Historically, Hegau was a Gau of the Duchy of Swabia, first mentioned in 787 A.D. in the Latinised form in pago Egauinsse.

Today, Hegau refers only to that part of the former Gau which is located within the German state of Baden-Württemberg.

'Hegau conical hill landscape'), is a Young Drift morainic landscape marked by the remains of several extinct volcanoes, the Hegau volcanoes, which are located mostly to the west and east of the line from Singen (Hohentwiel) in the south to Geisingen in the north.

After the melting of the ice age glaciers, the landscape received its typical, modern-day appearance.

The sediments of these maar lakes preserve exceptional fossils, for example of the early horse Hippotherium primigenium or of the giant salamander Andrias scheuchzeri.