3917: SixFourOne, Cueva
Riaño 30T 452346 4800064 (Datum: ETRS89. Accuracy code: A) Altitude 262m
Length 50m Depth 10m
Area position

Updated 26th March; 13th October 2014; 5th January 2015; 8th January 2018

   Site 3917 (east) is a prominent entrance with a mature tree growing right outside. A 4m wide, low slot goes down a 5m long earth bank (covered with small sandstone rocks) into walking passage that quickly becomes a narrow rift, generally of walking height, but occasionally requiring crawling. One squeeze has been opened up a little. The passage here is 1m wide and 3m high and the walls are covered with powdery (like icing sugar) formations.
   Forwards leads to either a crawl at floor level or a climb up to route just under the roof. The crawl at floor level can be followed via a squeeze to a very short section of standing passage and an abrupt end to the cave. The high level route terminates at a hole back down into the lower level about 2m from the end of the passage. The end is a circular enlargement just under a metre diameter and about 3m high with wet, mud covered formations. The route is choked with calcite at roof level, with a mild draught through a hole in calcite. Further progress is unlikely at this point.
The main line of development is on 48 degs. The passage is hading under the west wall.
    On an early visit, daylight was noted entering the roof bedding on the west side of the cave. Rather than excavating the bedding in the cave, a few rocks were moved outside to give access to the bedding. At this point a steep slope goes down into a parallel passage running back into the hill. This western entrance leads further back into the hill and is deeper than the initial cave.
   Western entrance
   The hole on the left at the base of entrance slope (requiring a ladder) has been examined and is the deepest part of the known cave but would need digging to get to that point. The descent is a series of squeezes maybe going down 14 or 15m below roof level. This has not been pushed further.
   Moving on in the entrance passage, a T junction is reached with a run in from the left. Going up the right hand side of this run in slope, the sandstone roof steps up where the
bottom part of the sandstone bed has fallen off. Here a bedding runs off to the west to a point where daylight can be seen. On the surface this point is a couple of metres east of the eastern entrance to site 3918. ( It looks as though 3917 and 3918 could be connected by digging under the lowest part of the sandstone bed.) There are now numerous rifts going back into the hill from the bedding, so its possible there may be others off this bedding.
   Turning to the right at the T junction at the end of the entrance passage, the run in slope can be followed down to a point that would need digging to get through. Above here a large crack/slot in the sandstone bed has allowed some impressive stals to form. You can climb up here and traverse forward to a pit about 4m deep to a debris slope. Forward across the pit seems to be blocked by the stal flows, but a way on at the base is being followed in the same direction as the sandstone slot. The pit was laddered off a couple of large columns and the walls are quite loose. (Care! There is a large loose lump of stal column looking like a plaster leg cast at the end of the traverse!).
   A cold, draughting dig is progressing at the base of the pit, where a larger bit of passage was entered for 10m. The current end is now a smaller draughting hole that is still a good dig prospect as there is stacking space.
   At Easter 2014, it was reported that the "muddy dig is too small" and further work is required to enlarge the passage. Work continued in the summer when the tight squeeze into the final passage was removed and capping continued. In November, the site was cleared and opened up to allow access to an open rift passage. This soon closed down and a higher level continuation was also found to close in.

Reference: anon., 2013d (summer logbook); anon., 2014b (Easter logbook); anon., 2014c (summer logbook); anon., 2014d (autumn logbook)
Entrance pictures : western entrance : eastern entrance
Underground pictures : summer 2013 CC : summer 2013 & 14 PPA
Video : capping in 2014
Detailed survey : cave surveyed?
Line Survey :
On area survey :
Survex file :