Canyon of Despair                                      -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      -      -

Here the canyon stops abruptly.  A large and unpassable wall of rock
stands in the way.  It must shoot at least 2000 feet in the air with a very
smooth wall.  The only way is now to the north.  The walls on the west and
east are not quite as tall but they are tall enough to block out the
sunlight.