These earth pyramids are a very recent geological phenomenon, formed around 50,000 years ago, and were created by erosion from water flowing through the earth in a morainic deposit left behind by pieces of quaternary glacier from the Würm glacial period.
They are made up of a conglomeration of earth and small pebbles of various origins, packed together into a stable consistency, but still vulnerable to erosion from rainwater. The morainic deposit was covered by a landslide of large quantities of porphyry, which is how the pyramids were born: indeed, underneath, the ground is more compact and protected by erosion from the rain.