This is great Ilanthar. I've been experimenting with relief shading styles too. I've put them into a couple of challenge maps, more specifically the Harpy's Silver Tongue one. It's in my albums.

I start by roughly drawing in contour lines in a sort of faded brown colour then I add more density where they're closer together, lighter where they are further apart. I use a dark colour in multiply mode. Then I start adding highlights on the other side using a light colour and screen mode. Then I hide the contours layer.