Majestic retreats
How can the formation of an alley be explained? By a series of phenomena which followed one another during the different geological eras... First of all, when the Jura was covered by the sea, layers of more or less hard sediments were deposited one on top of the other. Calcareous strata alternate with more marly ones. Then, during the ice age, faults were formed by the frost, more or less narrow and deeper depending on the nature of the layers. During the thaw, water infiltrates these faults. They stagnate in caves, slip through holes, dig capricious underground networks, and carry away stones and sand that erode the rock. In some places, they open a long gash in the limestone. The edges collapse. The underground waters come out on the floor below, continuing to dig a long, more or less narrow valley, between the cliffs produced by the collapse. Sometimes, as in Baume, different resurgences form "fingers" which join before separating towards the plain.
Waterways that shape the landscape
The region is a land of rivers. The Ain has its source here before joining the Rhône, forming a large dam lake at Vouglans. The Doubs crosses the north of the department. Several rivers have shaped the landscape, provided hydraulic energy and allowed the development of economic activities in the valleys: the Bienne, the Suran, the Valouse in the south of the department, the Cuisance in Arbois where Louis Pasteur's father set up his tannery, the Furieuse in Salins... Several rivers, waterfalls and bodies of water are classified as first category for fishing, like the Dessoubre valley. For river tourism, the Val d'Amour and the Loue, full of fish, stand out in the north of the Jura.
Trays
The first plateau of the Jura is situated between 500 and 600 m of altitude. The landscape is made up of large meadows, with winding roads linking the villages. The houses are built of stone, with steeply sloping gable roofs. Stone is found in the walls along the meadows and in the shepherds' huts. This plateau is in a way the "cover" of the caves and recesses of the lower level. Its geology and flora are characteristic: the hard rocks have remained on the surface and the softer ones have been eroded by water infiltration. This water has found its way to the lower level, but is hardly abundant in the vicinity and, in the absence of fountains, the inhabitants of this first plateau had to rely on a few wells or rainwater tanks before developing water supply systems.
Plains
Between Haute-Saône and Bresse, the lower part of the Jura is linked to the collapsed plains of Burgundy. It is a country of rivers, ponds and crops. To the north of Dole rises the small massif of the Serre. At an altitude of almost 400 m, it is an unusual area in the limestone Jura: its soil, a remnant of the primary era as opposed to the "Jurassic" which dates back to the secondary, is granitic like that of the Vosges, with sandstone and volcanic rocks. There are caves and even ancient quarries which have been exploited, it seems, since the Neolithic period.
Summits and passes
The Jura massif extends over several French departments and Swiss cantons. It has the shape of a crescent, oriented north-east/south-west. It is steeper on the Swiss side and is backed by the Alps. It was the thrust of the Alps that caused its formation. On the French side, it is tiered on several levels. Some peaks reach over 1,700 m, the highest being the Crêt de la Neige and the Reculet in the south of the massif. At their foot, the Haut-Jura Haut-Doubs plateau extends at altitudes of between 800 and 1,000 m.
Emerald green, bright blue, dark blue: lakes of all colours
The glaciers have not only carved deep valleys in the Jura plateaus, they have also carved out basins that have become lakes. The highest and shadiest lakes are sometimes frozen in winter, but in summer they are very popular, with water temperatures of up to 25°C. The lake region spreads over several levels: from barely 500 m for the lakes of Clairvaux and Chalain, to nearly 800 m for those around Frasnois and Bonlieu. Or even more, such as Saint-Point, Lac de l'Abbaye, Remoray and the small lakes in the Grandvaux region. The latter marks the limit between the lake country and the Jura Arc. Their surface areas are just as varied: the Saint-Point lake covers 5.2 km2 while others are between 25 and 100 times smaller. The vegetation and the appearance of the banks vary, sometimes easily accessible, where sandy beaches have been developed with areas suitable for water sports. Fishermen, hikers, picnickers and relaxation enthusiasts enjoy the shaded banks and the trails. From the viewpoint of the Chaux-du-Dombief or the Pic de l'Aigle (993 m), you can contemplate the "Four Lakes" of the Frasnois. The region of the Four Lakes becomes that of the Seven Lakes if we add the Vernois Lake, the small Fioget Lake and the Bonlieu Lake, further south, which feeds the Hérisson and its waterfalls. The Seven Lakes site and the Hérisson waterfalls are classified as a "Great Natural Site"
The wooded country
The forest occupies 47% of the territory of the Jura. It is one of the most forested departments in France. The origin of the name "Jura" attests to the omnipresence of the forest: it means "wooded country". The forest is diversified, depending on the altitude. Below 300 m, deciduous trees dominate: oak, hornbeam, ash and wild cherry. The forest of Chaux, between Dole and Salins, is a good example. The Serre massif is home to chestnut trees, rare in the Jura. From 500 m and up to 800 m of altitude, beech and maple trees mingle with conifers (mainly fir). The Joux forest, north of Champagnole, is one of the most beautiful fir forests in France. Higher up, the firs mingle with the spruces, which are increasingly present as the altitude increases because they like the strong light of the steep slopes.
Caves and chasms
Remarkable caves can be visited in the region, each with its own identity. They are spread over the territory, some accessible on the plateau like the Poudrey chasm or the Moidons caves, and others below like the Baume-les-Messieurs caves and those of Osselle.
