Monolith

A monolith is a geological feature. It is a massive stone or rock. 

Erosion usually causes the geological formations, which are often made of very hard and solid igneous or metamorphic rock.

In other words, a monolith is what's left after most of an original rock or mountain is worn away.

Other websites
 Regarding Uluru/Ayers Rock and earlier representations of it as the largest monolith: GA.gov.au, ABC.net.au, Wayoutback.com.au

Category:Geological formations