The giant Teays River flowed through what is now a very wide and flat valley between Charleston and Huntington (and also continues across southern Ohio).

It was filled up with lake sediments—basically, mud and sand. This happened because huge glaciers to the north acted like a natural dam. The ice blocked the ancient Teays River near Chillicothe, Ohio, and the water backed up, creating a massive prehistoric lake. When the lake finally disappeared, it left behind all that sediment, which is why the valley floor is so broad and flat today.