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 above the ground, causing the bases of outcrops to erode more rapidly than their tops. Running water can have the same effect. An example of this type of mushroom rock is the one in Timna Park, Israel.