The Dundas Valley was initially carved into the Niagara Escarpment by a preglacial river, but was later widened band depended by intense ice scouring to create the present broad U-shapped form characteristic of glaciated valleys. Deepening was so extensive that in the lower reach of the valley the bedrock surface now lies in excess of 100 meters below the level of Lake Ontario. Vast glacial till, meltwater and lake deposits now deeply cover the area and completely bury the Escarpment rocks in the upper portions of the valley.