There are least 79 named Pillars in Wyoming according to the U.S. Geological Survey, U.S. Board of Geological Names. A Pillar is defined as a "vertical, standing, often spire-shaped, natural rock formation (chimney, monument, pinnacle, pohaku, rock tower)". The Oxford Dictionary of Geography defines Earth Pillar as "an upstanding, free column of soil that has been sheltered from erosion by a natural cap of stone on the top". They are common where boulder-rich moraines have been subject to gully erosion, as in parts of the southern Tyrol.