corner flow above a subducting plate may cause long-wavelength subsidence. It is proposed that the interaction of the static and dynamic forces is responsible for the formation and preservation of recently recognized “reciprocal stratigraphies” in retro-foreland regions above subducting slabs. Reciprocal stratigraphies refer to a correlative succession of strata characterized by contrasting stacking patterns that reflect opposite base-level changes between proximal and distal settings. The same interactions may also modify the stratigraphy of the flexural peripheral bulge and mask its presence. An example from the Late Cretaceous of the Western Interior basin, Canada, illustrates the concepts.