0105: Riaño, Cueva de (Riaño 1, Cueva de) (Reñada, Cueva de la)
Riaño 30T 451780 4800279 (Datum: ETRS89. Accuracy code: G) Altitude 155m
Length Part of the Sistema de Cuatro Valles (Traverse length for the Four Valleys System: see Cueva Hoyuca) Depth 92m
Area position

Updated 19th February , 18th April 1999; 16th September 2000; 7th October, 26th October 2001; 25th October 2002; 1st February, 14th May, 1st October 2006; 15th January; 12th February, 6th May, 28th October 2007; 24th January, 15th April 2008; 4th May, 24th August 2009; 16th January, 8th, 9th March, 24th June, 4th October 2010; 6th January, 12th May, 3rd, 11th October, 30th November; 9th December 2011; 13th January, 18th February 2012; 23rd April, 20th September 2012; 21st April 2013; 19th January 2014; 25th September, 17th October 2015; 14th October, 5th, 30th November 2016; 12th March 2018; 1st May, 1st July 2018

Incomplete description

The most northerly entrance into the Four Valleys System (line survey). A route through into Cueva de la Hoyuca (107) exists - and ultimately to Cueva Llueva (114) and Cueva de Carcavuezo (81). The depth is taken to the downstream sump in Cueva Llueva. The resurgence (site 575) for water flowing west in the cave (rather than east into Cueva Hoyuca) was dived and connected through to downstream Cueva Riaño in July 2016. A detailed survey can be found here.

Entrance Series

The strongly draughting entrance lies in a tree lined depression next to the track. The passage starts low - it often has to be dug out - and passes an earth run-in on the left. The entrance was dug out again during the Easter 2006 expedition, and a barricade built using an abandoned domestic oven and some rocks to attempt to stop mud being washed in again. After the short flat out section the going becomes easier with hands and knees crawling. After 50m a small inlet is met from the right and the way on follows this water and gradually increases in size. Several side passages are passed which are mostly oxbows but can cause confusion on the way out (follow the draft on the return if unsure which way to go). The streamway passes a small inlet on the left with gour pools, then continues as a mix of stooping and crawling for around 150m until it breaks out into an area with boulders and larger cross rifts up in the roof (unsurveyed). Continue following the passage at floor level to regain the stream and follow until some 250m from the entrance the stooping passage breaks out into a second larger area with holes in the roof. At this point it is possible to climb up directly back over the top of the passage you came along to gain a small dry sandy passage which leads to Double Barrel Passage via Grey Rock Chamber and is the best route to the upstream parts of the cave. Continuing straight ahead however leads within 20m to a 7m pitch reached via a slot down on the left. The pitch can be free climbed by traversing over the drop (after descending the slot) and climbing down on the far wall. Before the slot leading to the head of the pitch it is possible to clamber over a mud bank in the main passage to reach a larger ascending passage which eventually chokes. A few metres downstream from the base of the pitch the main stream is met and the passage size increases at Eureka Junction.
At the "first boulders in the entrance stream where you climb up" (about 130m in), an extension was dug into at Easter 2009, this has a good draught and a number of intersecting passages. Shown as "HSC" on the 0105.3d file.
Further surveying of new passage was carried out in the entrance series in February 2010, adding 349m. Lots of egg shells were seen in the extension. The first way up into it is near the entrance on the bend where you can first stand (stoop) along, just before the gour pool inlet is reached, only about 5 minutes in. There is a visual connection with the HSC series. The largest passages are a few metres wide, but all flat-out bedding planes. There is lots of calcite on the floors and blocking some passages below which certainly used to connect. (One passage from stuff nearest the entrance ends at a complete calcite blockage not far from the larger bedding plane passage). The end of the bedding plane passage nearest to Grey Boulder Chamber is too low, dig-able, but still a long way from Grey Boulder Chamber itself. The other end is heading towards Mad Axe Woman cave. A survey of the Entrance Series and passages off, can be seen here.

Downstream Riaño

Downstream the passage is 2m wide and 4m high and runs for 100m past some stalactites to a 1m cascade and a bend to the right, followed by more free climbable cascades of 2m and 3m. The last of these is the most awkward climb. The passage then turns left, and continues along a rift to a short section where you are forced to crawl in the water under some low hanging formations. This is followed by another bend to the right, leading to a pitch of 4m with a large pool at the base. At the head of this pitch an easy traverse gains a large dry phreatic tunnel which immediately turns left, with a smaller rift passage leading off right on the bend. (The large dry phreatic passage has been surveyed but no description has been found. I think the Ghost Rift series is somewhere in this area - Footleg. This was partially surveyed at Easter 2013 [and completed 1/8/2015? JSC]. Also surveyed was a steeply ascending oxbow with avens which emerges high in the roof of the streamway above the pitch at the Torno Inlet junction.) The smaller rift leads to an easy 4m free climb down to gain the floor of the active Torno Inlet. Downstream this inlet immediately flows under a low wet arch which can be bypassed via a short muddy moonmilk tube to emerge at the pool below the 4m pitch back in the main stream. The water from the inlet enters from under the wall here.

