Updated 13 February 1998; 19th Febrary 1999; 2nd May 1999; 5th November 2005; 14th May 2006; 6th May, 27th October 2007; 31st May 2012; 25th May 2021; 24th September 2024

The water found in Cueva de Carcavuezo (81), Cueva Llueva (114), Cueva Hoyuca (107) and part of Cueva de Riaño 1 (105) - the Four Valleys System (line survey)- resurges in the Secadura valley. In wet weather the water emerges from a number of openings along a 200m long front but in normal conditions the water resurges at Los Boyones. Major building and piping works were started in the mid nineties and an elevated walkway now passes the "resurgence front"  ending over the main resurgence pool where water is extracted and past over the hill to Moncallian. Trees surrounding the resurgence pool and visible in a 1999 photo had gone by 2006. The treatment works is gated but, if locked, the gate can be easily climbed around. However, a visit in August 2024 mentioned that there could be a security camera beyond the gate and provided a photo showing the chain fence.
The GPS for the extraction pipe is ETRS89: 30T 455713 4799308.

Information gleaned from the Dirección General de Obras Hidráulicas y Ciclo Integral del Agua in 2005 shows an average water flow from the resurgence over the previous 20 or so years of 650 litres per second. (The Fuente Aguanaz resurgence emits 951 litres per second on average. Unlike the 4 Valleys System, there are currently no known feeders or caves which drain to the Nacimiento de Aguanaz). At Easter 2006, an optical brightener test was carried out from the end of the Sumidero de Cobadal. A positive result was obtained at Fuente Aguanaz after a week and with no sign of optical brightener at this resurgence over a full fortnight. A paper detailing the methods, etc can be read here.

The small, excavated cave entrance is 5m above the normal resurgence and located just behind a large embankment of boulders which form part of the pumping station complex. The hole usually emits a strong draught.

A 5m pitch leads to a hole down into the boulder choke (which is unstable in places). The draught can then be followed between the boulders to the river at the base of a steep mud slope.

Various climbs at the top of the slope close down and the draught is lost.

In 1997 a pool of standing water leads to a way on upstream with deep water - not pushed.

Nearby, to the west, is Cueva 77A (site 154) which is all part of the difficult to explore resurgence complex.

Standing at the Los Boyones and looking northwest across the valley, you can see the hillside under which Gour Inlet in Cueva Hoyuca starts. Water in this passage heads southwest to drop into Hoyuca, joining the main flow to pass through Cueva Llueva and resurge on the southern side of Secadura valley.

References: anon., 1974b (logbook); Kendal Caving Club and Manchester University Speleological Society, 1975; Cope J et al, 1976; anon., 1977b (logbook); Corrin J et al, 1978; Manchester University Speleological Society, 1982; Mills L D J and Waltham A C, 1981 (survey); Corrin J S and Smith P, 1981; anon., 1981a (logbook); material in file; anon., 1989 (logbook); Corrin J, 1992b (survey); Corrin J, 1994b (survey); anon., 1996a (Easter logbook); Corrin Juan, 1997a; Corrin Juan, 1997b; anon., 1997b (logbook); Corrin Juan, 1997c; anon., 2005c (autumn logbook); Corrin Juan, 2006a; anon., 2006b (Easter logbook); Corrin Juan, 2007; Corrin Juan and Smith Peter, 2007; Corrin Juan, 2013a; anon., 2024d (summer logbook)
Entrance pictures : yes, dye tracing : gate and fence, 2024
Underground picture(s):
Video: Retrieving a cotton wool detector during high water flow. (Phil Papard)
Detailed Survey :
Line Survey :
On area survey :
Survex file : yes (Amended magnetic declination December 2013 to align with Eur79 grid and coordinates altered to fit ETRS89 datum, April 2014.)