Dent de Crolles - Cirque Sans Nom
Starting point: Perquelin Difficulty: 3 Ascent: 730 m Time: 5½ hrs Quality: **
Anyone who has spent much time on Dent de Crolles cannot fail but be intrigued by the large cirque into which the plateau's synclinal basin plunges. It looks as if a large mouthful, some 500 metres long and 350 metres across, has been chomped out of the hill, the north walls of which are topped by Le Prayet, and the south by the Belvédère. Its overall architecture is probably best appreciated from La Scia, but the finest views into it are from the GR9 as it approaches the Cheminée du Paradis cliffs. Here one can appreciate the size and seeming impenetrability of the place. However, there is a route into it from the bottom, which manages to exit in the north-east corner. It traverses pathless terrain, and includes three awkward scrambles, and for that reason it deserves its grading. It is a must for Chartreuse aficionados, but is probably best left alone by the less frequent visitor. The route only scratches the northern side of the cirque, but it does allow access to the rest if you want to explore further. This particular walk descends from Le Prayet (see map) down the Sentier du Colonel, but it could equally descend via the Sangle d'Arche et Aiguille.
The Perquelin valley is a narrow valley that runs south-east from St. Pierre de Chartreuse for about three kilometres to the hamlet of Perquelin. Drive to the top of the road, and at its conclusion, continue along the forest track for 100 metres, where you will find a car park (990 m grid ref. UTM 31T 72314 50237. Our first target is to find the entrance to the Guiers Mort cave.
From the car park follow the forest track past a clearing, until you cross the Guiers Mort stream, and also get a glimpse of its waterfall above. Immediately on the other side of the bridge, a path ascends pleasantly through the woods, passing the Fontaine Noire - a captured water source which is the resurgence for the Chaos of Bellefont area above.
Continue on the path uphill for a few minutes, then take the next junction to the right, which soon leads to a forest track. Turn right, and after 100 metres, turn left just before the Guiers Mort stream, some 10 minutes after leaving the Fontaine Noire. This path rises through the forest, until it descends to a set of metal "stepping stones" across the stream, with the imposing cave entrance (1310 m) above. You, however, carry on towards the cave entrance.
A path heads up the hill some twenty metres before the cables leading up into the entrance start. Take this, and follow it north under the cliffs. A small cave entrance is passed after a few minutes. The path then becomes lost under a mass of dead leaves and fallen branches, but some five minutes or so from the cave the angle of the cliff eases, and it is possible to scramble up (slippery when wet). Once at the top, trend generally half-left, and with a bit of luck a couple of cairns and thin trails will lead onto some scree below the northern flanks of the cirque. Here a thin path make an ascending traverse of the scree slopes. Some 30 minutes after leaving the scramble, a steep grassy slope is encountered which is ascended for ten minutes to an awkward 3 metre scramble. Above this is a sweep of cliffs topped by a large overhanging promontory on the left. This is a good place for a second breakfast with a fine view of the Perquelin valley, although we had to retreat rapidly from this point when a herd of chamois started kicking stones down from the cliffs above.
From here make for the path that traverses scree below the cliffs, and then wend your way up a loose ascent into an upper cirque. At the top, about 20 metres from the left hand side of the cirque, there is a weakness in the cliff marked by a gnarled tree. It is possible to climb up here - alternatively there is a recess in the cliff a few metres to the right where a short climb onto a sloping ledge allows an even easier ascent. Above this a path leads directly to the GR9 and civilisation within 5 minutes.
The cliffs descending from the Cheminée du Paradis are immediately in front, and the GR9 follows a pleasant rake through them, and then traverses a steep bit of prairie. After a further 15 minutes you reach le Prayet, a flat meadow area with a well decorated tree. The GR9 continues to the north, and we turn left towards the cirque down the Sentier du Colonel.
Apart from a couple of short steep gullies, this is a superb descent path, which makes its way easily back down. After an hour's descent, you meet a forest track - cross this to a continuation of the path. After another five minutes, turn right at a T-Junction and you will find yourself back at the Fontaine Noire from whence you can retrace your ascent route back to the car.