These plains extend from south of Lake Vänern eastwards, and are known for their rich soil, which have supported human agriculture for over a thousand years. After the last ice age this area was sea bed, and nutrient-rich sediment settled on the bed as thick layers of clay. The Västgötaslätten plains are a flat region where the variation in height in some areas (such as Varaslätten and Skaraslätten) is as little as 10 metres.
The bedrock beneath large parts of the Västgötaslätten plains is called the sub-Cambrian peneplain, and is relatively flat. The reason for this is that the bedrock was eroded to an almost flat surface some 600 million years ago. The peneplain was then flooded by a sea that covered it with layers of sediment. The peneplain was then exposed again by erosion, although remanantsof sedimentsremain in the various rock types of the table mountains, and most is covered by a layer of soil. This is what made Västgötaslätten a plains landscape.