Basically found stock photos of real rocks, and snow and blended them together with the original image. The top before\after picture is actually the original image coupled with a picture I took of a section of my driveway

You'll notice on the Rocks 1&2 pictures, I basically planted a high quality picture of a rock texture in the middle, and erased around the edges, then I altered the color a bit so they blended a little bit more. I left the edges of the images as the original, so they blend well in-game, as in game the same texture is repeated over and over to fill up the area.
So basically, the middle of the texture is brand new, high quality and the outer edges are edited a tad bit to blend well and let the image fit together nicely in game.
Probably won't keep this in when I put the textures up for download, but I was screwing around with the wampa..

Edit:
Rebel Walls (In the Codes Area; Hanger)
Took the plain snow texture, and put a cement wall underneath it to make it look more like... a wall?
I'll probably mess with this one some more too.

Also- if anyone has any suggestions feel free to shout out.