Thunder Canyon was the first of the impressive Carmarthen canyons to be discovered. It was first descended in 1960 by an SUBW party of Colin Oloman, Gerry O'Byrne and Dick Donaghey, as part of a trip from Mt Charles on the Bell Road to Leura. The discovery gave a major boost to the exploration of sandstone canyons in the Blue Mountains.
Thunder Canyon tends to be overshadowed by its tributaries Claustral and Ranon as access is more difficult, and the best part of the canyon can be visited from the bottom.
The NPWS requests that canyoners use the exit route as described for Claustral Canyon, and not to form new tracks. When returning from the Camels Hump use the old track across the Camels Saddle to the minor saddle, and down into Claustral Brook. The notes below describe this route. The exit is also shown roughly on a map. It is recommended that canyoners have previously entered Claustral via the new route before attempting to use it as an exit for Thunder.
Leave a car at the Claustral car park at MGA583847 just past Mt Bell. Walk (or drive) 2.5km west along Bells Line of Rd to Mt Charles. If you are driving, there is an open area on the right hand side just after the top of the hill to park at, though visibility is poor. A better option may be to park earlier on the at MGA568845, near the 888 point, where the visibility is better. Either way, walk to Mt Charles.
Navigate carefully along Lightning Ridge to near the end where it starts to drop steeply. Make your way down to the south and east to a significant cliffline. Entry into the creek will usually require one or two abseils, up to 25m - some scouting around may be needed to find appropriate spots, as the cliff is quite high in places. Around MGA585825 there is a ramp that may get you fairly close to the creek. Otherwise near the southern point.
A better approach may be to enter the creek higher up, around the creek junction at MGA577830. This avoids some of the scrub on the ridge, but may still require an abseil, and adds a kilometre of creek walking. It also allows the first canyon section mentioned below to be passed through.
The main canyon section starts downstream at MGA586825. There are a few options for the abseils. A good option is 20m from a tree down the falls to the left, and then 8m down the next section. The first person should check that the crack to the right is not blocked before pulling ropes. Alternatively scramble down the gully to the right (rope may be needed) and do about 20m from a tree.
There is a superb section of high narrow canyon from here to the Claustral junction, about 300m long.
The creek opens out for about 500m before narrowing again. There are some tricky climb downs in the next section. There are also two longer drops of about 5m each, which usually have fixed ropes in place. The first one of these is just before the Tunnel Swim, and many parties would be advised to abseil this. The second is easier, but is dangerous in high water, and should be abseiled on the right hand side in those conditions. In between the climb downs is the Tunnel Swim, which can sometimes be a wade, but is usually a long cold swim up to 50m through a dark tunnel.
About 50m past the second climb down, Rainbow Ravine is a reasonably obvious sloping waterfall that comes in on your left, as the creek bends right. A further 50m past this there is a final 20m swim to the exit gully. Many parties miss this exit and end up being benighted in the canyon, so be careful.
Scramble up the exit gully for about 20m and then traverse left under the cliff to Rainbow Ravine. Head up Rainbow Ravine. There are a few tricky scrambles, and some wades (for those who carry dry socks or shoes).
Where the gully splits higher up, head up the left branch. At the top there is a small waterfall, involving two tricky scrambles. It is easier (and quicker for most parties) to avoid these scrambles by walking to the right along the ledge to the other gully, and then up a ramp and back over the top. This avoids further erosion in the already eroded gully above the waterfall. Otherwise, scramble up the waterfall. The first is up a log braced with rope. The second can be made easier by stepping to the right and using the side of a good handhold for the left hand.
From there follow the obvious track up to the Camels Hump. Head down and right to the Camels Saddle, ignoring tracks off to the left, and then up a short way to the next minor saddle at MGA597834. Turn left here, and follow the track steeply downhill until you reach Claustral Brook.
A track can be followed alongside the creek for some way. Continue downstream past the junction with Dismal Dingle. There are a couple of canyon sections in here. There are two deep wades or short swims shortly before you reach the exit gully on the right at MGA589837.
Scramble up this gully and try and pick up a track that leads NNW back to the road at the sharp corner at MGA585846. Walk back along the road to your car.