The bedrock consists of light and dark gneiss. Here you can see the results of a dramatic event that occurred a very long time ago. Kållandsö is part of an old fault zone in the Earth’s crust where the rock to the west was forced upwards over the bedrock to the east when we collided with North America a billion years ago. The bedrock to the west is also slightly younger than that to the east.
The results of this thrust can be seen today, just south of Läckö Castle, near Spiken and along the shore of Kållandsö. The type of rocks found here are heavily deformed (metamorphic), foliated gneisses which strike in north-south with a continuation across lake Vänern to Värmlandsnäs on the other side. Rocks of this type, which are heavily deformed by movement deep within the Earth’s crust, where temperatures are high, are known as mylonite. They are recognised by their very fine-grained, banded appearance.