After each flood, the water level fell slowly, depositing a thin layer of sediment across the flooded area. This marsh and pasture environment attracted many species of fauna. Four-metre-tall Megatherium (in the centre), glyptodons and Macrauchenia left their footprints in the fine, loose sediment.
This cycle was repeated dozens of times as each new layer of loose sediment recorded and then preserved tracks of animals. As the sea rose about 100 metres during the past 10,000 years, the ocean invaded the land, reaching Pehuen Co site. Today, tides are eroding the layers containing prehistoric tracks. Large areas are then exposed, providing astonishing views of ancient pathways. But the layers of prints are also vulnerable to irreparable damage from erosion and tourists.