In the Sandhem-Halvorstorp area we see large areas where flat outcrops of bedrock are exposed. In some places the bedrock here is more than 1.6 billion years old! The flat surface (peneplain) was formed by erosion more than half a billion years ago. Only very primitive forms of life existed then, and there was no vegetation on the Earth. This flat surface is called the sub-Cambrian peneplain, because it was formed before the Cambrian period. The peneplain was then buried by thick layers of sediment from a sea that flooded the peneplain.
These sediments have now been completely eroded away here, but remains can still be seen in the rocks of the table mountains (for example on Halleberg and Hunneberg). In other words you are standing on a flat rock surface that was formed over half a billion years ago but which was once buried under deep layers of sediment! At Slättbergen you can also see traces of the last ice age, when ice and stones gouged the rock surface, leaving ice grooves that show the direction the ice was moving.
Slättbergen is a municipal nature conservation area, divided into three nature reserves in, or adjacent to, the town of Trollhättan.