Brutus, I see now.
Well, to be honest, I think what you have is not very far from what you're looking for? I just believe that if you leave out the plaster and add some water to your finger and shape the top of those "rows" there that you can easily get that look.
Add glue to your Celluclay, and acrylic brown paint. Maybe some small rocks--add the bigger ones later. But you should easily be able to make what you have already into what you want with just a little work, in my opinion!