The International Union of Geological Sciences has recognised the incalculable geological value of the strata at the cliffs at Gorrondatxe-Azkorri beach (in the Basque province of Bizkaia), officially nominating it a "Golden Spike" site - the official world reference for stratotypes of the Lutenian period, replacing the one found in Paris. The spike is the label with which experts recognise those places with unique properties in the world of stratigraphy. The plaque was installed at a point on the beach where the strata are found, a geological formation dating back 48 million years.

During the Lutenian, Gorrondatxe-Azkorri beach, its rocks and sediments, and all its surroundings were submerged at the bottom of the ocean, at about 1,000 metres depth. The temperature in this part of the planet was warmer than now. Registered in those rocks are the innumerable episodes that have occurred throughout the formation and evolution of planet Earth and so part of its geological history is written, as it were, in these rock formations. It is a history full of events that geologists today are trying to reconstruct, investigating or "reading" the information which has been locked up for millions of years in the rocks which are now outcrops on the terrestrial surface. Their work involves ordering the formations on a time scale known as Geological Time Scales. These scales are a time framework of global validity and divided into intervals (Eons, Eras, Periods, Epochs and Ages) the definition of which is based fundamentally on Stratigraphy, i.e. on the study and interpretation of strata or layers formed in the rocks through the accumulation of sediments and revealed at the Earth's surface.

For geologists worldwide, the stratotype at Gorrondatxe has unquestionable value. Xabier Orue-Etxebarria, who began his investigations on the strata at Gorrondatxe in 1977, believes it to be "an exceptional, special place. This is why work was commissioned there and which revealed, amongst other things, two new fossil species which we have named bizkaiensis and gorrondatxensis, in honour of the beach there".

The President of the International Sub-commission on Palaeontology, Mr Eustoquio Molina, also highlighted that, in this way, "it is an incredible cut, very well exposed and one in which all the extracts can be demonstrated; it has enormous potential, having been formed 47.8 million years old. Any researcher interested in knowing what happened then should visit Gorrondatxe".