[[Image:rhinegraben sat.jpg|thumb|275px|left|Satellite image showing the southern section of the Upper Rhine Plain and the rift flanks of Vosges, France, and the Black Forest, Germany.]]
The Upper Rhine Plain was formed during the Early [[Cenozoic]] era, during the Late [[Eocene]] epoch. At this time, the [[Alpine Orogeny]], the major mountain building event that was to produce the [[Alps]], was in its early stages. The Alps were formed because the continents of Europe and Africa collided. It is thought that because the collision was '''irregular''', the initial contact between the two continents resulted in the formation of dilational (extensional) structures in the [[foreland basin]] to the north of the Alps.<ref>Sengor, A.M.C. 1976. "Collision of irregular continental margins: Implications for foreland deformation of Alpine-type orogens", ''Geology'', 4, 779-782.</ref> The result was substantial crustal thinning, forming a major extensional ''[[graben]]'' and causing isolated volcanic activity. The '''stretch factor''' is estimated to be ~2.
===Rift flank uplift===
The northern section of the Rhine Graben is equally framed by somewhat lower mountain ranges, the [[Palatinate Forest]] on the western and the [[Odenwald]] on the eastern side.
The extension induced by the formation of the Alps was sufficient enough to thin the crust and provide suitable dilational conduits for magmatic and volcanic activity to occur. This resulted in the emplacement of [[mafic]] [[Dike (geology)|dykes]], which follow the general structural trend of the extensional faults. In addition, isolated volcanoes such as the Kaiserstuhl were formed.