Poldokhtar-Ilam path goes along Kabir Kuh and in the hillside of “Grub” valley-river. Approximately 4 km after the “Chenarbashi” village, the river flows in a deep gorge that is called “Tange Razianeh”. It’s one of the most tourist attractive areas in Ilam province. Incomparable nature of this area causes it to be on the list of Iran national heritage.
Actually, “Grub” valley is a syncline between and along two Kabir Kuh and Sartang anticlines. Therefrom, “Grub” river is flowing across the youngest formation in this area-Gachsaran-with Miocene age; It has made a series of layered evaporate rocks such as salt and gypsum, with marl and calcareous sedimentary sequence.