Close to Gornji Vrhovci, old geological layers spoil the secret of an ancient river delta. Where the river met the Pannonian Sea―sandstone, 'pelite' (fine claystone), and 'tuff': a volcanic ash rock, are found. On some places the deposits can reach a thickness of up to 350m, influenced by periodic sea connections. These deposits originate from the Ottnangian-Karpatian period, roughly 18 million years ago. Sand and gravel from the Papuk Hills are mixed with remains of molluscs, corals, and tiny 'foraminifera'; and this evidence proves it once was the coastline.
Part of: Geosites in Papuk