To begin, I got the "wall" dimensions from the Hordes rulebook and cut a piece of plasticard. I glued some stones to it and filled in all around them with a few layers of heavy gel. I moulded the gel in a ways to seem like it's bursting from the ground.
What we end up with is basically rocks shooting up from the ground.
To finish the dirt off, I wash it with Devlan Mud and apply some highlights.
I dug through my various amount of grasses, moss and other materials and glued them around. I even found some small rocks to glue to the tufts of gel still shooting out of the ground and a little greens to add to them.
Here's an example of scale, including a tease of the model I've just about finished: