Layered Dirt Wall

These are the textured dirt backdrops the underground generates on its own, decorative variation on the plain version and nothing more. Clearing one leaves no item, so the pickaxe route does not exist. The only supply is crafting, which catches out anyone who assumes a wall they can see is a wall they can collect.

The difference matters once you start building. Anything the world placed counts as unsafe and enemies keep appearing in front of it, while the same wall hung by your own hand blocks spawns like any normal building material. A cave you cleared out and moved into is not actually quiet until every original panel has been covered or replaced, and the crafted versions let you do that without the room losing the look you moved in for.