The inland ice was primarily responsible for creating the soft, welcoming landscape at Lake Hornborga. When the ice disappeared 10,000 years ago, it left behind it icebergs, hills and long ridges. Melting icebergs in motion created holes in the ground and gravel ridges with irregular formations developed around them.
At this time, Lake Hornborga was part of the sea. An inlet along the west coast of the as yet unborn kingdom of Sweden.
Just east of Lake Hornborga lies the Billingen table mountain, which consists of primary rock, sandstone, alum-shale, limestone, clay slate and diabase - in that order, from the bottom and upwards.
Limestone is important for Lake Hornborga. It guarantees that the lake will never become acidified.
The southern half of Lake Hornborga is surrounded by sand and gravel deposits with varying degrees of prominence. Between them, there are peat moors, land that was previously covered by the lake.