During the course of the 1st tertiary, the formation of the Alps gave the valley its grand outline and its present shape. Later on, in the 1st quaternary, the successive glaciations finished giving it its present shape. 20,000 years ago, the Rhône glacier and the glaciers of the lateral valleys covered the ground up to an altitude of 2,000m. Due to these fluctuations, the latter left various traces in the form of moraines and glacial cavities. In the region of the plane of Tortin, two lateral moraines of the ancient glacier are clearly visible. These are the great and small Toit de Tortin (Roof of Tortin) that date back approximately 9,000 years. They are now covered again by vegetation and the flora of numerous different varieties, such as the "lys martagon" finds a favourable terrain there.
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