Northeast of the village of Propouli, in the coastal region near the church of Agia Efthymia, impressive forms of erosion in the sandstone rocks are of the Upper Iocene – Lower Oligocene age.

The region is covered with sedimentary formations made up of sandstones and siltstones that were formed in underwater channels between 27 and 33 million years ago.

The honeycomb and basin-like formations seen in the sandstone layers across the coastal zone are the result of differential erosion caused by the action of water, waves, and the crystallization of salts deposited by sea spray are the primary causes of differential erosion.