Colomby de Gex
| Colomby de Gex | ||
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 Colomby de Gex |
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| height | 1688 m | |
| location | Ain , France | |
| Mountains | law | |
| Dominance | 5.56 km → Grand Crêt | |
| Notch height | 248 m ↓ Col de Crozet | |
| Coordinates | 46 ° 19 '20 " N , 5 ° 59' 43" E | |
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At 1688 m, the Colomby de Gex is the fourth highest mountain peak in the entire Jura (if the Grand Crêt is counted as an independent peak). It belongs to the Haute Chaîne , the easternmost and highest chain of the French Jura, and is located in the Pays de Gex (Département Ain ), around 17 km northwest of the city of Geneva above Gex .
The Colomby de Gex is bounded in the east by the plain of the Pays de Gex and in the west by the valley of the Valserine . The ridge of the Colomby de Gex slopes steeply in these two directions. It rises directly from the plain of the Pays de Gex without a foothill zone and towers over the Geneva basin by around 1,200 meters. The wide ridge is made up of several peaks lying next to each other in a line, each reaching heights between 1610 m and 1688 m . To the northeast, the Jura ridge leads to Mont Rond and finally to Col de la Faucille . Towards the southwest, the Colomby de Gex is separated from the Grand Crêt and the Crêt de la Neige by the saddle of the Col de Crozet ( 1480 m ) .
From a structural and geological point of view, the Colomby de Gex forms an anticline of the Jura folds , whereby the rock layers were pushed onto the sediments further to the west at the time of the Jura folding in the late Miocene and Pliocene . The anticline is around 6 km wide at the root and is oriented in the direction south-south-west-north-north-east in accordance with the strike direction of the Jura chains in this mountain section. The anticline has broken to the northeast of the main summit. The rock material was removed and over time a deep excavation basin was created , which is now drained by the Torrent du Journans (in the Allondon catchment area ). The upcoming rock material of Colomby de Gex comes from marine sediments of the upper Jurassic period (in the comb area are mainly the dolomitic limestones of Port Landien , the limestone beds of Kimmeridgian and Sequanien ago) and Cretaceous (mostly at the foot of the slope).
Due to the limestone , various karst phenomena could develop on the ridge of the Colomby de Gex . There are numerous sinkholes and cart fields here ; The rainwater seeps into the porous subsoil and mostly only reappears at the foot of the Jura range in karst springs (for example in the Allondon spring). That is why the slopes of the Haute Chaîne show very few surface running waters. Some Karmulden on the eastern slope of the summit chain bear witness to the Ice Age glaciation .
The summit area of Colomby de Gex is grassy and shows subalpine vegetation. Mountain pastures predominate above about 1,400 m, with a coniferous forest zone below that, which in turn is replaced by deciduous forest below about 900 m. The Colomby de Gex is a panoramic mountain of the High Jura; on clear days there is an impressive view over the Geneva basin and Lake Geneva to the Savoy Alps with Mont Blanc . The Colomby de Gex is part of the Parc Naturel Régional du Haut-Jura and the Haute Chaîne du Jura nature reserve .
