Hills extends deep into but is clearly separated from the Pandalam Hills. The main Western Ghats watershed line forming the eastern border of the Cardamom Hills is highest to the southeast of the Kumily Gap. Here the High Wavies branch off towards north-west into Tamil Nadu, with some peaks reaching elevations of over along the border between Kerala and Tamil Nadu. Further south, the ridge along the watershed line is heavily forested. This part of the Cardamom Hills is called the Sivagiri Range and it extends south up to Chokkampatti Mala which is at the junction of Pamba and Periyar River basins. The southern boundary of the Cardamom Hills runs along a westerly spur hill starting from the Chokkampatti Mala which initially runs north and then turns northwest almost parallel to the Sivagiri Range. This ridge separates the basin of Pamba from Periyar. From its source near Chokkampatti Mala initially Periyar flows north between these two heavily forested ridges. The valley floor is at an elevation of and the ridges on either side often reach . This valley of Periyar at its source and the valley of Kunthi River in the Silent Valley are the only two forested higher valleys in the Western Ghats left intact even now. The Periyar Tiger Reserve is mostly within this southernmost part of the Cardamom Hills. Cardamom Hills plateau A poorly defined ridge that runs from near Chakkupallam (north of Kumily) on the border between Kerala and Tamil Nadu extending southwest to near Vallakkadavu segregates the upper reaches of Periyar from the rest of the Cardamom Hills. Immediately downstream of Mullaperiyar dam, Periyar cuts through this ridge. North of this ridge, the Cardamom Hills extend up to the high Munnar saddle. Here, east of the river channel, the undulating plateau rises up to the watershed line of the Western Ghats. This section drains into the Periyar through the Perinjankutty Ar and the drainage channel is essentially from south-east to north-west. This portion of the Cardamom Hills is on an average high. The northern edge of the Cardamom Hills bordering the High Range Plateau on the other hand slopes steeply to the south and is drained by Panniyar. The Panniyar joins the Muthirapuzha, which drains the High Range Plateau section of the Periyar Basin in the north. The crestline of the Cardamom Hills in this section along the border with Theni and Kambam, in comparison