Iron-rich minerals in rocks react with oxygen gas in the presence of water and form new iron compounds, such as iron oxides and hydroxides. This chemical process is known as oxidation or rusting. The formation of these new iron compounds causes the rocks to change color, appearing red, brown, or yellow. These rock formations often indicate areas with abundant oxygen and/or water during their time of formation in geological history. The reddish coloration can be observed in various geological features and locations worldwide, most notably in landscapes dominated by sandstone and iron-rich soils.