Many of the native american dwellings at mesa verde and elsewhere in the western united states are located under overhangs that form along the contact between permeable and impermeable rock layers. these overhangs (niches) were primarily created by what process?

The answer is salt-crystal growth. The  granular deterioration or discontinuity of shake material delivered by salt-precious stone development. This implies there is salt crystallization in exceptionally permeable stones. Salt weathering is a type of mechanical or physical weathering of shake. No compound change of shake constituents is associated with salt weathering. The salt gets from an outer source.