Thank you!
The hills were suprisingly easy to make, I started out hot gluing bark chunks to a carved blue foam form, but that took a fair while, in the end I made most of the mesas by gluing three layers of blue foam on top of a carved polystyrene base (that forms the scree slope around each mesa), scraping the surface of the cliff with a serrated knife to get the rock effect and carving out the deeper cracks with the handle of the same knife, then polyfilla-ing the joins of the layers, I then glued different grades of sand/pebbles on the top of the mesas and around the bases and painted. I think I would like to get a bit more colour contrast but am a little unsure how to do it, maybe some desert/alien planet type plant life?