The Odenwald (ˈoːdn̩valt) is a low mountain range in the German states of Hesse, Bavaria and Baden-Württemberg.
The Odenwald is located between the Upper Rhine Plain with the Bergstraße and the Hessisches Ried (the northeastern section of the Rhine rift) to the west, the Main and the Bauland (a mostly unwooded area with good soils) to the east, the Hanau-Seligenstadt Basin – a subbasin of the Upper Rhine Rift Valley in the Rhine-Main Lowlands – to the north and the Kraichgau to the south. The part south of the Neckar valley is sometimes called the Kleiner Odenwald ("Little Odenwald").
The northern and western Odenwald belong to southern Hesse, with the south stretching into Baden. In the northeast, a small part lies in Lower Franconia in Bavaria.
The Odenwald, along with other parts of the Central German Uplands, belongs to the Variscan, which more than 300 million years ago in the Carboniferous period ran through great parts of Europe. The cause of this orogeny was the collision of Africa’s and Europe's forerunner continents.
In the Triassic, about 200 million years ago, the land sank again, forming the Germanic Basin in which the metre-thick layers of red sandstone could build up. These were later covered over with layers of muschelkalk from a broad inland sea, then followed by sediments from the Late Triassic (or Keuper). The South German Cuesta Land thus formed.
When the land in the Odenwald was uplifted again about 180 million years ago, more than 100 m of the sedimentary layering, in parts, was eroded away down to the bedrock, as can still be seen in the western Odenwald. The bedrock here is composed of a number of different rocks, among them gneiss, granite, diorite, gabbro in the Frankenstein pluton, and so on. In the eastern Odenwald, the red sandstone is all that is left of the sedimentary mixture. Farther east in the Bauland, the muschelkalk deposits still overlie the Early Triassic layers. Furthermore, in the south near Heidelberg, there is still Zechstein under the Early Triassic deposits.