Living sandstone's tafoni

Sandstone is almost like a living creature in its infinite changeable character. It seems impossible that the formations can come from only the forces of wind, rain, chemical weathering and ice. I sometimes try to imagine how weathering alone could have produced such a variety of shapes and forms. Like almost everything in the world, there is a name for this type of formation, tafoni. No one really knows how they form, but the most favored current explanations involve salt weathering, differential cementation of the grains, and/or structural variations in permeability

At about 6000 feet above sea level here is a photo of a fine grained Moenkopi sandstone with a pronounced tafoni formation.