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.
At Spjutøy and Straumsosen there are three entrances from Lurefjorden to the fjord basin inside. Right up the end of the 1800s the ferry could not reach further than to Mølna at Spjutøy. At Skallestraumen there was a bark mill driven by the powerful tidal current in the sound. Here was also a store, a bakery and a hostelry place around the middle of the 1800s.