For something like that you can use different methods. I'd say: take a terrain that you like, add a lake and find a nice POV at the water's edge, with the small mountains across. Then add a distance shader and blend/mask the larger mountains by the distance. If you don't want the smaller mountains and larger mountains intermingled, blend the small mountains inversely by the same distance shader. Something like that. You can also use simple shape shaders to mask the different terrains and water area. Lots of methods.
