The two peninsular rivers that flow through troughs are the Narmada and Tapi rivers. These rivers flow through rift valleys or troughs formed by geological faulting and subsidence. Both rivers flow westwards and form estuaries when entering the sea, mainly draining into the Arabian Sea. Narmada flows through a rift valley between the Vindhya and Satpura ranges, originating from the Amarkantak hills. Tapi originates in the Satpura range and flows through a similar trough before entering the sea. They are unique among peninsular rivers for flowing through such geological troughs, unlike most other peninsular rivers which generally flow eastwards towards the Bay of Bengal.