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.
Valestrand became a centre for the tanning industry in Osterøy; one of the old crafts that has developed into a local industry with many places of work. From the 1870s ever more ventures were started. Many of the large sea houses we see today around the bay have been places for tanning and leather enterprises.