#ravine  a deep narrow steep-sided valley (especially one formed by running water)
  supertype:  valley__vale  a long depression in the surface of the land that usually contains a river
  subtype:  canyon__canon  (North America) a ravine formed by a river in an area with little rainfall
  subtype:  gorge  a deep ravine (usually with a river running through it)
     subtype:  gulch__flume  a narrow gorge with a stream running through it
     instance:  Grand_Canyon  Olduvai_Gorge

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