This uplift created vertical joints, which over time were preferentially eroded. The soft Pink Cliffs of the Claron Formation were eroded to form freestanding pinnacles in badlands called hoodoos, while the more resistant White Cliffs formed monoliths. The brown, pink and red colors are from hematite (iron oxide; ); the yellows from limonite ; and the purples are from pyrolusite (). Also created were arches, natural bridges, walls, and windows. Hoodoos are composed of soft sedimentary rock and are topped by a piece of harder, less easily eroded stone that protects the column from the elements. Bryce Canyon has one of the highest concentrations of hoodoos of any place on Earth.