The glacial period
The climatic variation which characterises the Quaternary period was due to changes in the Earth's orbit around the sun. Periodically, an increase would occur in the volume of the polar ice and the level of the oceans would recede, thus revealing large areas of dry land in the coastal regions.
At the peak of the last glaciation, Europe was divided into three major climatic zones. In the north, a glacial cap covered the land as far as the south of what is now England. Further to the south, an area of tundra was inhabited by a few animals and even fewer people, as it was glaciated throughout the winter. Finally, the most hospitable zone corresponded to an area now including southern France: the vegetation (lightly wooded steppes, thin Scots pine forest) was favourable to large herds of wild herbivores.
The landscape resembled the steppes of central Asia, with summer temperatures that could reach +15°. In winter they fell to -20°.
A mosaic of landscapes in southern France
In fact this latter zone was a mosaic of landscapes and microclimates: the land above 1000m was permanently covered with uncrossable glaciers; natural barriers to humans and animals. The Mediterranean coast benefited from a less severe climate than the Rhône Valley, which was swept by cold winds.
The absence of forest
All of the Alpine valleys overflowed with ice. At the front edge of this area, the almost total absence of forest was due above all to the prevailing aridity: the wind brought neither cloud nor precipitation but swept dust and loess from the ground and transported them over long distances to where they accumulated as layers tens of metres thick. These deposits rapidly buried human encampments and animal carcasses, which were then particularly well protected and preserved until the present day.
In the open landscape of the Ardèche, composed of plateaus cut by deep valleys, horses and reindeer could move freely over large expanses of territory naturally enclosed by relief.