The weathering and different agents of erosion – rivers, winds, glaciers, etc. are constantly acting on the earth’s crust.
The process of erosion depends on the shape and structure of the rocks.
Due to the agents of erosion, the softer rocks of the upland are eroded much more rapidly than the areas of harder rock.
After thousands of years, soft rocks are worn down into the sand and the hard rocks are left standing up in the area that has been reduced in height.
These are called residual mountains.
The residual mountains are also called relict mountains.
Examples of Residual Mountains in India are the Nallamala hills, Mahendragiri hills, the Aravali hills, the Javadi hills, the Veliconda hills, and the Palkonda range.