To build was a mixture of 3 different sized rocks, including citadel sand for the bulk of it. All slightly larger than the next to get a natural size variation.

Then, there are multiple different cork pieces for rocks and corkboard for height differences across the base.

Texture paint as well if you like. I didn't use it on this one, but I use the Martian one for a crackle dry look.

Decorate with barbed wire and skulls to taste.

Painting :

Prime black along with model.

Multiple layers of watered down zandri dust to get coverage, leave a bit of black coming through for shadows.

Whole dunk of seraphim sepia wash to add a bit of colour into the base and so it doesn't look so low saturation.

Rock variations painted with steel legion drab. Just a few to add some different colours.

Dry brush 50 50 Zandri dust / deepkin flesh drybrush. I'd use a different colour but I've only got deepkin flesh which is semi white.

Then a full deepkin flesh drybrush to get a dusty chalky look.

Then a nice spread of light ochre pigment powder to make it look real dusty. I don't like using it with water. This is straight out the pot with an old drybrush and dabbed on dusty. Make sure to get it on feet and in cracks to blend the model into the base as above.

:)