Four crust types have been recognised on badland slopes developed in Miocene marine marls of the Guadix-Baza depression. The pediment crust, is depositional in origine and is found on the surface of gently sloping pediments flanking the steep
badland slopes. The other three crust types, domed, tower and pinnacle developed in sequence on the steep gully side slopes. An integral part of the crust development sequence is the progressive colonisation of the surface by blue-green algae and lichen