most canyons are formed by flowing rivers through erosion over long periods of time
canyon is not flow_terrain. canyon is not ravine. canyon is flow_terrain. member_of_undergrounds_canyons is canyon. river is flowing_body_of_water. canyon is valley. member_of_undergrounds_canyons is not canyon. group_of_canyons is group_of_valleys. rivers has flowing_water canyon is ravine.