The Don volcano (or rock) is a basaltic neck of which all that remains today is the chimney cap, which rises to 1165m. Its associated flows now form an inversion of the relief.
The Don volcano is one of the ancient volcanoes of the Ardèche. It is a basaltic neck that has been totally eroded away from the rest of the volcanic edifice (a neck is an old volcanic chimney that has been preserved by erosion to a greater extent than the rest of the structure). It is characterised by its highly variable prisms (sometimes vertical, sometimes horizontal). This particular prism indicates that this is the upper part of the neck, possibly a former lava lake occupying the floor of the original volcano.
The flow emitted by the volcano is also in reverse relief. It occupies a paleo-valley with an overall north-east/south-west orientation, and shows the different directions in which the lava flowed. Along route 204, you can see the granite that was baked on contact with the flow: it takes on a brick-red appearance and has a fairly crumbly texture.
During the Quaternary glaciations, the neck was extensively altered and broken up by gelifraction (fracturing of the rock by ice), resulting in significant scree, which can be seen around the neck and particularly on its southern flank.
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