Making an Earthy Wall
Since this isn't terrain, it's associated with a specific Privateer Press wall size, they make a template available in the back of the rulebook. Rather than just photocopy this and use a paper template, 3D would look much more awesome.
I measured the dimensions from the book and cut a piece of Plasticard in those dimensions. Plasticard is basically a thin piece of plastic used in hobbying because it's easy to cut and provides a sturdy surface for heavier works like terrain.
It's a good idea to have a mini nearby for scale and image when working on terrain.
Then, as the start of the base, I 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: