Poldokhtar-Ilam path runs along the hillside of the Grub valley in the Kabir Kuh Mountain within Ilam province for approximately 4 km after Chenarbashi village. River flows in a deep gorge which is called “Tange Razianeh” and makes this gorge one of the tourist attractions in Ilam Province. For the exceptional nature of this region, it has been recognized as one of the natural heritages in Iran.
Grub valley is actually a syncline lays between two Kabir Kuh and Sartang synclines and Grub River is flowing across the youngest formation in this area- Gachsaran – with miocene age. It has made a series of vaporized rock layers such as salt and gypsum, along with marl and calcareous sedimentary sequence.