I'm looking for "small" north-south box canyon style shapes in the terrain at the edge of the mountains.
Here is an example from one of @SirStafford's maps...
If that was all I wanted, I'd be done. Unfortuantely, I was hoping to find an example closer to the center of a world map (this one is pretty close to the edge), maybe with a lake above it that I could turn into a river running through the valley.
If anyone finds a likely example, please share. We aren't all nuts for islands here