South India is a peninsula in the shape of an inverted triangle bound by the Arabian Sea on the west, by the Bay of Bengal on the east and Vindhya and Satpura ranges on the north. The Narmada river flows westwards in the depression between the Vindhya and Satpura ranges which define the northern spur of the Deccan plateau. The Western Ghats run parallel along the western coast and the narrow strip of land between the Western Ghats and the Arabian Sea forms the Konkan region. The Western Ghats continue south until Kanyakumari. The Eastern Ghats run parallel along the eastern coast and the strip of land between the Eastern Ghats and the Bay of Bengal forms the Coromandel region. Both the ranges meet at the Nilgiri mountains. The Nilgiris run in a crescent approximately along the borders of Tamil Nadu with northern Kerala and Karnataka, encompassing the Palakkad and Wayanad hills and the Sathyamangalam ranges, extending on to the relatively low-lying hills of the Eastern Ghats on the western portion of the Tamil Nadu-Andhra Pradesh border forming the Tirupati and Annamalai hills.