The Hegau region, situated at about
a.s.l., is surmounted by nearly a dozen
conical hills, which are between and high and which correspond to the remains of the
pipes of past volcanoes. The area was volcanically active during the
Miocene epoch. Much later, during the
Riss glaciation (
Pleistocene epoch), about 150
ka ago, the Hegau region was covered by large glaciers, which over time eroded the softer rocks around the harder
basaltic rocks of the former volcanic pipes (an example of an
inverted relief). After the melting of the ice age glaciers, the landscape received its typical, modern-day appearance. In conjunction with the past volcanisms, several
maars formed in the area, which later filled with water to form lakes. The
sediments of these maar lakes preserve exceptional
fossils, for example of the early horse
Hippotherium primigenium or of the giant salamander
Andrias scheuchzeri. During the
Middle Ages, fortresses were built on top of several Hegau volcanoes. The arguably best-known of the Hegau volcanoes is the
Hohentwiel, on top of which lie the ruins of a fortress of the same name. The Hohentwiel is located next to the industrial city of
Singen. It is the southernmost of the Hegau volcanoes. To the north of it, there are nine other extinct volcanoes (see list below).
List of Hegau volcanoes ==Rock gallery==