Where in France is the novel Malevil based on, written in 1972 by Robert Merle? The book not the movie based on it, and the French original preferential to the English translation since there are differences in distances between the two. I'm looking for a precise geographical location, within a dozen kilometers or so. I realize that the actual castle and main village are probably fictional, but the novel does include references to other nearby locations.
Clues from the book:
General clues: The area is rural France, has chestnut forests, and can grow wheat, wine grapes, cows. The prevailing wind is from the West. The characters native to the area speak with an accent described as "our own broader Southwestern (with a hint of Massif Central) sounds" or "notre accent du Sud-Ouest (qui tire un peu vers le Centre)" Some characters speak in local patois, of which there seems to be only one (slurred?) example: "Memima, Emamouel" with the French translation of "mélfie-toi Emmanuel!", "beware", or "look out!".
Geographical clues: From the titular Malevil (English-style) castle, Malejac village (pop 400+) is 1.5 km away; La Roque is an old fortified town on a hillside 15 km away; and the town containing the nearest express train station is 60+ km away. Saint-Sauveur is another nearby town. Downhill from La Roque through Malejac to the Rhune river ("fleuve" in French, so it flows into an ocean or sea, not into another river). The Rhunes are twin rivers, running north to south in a 100 meter wide plain between two lines of wooded hills. There is also a cliff to the north that protects the castle, and volcanic rocks push up through the soil. Another castle, the Château des Rouzies, is on the far side of the valley.
I've gone about as far as I can, narrowing it down the area the author based this novel on to somewhere in the Nouvelle-Aquitaine or western Occitanie regions. I've been comparing the English and French versions of the novel(although French is not one of the languages I know.) I would appreciate an answer that either nailed down the precise local dialect, or used the geographical clues to at least get down to the department level. I'm hoping that someone either francophone or familiar with Southwest France can shed further light.