The area of the Seyne valley is dominated to the north-east by La Blanche mountains: from Dormillouse (2,505m) to Estrop (2,961m). These mountains separate the Seyne valley from the Ubaye valley. Their upper ridges are reinforced by the limestones of the Upper Cretaceous period, unevenly capped by the levels of the nummulitic limestone transgression.

In the Quaternary period, the Ubaye glacier, which came from the north via the Col de Saint-Jean mountain-pass, invaded the valley . During the maximum extension (Würm IV), the proglacial torrent flowed southwards through the Maure mountain-pass.

It was during this period that La Chau plateau was formed, which results in inclines of scree as well as large rocks and stones between the steep slopes and the glacier.

Glacial melt began here quite early, as evidenced by the pollens found in small peat bogs such as the one at Lake Saint-Léger.

As it melted, the glacier left numerous traces such as moraine veneers or large erratic blocks such as the Grosse-Pierre de la Liberne in Selonnet (a Haute-Provence UNESCO Global Geopark site).