Holmengrå is the only place in Hordaland where we find traces of the abrasion that is supposed to have transformed Western Norway from a Himalaya-like high mountain landscape during the earth's Paleozoic Era, to a flat lowlands terrain during the Mezosoic Era. Just 400 million years ago, large and small stones plummeted down from the high mountains. Some of these stones became incorporated into the conglomerate bedrock on Holmengrå.
Mangerite is a rock type that was first made famous in a treatise by the Bergen geologist Carl Fredrik Kolderup in 1903. The rock type got its name from the place where it was found, and has made the Mangerud name well known around the world, at least among geologists.