Leaving Son La town to the south-east, route 69 brings you to the Nam Mua river. The area on the eastern side of this road, between Ban Mat and Ban Cop Men, turned out to be uninteresting from speleological point of view; the caves, located in the base of low karstic towers, are small and fossil, most of them being choked with mud almost to the top. A few kilometres to the south, in the Ban Key-Puon area, close to the karst boundary, we were showed an interesting cave that drains the water to the valley of Ban Cup. Because we investigated this area at the end of our stay, no more caves
were found. However, it seems to be interesting to go back and check the other side-branches of the Nam Mua river.

MS04 Ban Puon

At the end of the valley, close to the sinkhole of the river, 10m above the bottom, the entrance is a small crack. The moistness of the draught is so high that glasses become fogged whilst approaching the entrance. According to different villagers there was a search for gold in the cave many years ago (we indeed found many traces that much energy was used to make the cave accessible and to exploit it). Some children said that they used the cave as a passage to the nearby valley of Ban Cup. After an 8m pitch, in which stood a rotten bamboo ladder, one arrives in a fossil gallery. A little climb leads into a muddy chamber, in which a 4m pitch drops into water which emerges out of the nearby sump. The water becomes deeper; one has to swim about 15m to arrive in a beautiful calcited chamber, where we found an old wooden sieve, a small table with rice-bowls and joss-sticks. A climb over boulders brings you back to the shallow water. The rift widens and gets very high (one cannot see the ceiling). Here and there the river is dammed with wattle-work. Some bamboo piers made us think that a bridge was once built through the wet parts of the cave to keep the gold-diggers out of the water. After passing a dry chamber with huge boulders on the floor, one arrives in a section where the water is again deep and stagnant. Here we found an old knife. The river leads to a lake (10m x 10m) where a narrow passage gives access to another little chamber, which is filled with bamboo. These are probably the remains of a platform, on which a ladder could bring you through a chimney into the higher level of the cave. A little duck gives access to another little chamber, which is choked with mud. The way on probably lies beyond the chimney, but we were unable to climb it. We also explored the emergence in Ban Cup, where the water is captured by a concrete basin. The access to the cave lies 10m above it. A 20m long horizontal part is followed by a pitch which was not descended.