The spectacular cliffs on the occidental coast of Gipuzkoa hide a singular natural treasure: millions of years of geolocic history written in successive rock strata because of the continuous action of the sea and have been finally uncovered.
They can be appreciated in all their best at low tide between the locations of Zumaya and Deva. The flyschs are rocks of sedimentary origin that alternate hard rock layers (limestone, shale or sandstone) with other softer ones (loams and clays). This mixture creates a differential erosion that firstly deepens on the soft layers, keeping upwards the hardest layers.
In Mendata and Sakoneta, the originally horizontal strata can be seen from a vertical view due to the internal movement of the soil in the Cretaceous. Also, in some of them, it's possible to see traces of fossil ammonites and other invertebrates occurring during the formation of the flysch.