Geomorphologically in Tamil Nadu, three major units are recognised from west to east. The western part comprises the Western Ghats roughly trending North-South and marked by a continuous range of Hills, extending from Nagercoil in the south upto Nilgiri -Bilgirirangan Hills in the north and further northwards through Karnataka.
The elevation of these Hills ranges between 1275 m and 2637 m. The prominent Hills are Mahendragiri, Agasthiarmalai, Anaimalai, Palani and Nilgiris. Doddabetta with an elevation of 2637 m is the highest peak in the Nilgiri Hills. The east-west trending Palghat Gap is a prominent physiographic break in the Western Ghats. The central part of the state is a vast track of dissected pediments and pediplains.
Residual Hills in this part viz., Shevaroy, Kalrayan, Chitteri, Kollimalai, Pachchaimalai and Javadi demarcate the extensions of Eastern Ghats, while Karandamalai, Sirumalai and Kodaikanal Hills form another set of residual Hills, further south. The eastern part of Tamil Nadu and Pondicherry and Karaikkal are marked by a coastal plain with associated landforms like vast tidal flats, continuous beach ridges, estuaries and lagoons and a narrow but fairly continuous beach.