During the Cenozoic era, 65 million years ago, the sea periodically invaded the Rhine ditch and deposited layers of sedimentary rocks (limestones, marls, evaporites, gypsum). They gradually filled it and reached a thickness of more than 8,200 ft (2,500 m). Later, in the Quaternary period (2,5 million years ago), the Vosges' rivers and the Rhine added river alluviums there, forming the Alsace plain.