A "batholith" is just a collection of many granite intrusions, which are mostly underground. They do not have to be mountainous. In most cases they are covered by sedimentary rocks and you don't even know they're there. They only become mountains when you "fold" them. When you fold a piece of paper and it wrinkles, you have to separate the formation of the wrinkles (which happened now) from the manufacturing of the paper (which was in a paper factory, in the past).