modcap

Doing my first substantial terrain edit to the Tamriel Worldspace and when sculpting a bit into the side of a mountain I ran into this "layer" of landscape that the push/pull tool doesn't effect. Can anyone tell me what this is and how to negotiate the editing of it? Edit: I should specify that I'm pretty darn sure it's not a mountain face. It doesn't appear to be selectable from any angle, even when I move all of my added elements away from it. http://i.imgur.com/IPDO2wL.jpg Pic shows it in CK and in-game. New CK for SSE. All vanilla assets so far. Edit2: Even just telling me what it is called would help me google it further. Thanks.