South of the Mullaperiyar reservoir, at the source of Periyar River, there is an unbroken stretch of about of sheltered, unmodified rainforests within the Periyar Tiger Reserve. These rainforests extend further west into the adjacent Pamba basin within the Gudarakal Forest Range and continue south beyond the Gudarakal Range into the forests of the Achankovil Division. This entire stretch contains about of undisturbed wet evergreen forests typical of the Western Ghats. The forests on the upper reaches of Periyar are mostly inaccessible and is one of the least disturbed evergreen forests left in the Western Ghats.