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Col de Porte

An article by Gérard Galland and Christian Jeandey

Le Col de Porte FR-38-1326b

Toponymy

Porte is the name of many localities, and the names of several communes begin with porte.
The catalogue of French mountain passes includes :

• 147 passes containing «Porte» in the full name (in various forms: Porte, Portes, Porteille, Portette , Entreporte, etc ...)
• 3 cols de Porte, 3 cols de la Porte, 3 Pas de la Porte (and 1 Pas de la Porte Étroite), 2 pas de Porte, 2 bocca alle Porte, 1 la Porte, 4 cols de Portes and 9 cols des Portes, etc...
• The term Porte is also used 22 times as a synonym for col.

Geographical location

Massif

The Col de Porte is located to the south of the Chartreuse massif.
This is the most southerly pass (and the highest point) of the north-south trough that crosses the massif (with the 3 passes: Granier (FR-73-1134 ), Cucheron (FR-38-1139) and Door).
It lies between the Charmant Som to the north-west and the Pinéa to the west (to the west of the D512), and Chamechaude to the east.
The two images from the geol-alp by Maurice Gidon illustrate the position of the Col de Porte.

Geology of the Chartreuse massif

The Chartreuse massif is made up of a pile of limestone and marl compressed and folded during the uplift of the Alps. The limestone is of marine origin, dating back more than 150 million years (Jurassic then Cretaceous). The relief is Alpine, resulting from the deformation of this sedimentary cover that began just over 20 million years ago. Over the last 2 million years, the cooling of the Earth's climate led to the periodic development of glaciers in the Alps. The massif was then occupied by enormous flows of ice, leaving only the highest peaks (Chamechaude, Grand Som, Mont Granier, etc.). These slow, powerful ice flows deepened and widened the surrounding valleys (Trouée des Marches to the north-east and Grésivaudan to the south). More than 1,000 metres of ice encircle the massif and sometimes overflow into its heart (at Saint-Pierre-d'Entremont), shaping the relief according to the strength of the rocks. The retreat of the glaciers has left a transformed landscape in which river erosion has now reclaimed its rights, carving out and reworking the moraine deposits. The last ice ages ended almost 13,000 years ago (Würm glaciation) [Geology of the Pre-Alps]. For specialists and more details, see Maurice Gidon's website.
Fluvioglacial and morainal deposits can most often be seen at the roadside in the valleys leading to the heart of the massif. The Col de Porte is the southernmost high point of the long «three passes» depression, which runs the length of the Chartreuse massif from north to south, carved out of the marls that bear the name Narbonne (hamlet of Saint-Martin-le-Vinoux).
It should also be remembered that the Chartreuse massif is karstic, meaning that there is a large network of caves and chasms (some 100 km of galleries) caused by the slow dissolution of limestone by water. These networks are the mountain's weak point which, combined with heavy rainfall, led to the major collapse of the Granier mountain in November 1248, and more recently to a series of landslides in May 2016.

Hydrography

• South side: the Sarcenas stream has its source near the Col de Porte and flows to the west of the D512 (between the Col de Porte and the Col de Palaquit (FR-38-1154b), a tributary of the Vence near Quaix en Chartreuse. The Vence flows into the Isère at Saint-Égrève.
• North side: the Ruisseau de Porte rises to the north of the pass and is a tributary of the Torrent de Fontanil, the Ruisseau des Corbeilliers and the Guiers Mort (at La Diat). The Guiers Mort converges with the Guiers Vif at Entre-deux-Guiers to form the Guiers, which flows into the Rhône downstream of Saint-Genix-sur-Guiers (Savoie).

