Well, the main portion, besides the part hanging off the back, is just a terrain map, I don't know what to tell you lol. Other than the fact that it just takes a lot of playing around with the brushes. The main thing is to go into photoshop and put some splotches of white on a black canvas. These will serve as the high points in the ridges. You then use the smudge tool and a very large brush to drag from white to black To get long smudged lines that fade nicely on all sides, try to make these long, and curved. Once you have the entire thing painted like that, you blur it a little. Then to get the raised sections, take a square brush and do color dodge, this will raise up the entire section under the brush. It's 99% a lot of tweaking and playing around, trying to get it to look realistic. Much of my technique can be explained by the altitude map I posted above.