 Erosion is a common phenomenon in the river valley; there are many lakes and sloughs.The first of Tubutulik River, like the lower course of the Fish River, is a tortuous channel through alluvial flats built out from material that it brought down from its upper course.After the flats, there is a more restricted valley with the high hills of the Cape Darby granite area to the west and the softer forms of the limestone and schist on the east.