Recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation. Between provinces the state of stress may undergo substantial changes, often over remarkably short distances. As analyzed here, the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic-brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility. The component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other, whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes. The horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction: thus, in this regard, states of stress in adjacent domains appear to be coupled. The coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic-brittle layer in the direction of increasing horizontal compressive stress. This analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic-brittle layer.