Access

South side

From Grenoble, after crossing the Isère, you reach La Tronche on the right bank of the Isère. The Chartreuse road (D512) starts at the crossroads (altitude 233m), the Porte pass is 15 km away, it passes through Corenc (12 km - 468 m) before reaching the Vence pass (FR-38-0782) 8.5km away, then Le-Sappey-en-Chartreuse (4km, 1045m). The road then passes the Col de Palaquit (FR-38-1154b) (2.5 km away).
There are two possible variants:
From Grenoble, Porte de France, the D57 leads to the Col de Clémencière (FR-38-0622), in 5 km, from where there are two possibilities:

• 4 km to the Col de Vence via the D57f. Total distance 17.5 km
• or, continuing on the D57, a short descent (1.5 km) leads to the junction (561 m) with the road from Quaix-en-Chartreuse. The road then climbs 6.5 km to Sarcenas (1080 m). From Sarcenas, there is a further 1 km to the Col de Palaquit. Total distance 16.8 km.

North side

If you are coming from Saint-Pierre-de-Chartreuse on the D512 (9.5 km - 900 m along the north-south trough of the massif), you must first descend to La Diat (8.2 km - 794 m), where the climb begins after crossing the Guiers. At 7.4 km from the pass (811 m), turn left onto the D57b (towards Saint-Hugues-de-Chartreuse and the Col du Coq (FR-38-1434). At 4.6 km from the pass (982 m), there is a new junction with the D57b towards Saint-Hugues.
From Saint-Laurent-du-Pont (18 km from the pass - 415 m), head up the Guiers Mort valley for 1 km to reach the D512 at La Diat.
From Saint-Hugues-de-Chartreuse (at the foot of the Col du Coq), 7.8 km from the Col de Porte - 899 m, take the D57b through the hamlet of Cherlieu (5.8 km - 946 m) before joining the D512 (4.6 km from the Col - 982 m).

Administrative status

The Col de Porte is located in the commune of Sarcenas. The boundary with the commune of Saint-Pierre-de-Chartreuse is 800 m to the north of the pass.

What to see - tourism

South side

• Grenoble

North side

• Grande Chartreuse monastery website (the monastery cannot be visited) and Grande Chartreuse museum. Access from the Guiers valley via the D103 (Route du Désert), 1.5 km downstream of La Diat.
• The church of Saint-Hugues-de-Chartreuse houses the Arcabas museum in Chartreuse dedicated to the artist's work (111 works of contemporary sacred art).

At the pass

Ski

• Situated at an altitude of between 1200 and 1650 metres, the Col de Porte ski area has 3 kilometres of ski runs served by 5 ski lifts.
• The Nordic ski area has 3 runs: 1 green, 1 blue and 1 red. 15 kilometres of pistes.

The Col de Porte is a good starting point:

• Direct ascent of Chamechaude, the highest point in the Chartreuse massif, and La Pinéa.
• Because of its topography, the Chartreuse is an isolated massif, and Chamechaude is the 3^e the most prominent peak in the French Alps after Mont Blanc and the Barre des Écrins, with a 1,771 m vertical drop from the Marches threshold (311 m)!
• Route du Charmant Som (built between 1932 and 1937). At the end of the road: chalet, inn and cheese dairy.

Cycling and cycle tourism

Until 2009, the Union Sportive de Saint-Égrève (Cyclotourisme section) - USSE organised the
BRC (Brevet de randonneur de Chartreuse).
This brevet was organised in the opposite direction for each edition. For the version shown in the profile below, the route began in Nord-Isère and Savoie (with the cols de la Placette, des Mille Martyrs, de Banchet and de l'Épine), followed by a north-south crossing of the Chartreuse massif with the col du Granier, the col du Cucheron and the col de Porte, and on the way down the col de Palaquit.
The Col de Porte was therefore on the programme at the start of the race from Saint-Égrève and Quaix-en-Chartreuse or at the very end of the route from Saint-Pierre-de-Chartreuse.
For many «regional» cyclotourists, this brevet was seen as a good preparation for the BRA.

From 2015 to 2017, the Voiron club organised the Brevet de Randonneur Voiron-Chartreuse

Profile

For the «classic» 15km climb from Grenoble (La Tronche), the most difficult sections are at Corenc (south-facing slope).

From the north, from La Diat (8 km), the start is fairly easy, but the road straightens out as you enter the forest after the crossroads with Cherlieu and Saint-Hugues.