I have an interest in the distribution of stress in the upper crust as a product of topography. I am also interested in the role of material strength on topographic evolution, specifically for regions with tectonically driven localized strain weakening. Topography is a product of non-linear coupling between tectonic and surface processes. The topographic patterns we see are dominantly predetermined by the three dimensional spacing and orientation of strength heterogeneities, which may originate from tectonism. Surface processes such as river incision preferably erode surface exposures of weak zones and form ridge/valley geometries. Valleys have relatively smaller vertical normal coordinate stresses and therefore require a lower critical shear stress for failure causing a further weakening of the valley walls and floor. The non-linear coupling between tectonism and river incision causes vertical advection and thinning of crust beneath the valley floor, contraction of the geothermal gradient and upward rise of the asthenosphere, further reducing rock strength in valleys.