Not sure what you mean but I guess you just need to find a node in the node network view that is responsible for this terrain (color) feature. Is it a SSS that creates these rims by any chance?
If you are unsure of what is causing it, simply disable or delete the nodes until the feature in question disappears. Then you'll know. It might be tricky though - you may accidentally deselect the general feature that may lead up to this arrangement.