Setting the Scene, Rocks

 I added a cylinder to be the first of the long rocks to be about the map for manoeuvring between.

Once it was changed to a editable poly, I moved the vertices at the top of the cylinder to give it a rough edge and then added a displace modifier, like for the terrain and added a height map for a canyon face which can be found here.

This looks ok, the result could be better with more clusters and mounds of rocks of this shape much like the original picture of Iego.