Karavali-Malnad - Region

The central portion of the Western Ghats - Super-Region is divided into 2 distinct Regions :

Karavali - Coastal

Malnad - Upland

The Karaval - Region / also called "Coastal Kannada": comprises of Tulu Nadu in the south and Haiva Nadu in the North. Tulu Nadu is Coastal Plain and Haiva Nadu is Coastal hills (the southern most extent of geological Konkan which is mainly coastal hills).
The Varahi river is the geological boundary between Tulu Nadu and Haiva Nadu, from there the hills branch out to the north in contrast with the plains to the south - though I do not information as to the ethnic/cultural boundary between the 2 regions. The plains altogether end at Baindur which is sometimes considered as the boundary between the 2 Sub-Region. It is likely that between the Varahi river and Baindur is the buffer/mixed area of Tulu and Haiva Nadu. The only ethnic difference between the 2 (that i am aware) is that Kannda is primarily spoken in Haiva Nadu, while Tulu is spoken in Tulu Nadu.

Geologically the Malnad - Region extends and includes the Malayalam speaking - Vynad and Tamil speaking - Udhagai regions.

Malnad - all Kannada (and related speaking) Forested areas of the Western end of the Dakshina Plateau. Geologically "Malnad" is the southern half of the Sahyadri mountain range and includes Vynad and Udhagai - but since these latter regions are not Kannada speaking have been included in Malaya Nadu - Region.
The word Malnad is a corruption of Malay Nadu - "Malaya" being the actual name of the entire Western Ghats, though the term "Malay Nadu" came to be refer to / was taken by Cherala.
Apart from the ethnically, linguistically and culturally distinct Kodagu region in the south part - the rest of Malnad can be divided based upon geology and the degree of deforestation.
Deforestation in the Malnad is often not acted upon and thus the the forests of Malnad are at grave threat.areas of Malnad join the bare plateau to the east.