Georges and I climbed the Petit Tas passage up from the east side to the Chartreuse plateau on a weekday, then hiked to the summit of the Dome de Bellefont. My first time on the pretty east Chartreuse ridge in the summer, an engaging challenge, and a fine day out.
There are three requirements for doing this: (1) find the Petit Tas trail; (2) hike up some pretty steep trail; (3) climb the Petit Tas. Starting with the first, here’s some possible help with GPS navigation. Since much of this was under trees and near cliffs, locations from my GPS are not always accurate.
* road junction for La Batie: latitude/longitude = (N45.34424 E5.90547)
. . . seemed like only one or two legal parking spaces on the narrow road west up from this
junction toward the trailhead—so be prepared to look for parking elsewhere.
* trailhead La Batie = (N45.34637 E5.90457)
. . . trail starts roughly due west from la Batie
* junction with trail up from les Guillots = (N45.34734 E5.89700)
. . . (the trail up from la Batie was much nicer than the one from les Guillots, especially on descent—glad for David’s suggestion of this)
* junction of trails—sign “sous les Charassons, 1330m” = (N45.35093 E5.89744)
. . . trail going left from junction was a normal-width forest road (not narrow). Road has puddles and mud for several days after significant rain.
* water tank ("reservoir") = (N45.34914 E5.89121)
* start of trail for Pas des Charassons = I didn’t capture GPS latitude/longitude. It’s somewhere between the water tank and the start of trail for Petit Tas.
. . . We missed it on first pass. There was no cairn any more. It starts angled right away from forest road, so it’s easier to see going north. So if miss it at first going south, try again going north.
* start of trail for Petit Tas = (N45.34719 E5.89007)
. . . pretty steep, slippery when wet. Very difficult until it dries out after rain—and it doesn’t dry out fast because it’s sheltered under big trees. Trail starts going West.
* trail turns North (near scree) = (N45.34711 E5.88684)
* trail reaches ledge = (N45.34862 E5.88600)
. . . follow ledge north + east
* Petit Tas - bottom (GPS reading inaccurate because of cliffs) = (N45.34932 E5.88715)
. . . We had a 45-50 meter rope, so I led most of it to a belay just above the big pine tree with rope hanging from it—which produced substantial rope drag after passing a smaller pine tree (? diameter 15cm ?) about mid-way. Perhaps if had stopped and belayed from that smaller pine tree, might have had less rope drag later. Anyway Georges took over above the belay and led to the top. The upper section had like 10m on nice rock, unlike much of the rest with significant vegetation.
. . . I’m not that esperienced with French technical climb ratings, but felt to me like at least difficulty 3, or more like 4 with the weight of full day-pack and the rope drag.
. . . The protection I placed was mostly quick-draws ("dégaines") clipped to the artificial cable anchor points or rope knots; or slings ("sangles") wrapped around trees. But for extra protection, I placed a medium/large Friend and a medium/large stopper ("coinceur")—small stuff didn’t seem useful. Perhaps other people would have found the Friend and/or stopper unnecessary, and just relied on the quick-draws and/or slings.
* Petit Tas - top (approx) = (N45.34946 E5.88705)
We found a nice lunch spot just over the top.
After this we joined the GR9 trail SSW to the Col de Bellefont, then climbed the Dome de Bellefont.
. . . A more interesting way to the summit of the Dome de Bellefont might have been to go to the east side of the NNE ridge of the Dome, then climb SSW to the summit of the Dome. But we’ve heard this has a very steep section, and we didn’t know the best place to cross to the east side. For more info about this option, see the guidebook: Chartreuse Inédite, by Pascal Sombardier (Glénat 2006).
Then we descended west, and followed the GR9 trail north to ...
* trail junction GR9 with Aup du Seuil access = (N45.35571 E5.88390)
. . . another alternative would have been to cross at the Pas des Charassons, but we weren’t sure how to find it from the top, or what it might be like in the downhill direction.
* trail crosses of ridge by Aup du Seuil at = (N45.35816 E5.89684)
Then we descended the trail back to la Batie.