Geology
Around 35 million years ago, a rift valley of about 300 km long and 50 km wide came into being between the present cities of Basel and Frankfurt. This was due to tensile stresses in the Earth's crust and mantle, which resulted in lowering the earth's surface. The moat has been partially filled up again by sedimentation. On the edges we find mountain ridges, the so-called "rift flanks". On the Eastern side, they are the Black Forest and Odenwald mountains, in the West the Vosges and Palatinate Forest. During the tertiary, the High Rhine continued West from Basel and flowed via the Doubs and the Saône, into the Rhône. The rift diverted the Rhine into the newly formed Upper Rhine Valley.
The Rhine knee at Basel marks the transition from the High Rhine to the Upper Rhine with a change of direction from West to North and a change of landscape from the relatively small-chamber high-Rhine cuesta landscape to the wide rift zone of the Upper Rhine Rift Valley. The two largest tributaries come from the right: the Neckar in Mannheim, the Main across from Mainz. In the northwest corner of the Upper Rhine Valley, at Rhine-kilometer 529.1, near Bingen, where the Nahe flows into the Rhine, the Rhine flows into a gorge in the Rhenish Massif and thereby changes into the Middle Rhine.
Read more about this topic: Upper Rhine