Réserve naturelle nationale de la haute-chaîne du Jura, National nature reserve in Eastern France.
The Réserve naturelle nationale de la haute-chaîne du Jura is a 10,800-hectare protected area on the Monts Jura anticline, the highest chain of the Jura massif, in the Ain department. It stretches from the Swiss border below La Dôle to the Rhône cluse, between the Valserine valley and the Pays de Gex. Its 18 communes include Gex, Divonne-les-Bains, Mijoux and Lélex, and it rises from 500 to 1,720 metres.
The area formed through tectonic movements during Alpine mountain building roughly 20 million years ago. Glaciers then shaped the current landscape with its valleys and slopes during the last ice age.
The area maintains traditional mountain farming through controlled grazing that helps preserve high-altitude grasslands and local wildlife. These practices shape how the landscape looks and how people in surrounding villages interact with the land.
Visitors can use marked trails throughout the year, accessible from several towns including Gex, Divonne-les-Bains, and Thoiry. Wear sturdy footwear and check weather conditions before visiting, as the elevation means conditions can change quickly.
The reserve covers 10,800 hectares across 18 communes of the Pays de Gex, yet no commune lies entirely within it. It is the fourth-largest national nature reserve in metropolitan France, created by ministerial decree on 26 February 1993. Its forests cover about 7,989 hectares, more than 73% of the territory.
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