The upper part of the Periyar basin extends across the Cardamom Hills. In the north, these hills extend up to the high Munnar saddle running east to Chokkanad Mala and further on to Kolukkumala on the eastern edge of the Ghats. In the south, the hills reach up to the westerly spur at Chokkampatti Mala. This section of the basin is divided into three parts.