Landscape became deformed and I do not know how?

What happened? I was editing some landscape splines in one corner of my map. When I came back, everything was jacked up and the elevation was changed. It doesn’t appear to be the splines though. This happened once before and I spent 20 minutes flattening the land, only to come back to it and see its worse! Ideas?

http://imgur.com/a/rSB8b I’m having some trouble with the forum’s image upload - you can see in the picture, those green hills are on top of my roads!