Historical Features are physical or cultural features that are no longer visible on the landscape. Examples: a dried up lake, a destroyed building, a hill leveled by mining. The term makes no reference to the age, use, or any other aspect of the feature. A ghost town, for example, is not a historical feature if it is still visible.
Rapids - Fast-flowing section of a stream with turbulent flow, often shallow and with exposed rock or
boulders, wheredischarge is mostly influenced by velocity rather than width and depth
(dalles, riffle, ripple).