User blog comment:SmokedSausageFTW/The Forest Development Blog 5/@comment-13254338-20140708033143/@comment-13254338-20140708034244

Actually Lumage, the generator might not use any kind of noise. It appears that it has something along the lines of:

hill_Y =  hill_Y + < a random number between -3 to 3 >

If it WERE perlin noise, the hills would look more circular.