Mushroom rock

Usually found in desert areas, these rocks form over thousands of years when wind erosion of an isolated rocky outcrop progresses at a different rate at its bottom than at its top.

Abrasion by wind-borne grains of sand is most prevalent within the first three feet (0.9 m) above the ground, causing the bases of outcrops to erode more rapidly than their tops.

For example, erosion attributed to chemical weathering at the base of the rock due to the collection of dew near the surface.

This means that the combination of highest sediment loads and fastest wind speed exist a few feet over the ground, leading to the characteristic narrowing of the support pedestal at this height.

The lower part of the rock formation might or might not have also undergone a degree of erosion to accentuate the mushroom shape.