The heights are characterized by a pronounced peak-and-trough surface relief, parts of which show formations from deep in the ground (kaolin).

Underground, the rock is formed mainly out of the Rhenish Slate Mountains’ Lower Devonian shale, metamorphic sandstone and quartzite.

On top are found, often several metres deep, great layers of periglacial deposits much of which contains carbonate-free to weakly carbonate loess loam.

Well known in professional circles are the occurrences of soil erosion (gullies and similar channels) in broad parts of the community which began in historical times.

Hausen über Aar likewise had its first documentary mention in 879, when it belonged to the Niederlohngau and found its way into the ownership of St. Severus's Monastery in Kettenbach, which in the same year was moved to Gemünden in the Westerwald.