Dent de Crolles is the high point of an extensive upland massif in the Chartreuse hills of the French Prealps. Its summit of 2,026 metres dominates the Grésivaudan valley to the south, whilst to the north a tilted synclinal plateau, protected by high cliffs on the west and east, descends for 1½ km to the edge of a cliff-encircled cirque overlooking the Perquelin valley, some 3 km ESE of St. Pierre de Chartreuse. To the south-west of the summit, a road ascends to 1,434 m at the Col du Coq allowing easy access to the plateau along the waymarked GR9 footpath. The hill owes its name to its resemblance to a giant molar when seen from the village of Crolles in the valley below.
Mesozoic in age, Dent de Crolles is capped by Urgonian limestones deposited during the Aptian and Berremian stages of the Early Cretaceous (c. 129 Ma - 120 Ma), overlaying impervious Hauterivian marls. The limestones are honeycombed by an extensive cave system, the Réseau de la Dent de Crolles. This has over 60 km of interconnected passages contained within an area of under 2 km² - one of the highest ratios of cave passage to bedrock in the world; and thirteen entrances including the resurgence, and a top entrance located under 200 m from the summit.
The system consists of a number of active passages fed by autogenic recharge that flow into a master cave, and a labyrinth of far older large fossil multi-level phreatic passages formed from the early Pliocene (circa 4.5 Ma) onwards which drained landscapes long disappeared (See note). These were truncated during the Quaternary glaciations, and now have large entrances overlooking deep valleys in the north, east, south, and west cliffs of the massif. The fossil passages have been intercepted by the active passages to create a vast network, the plan survey of which has been likened to a plate of spaghetti. Although the limestone beds are only about 450 metres thick, the local geological structures means that the system is only a little shy of 700 metres deep.
The Réseau de la Dent de Crolles provides perfect holiday caving in a beautiful area, with a large number of classic through-trips and round-trips available of varying degrees of difficulty, as well as providing scope for more challenging expedition-style caving. It is possible to traverse from the top of the mountain to near its base, and through the mountain from one side to the other, and combinations of the two. Several of the more popular routes are waymarked and superbly equipped with pull-through chains and traverse lines. Some of the through-trips take around 4 hours, and others over 12 hours. All the entrances are reasonably accessible with the walk-ins varying between about ¾ of an hour, and two hours.
The purpose of this website is to pull together the latest pertinent information on the cave, and to clarify the locations of the entrances. Please look at the Sources of information page for a summary of available material, much of it on the web.
As of June 2021 the following 13 entrances, ordered by altitude, are known. Entrances with hyperlinked names are discussed further on this site. The locations can seen displayed on the IGN Géoportail aerial photography website, on a map created by Gilbert Bohec. The entrances are shared between three communes, all in the département de l'Isère - St. Pierre de Chartreuse to the north; St. Pancrasse to the south; and St. Hilaire to the east.
|Gouffre Bob Vouay 3||45.30960°||5.85445°||2,022 m||St. P. de Ch.||2009||190 m from and 40 m below the summit
Links with Trou du Glaz and Grotte Chevalier
|Gouffre des Quanta 4||45.31679°||5.86455°||1,937 m||St. Hilaire||2001||About 160 m south of Gouffre Thérèse
Links with Grotte du Guiers Mort
Accessed by a 50 m abseil down the eastern cliffs
|P40 1||45.31259°||5.85357°||1,930 m||St. P. de Ch.||1947||Equipped route to Trou du Glaz|
|Gouffre Thérèse 1||45.31821°||5.86458°||1,925 m||St. P. de Ch.||1975||Equipped route to Grotte du Guiers Mort|
|le Nid de Choucas 4||45.3089°||5.8571°||1,864 m||St. Hilaire||2021||Discovered from below by scaling in the Grotte Chevalier.
Entrance high on the eastern face
|Gouffre de la Pulpite Irréversible 3||45.31407°||5.85586°||1,901 m||St. P. de Ch.||2010||Equipped route to Trou du Glaz.
Also links with Grotte du Guiers Mort
|Puits des Cartusiens 2||45.32081°||5.86179°||1,780 m||St. P. de Ch.||2007||Links with Grotte du Guiers Mort|
|Grotte des Montagnards 4||45.3096°||5.8585°||1,717 m||St. Hilaire||1966||Entered and linked with Grotte Chevalier in 1966
Accessed by an 80 m hard rock climb on the eastern face
|Trou du Glaz 2||45.31736°||5.85146°||1,697 m||St. P. de Ch.||----||Equipped routes to Guiers Mort, Annette and Chevalier
Exit for equipped routes from P40 and Gouffre Pulpite
Equipped round trip
Link with Gouffre Bob Vouay
|Grotte Annette Bouchacourt 4||45.30599°||5.85375°||1,685 m||St. Pancrasse||1946||Exit for equipped route from Trou du Glaz|
|Grotte Chevalier 4||45.307°||5.85468°||1,670 m||St. Pancrasse||1984||Exit for equipped route from Trou du Glaz
Links with Bob Vouay and Grotte des Montagnards
|Maxi Méga Marmotte 4||45.307018°||5.8553°||1,649 m||St. Pancrasse||2020||Alternative entrance/exit into/from Grotte Chevalier
(See Grotte Chevalier for more details)
|Grotte du Guiers Mort 4||45.32611°||5.85757°||1,332 m||St. P. de Ch.||1941||Exit for equipped routes from Trou du Glaz and Thérèse
Also links with Gouffres Quanta, Cartusiens, and Pulpite
Two equipped round trips
1 Location from Spéléo Secours Isère route guide
2 Location from Gilbert Bohec's survey
3 Location from author's GPS reading
4 Location supplied by Gilbert Bohec
The following files are available for importing entrance location details:
- Reseau de la Dent de Crolles.gpx - for importing into GPS and Memory-Map etc. (5.0 kB)
- Reseau de la Dent de Crolles.kmz - for importing into Google Earth (1.7 MB).
In addition to the caving, the area also offers magnificent walking, as well as ample opportunities for big route climbing, sport climbing, canyoning, and via ferratas. For more information on the area consult the author's Chartreuse website.
You may download a PDF copy of this website.
I would like to thank Gilbert Bohec, Dagobert L'Ecluse, and Glenn Jones for their help and advice given during the development of this website; Dave Checkley, Graham Coates, Stuart Heseltine and Pete Monk for their kind permission to use their photographs; and the various authors and organisations who have generously shared the results of their expertise on the Web. Errors and omissions are all mine.
The late Miocene date has been extrapolated from work done on the age of sediments in the caves of Mont Granier. See: Hobléa, Fabien & Häuselmann, Philipp & Kubik, Peter. (2011). Cosmogenic nuclide dating of cave deposits of Mount Granier (Hauts de Chartreuse Nature Reserve, France): morphogenic and palaeogeographical implications Géomorphologie : relief, processus, environnement. 395-406.