displacement trimming

I made a hill on a fairly big chunk of flat ground, but now that i have made the hill, is there any way to remove the flat parts surrouning it? (i want to copy it and put them together)

I tried carving...which didn't work, it did some really wierd stuff.

Any help is appreciated
Thanks

Have you tried clipping without deleting, so that you just sperate
them? That might not mess up your desired displacement and then you
could delete the extra.

displacement surfaces MUST have 4 sides. so you can clip them, but it has to be full edges at a time. no chopping little corners off, or like you say, wierd stuff will happen.

thank you guys....I had just never really used the clip tool....I was trying to carve......Wow I'm an idiot, thanks for the responses