Downstream from the base of the 4m pitch the stream runs off to the left and the passage lowers to a crawl. This does not last long and after a further 200m of easy going, another pitch of 8m is met with an awkward crawl at the bottom. (At the foot of this pitch the survey data indicates a climb back up to the same level as the pitch head, and a continuation which rejoins the stream further down). The cave sumps 200m from this point and is then some 500m from its resurgence (575). Some higher level passages lead off from this lower downstream section on the line survey (see 'Grov Write up' section at the end of this description). In 2012, the resurgence was dived for 207m, continued at about -2m, and was finally joined to the main cave on 15th July 2016 by Jim Lister. See site 575 for details.

Torno Inlet

Following the inlet upstream the passage ascends a 1.5m step up followed by a couple of bends to a decorated corner where formations prevent progress at roof level, forcing you through a short wet grovel at stream level. The going becomes easier beyond as the stream is followed in a tall narrow rift until the passage develops into a wider phreatic section with the stream in a floor trench offset from the passage above. A short section of wider gravel floored passage follows leading to a 90 degree bend to the right immediately followed by a 90 bend to the left. After these bends the passage develops into a tall narrow canyon providing relatively easy going for the next 125m to another prominent 'S' bend where the stream undercuts the right wall. This marks the start of the crabwalk, about 275m long (but feels much longer!). About half way along some helicites can be seen on the left wall, and a little further on a pinch at a calcite curtain has to be passed. A brief respite is met at an aven with a small active calcite flow down the left wall. An easy climb up to the roof here reveals the inlet to enter from an impenetrable hole, but the main passage at this level is a 3m diameter phreatic tunnel with the crabwalk trench in the floor. A side passage enters at this point, but quickly degenerates to a flat out descending mud slope where it becomes too low. Two flat out squeezes have been passed here, and roomier space can be seen beyond a third squeeze. The floor needs digging out to make these passable.

Back in the main passage it is possible to head back in the downstream direction at roof level via easy traversing on mud ledges, passing a second phreatic side passage on the right hand side (facing downstream). This has been followed to a junction where the left leads to a mud choke, and right leads to the base of an unclimbed 10m aven. Back in the main passage it is possible to continue the downstream traverse for a long way until the mud ledges become more precarious and sections of flat out crawling are required. It is a long way down to the stream here and a difficult down climb, so not recommended as an alternative to the crabwalk below. No further side passage have been found here.

Back at the bottom of the active calcite flow in the streamway the crabwalk continues upstream until the passage is blocked at stream level by some large slabs. The way on continues at roof level over these until the trench in the floor disappears and the passage becomes a wider stooping height bedding which soon lowers to a bedding crawl. This is followed until the roof rises and the passage becomes a narrow rift again at an area of formations. Shortly beyond this point the passage becomes a bedding crawl again and the stream emerges from a sump just beyond. Back at the area of formations a strong draught can be felt coming out of a narrow hole on the right at floor level (when facing upstream), with a wider passage seen beyond. This passage can be entered by climbing up to roof level and through a larger hole. An aven is reached after 4m which was climbed in December 2006 and made passable at the top. This is now rigged as a 10m pitch which is quite tight at the top (photo: Paul Dold) and breaks out into a 2m diameter phreatic passage above (the Road to Torno extensions).

At Easter 2013, a trip into Torno Inlet surveyed high level rifts, shown as "tornolinkpush" in the 3d file. One opinion of the pushing trip that carried out the survey: "Long trip that was abandoned by myself and 4 members of the 6 person team. It requires a much more considered approach and ... the cave is pushed by those with the necessary head for heights or that tackle is taken in to aid progress."

The Road to Torno

At the top of the aven at the end of Torno Inlet, a phreatic passage can be followed in two directions. One direction (due South) has a narrow stream trench in the floor, the other direction heads back over the top of the Torno Inlet passage (heading NW), crawling on a mud covered white crystal floor which is revealed when bits of mud stick to your knees and pull off the floor. After about 40m this breaks out into a larger phreatic passage at a T-junction. To the left the larger passage continues as a flat out crawl on flowstone. To the right the flowstone fills half the passage height apart from a trench along the right hand wall. To protect formations in the trench it is best to crawl along on the higher flowstone floor. Some fine curled up flakes of cracked mud are passed with care on a left hand bend, then the trench swaps sides a couple of times and has to be crossed over and back again to stay on the higher floor. A second T-junction is reached, where left leads via an unsurveyed oxbow to a window overlooking a chamber. Going right at the junction a squeeze past a flowstone bank is met. This looks deceptively larger than it actually is! After the squeeze you are forced to traverse over the trench in the floor, which contains delicate looking calcite slabs. The traverse ends at a 4m climb down alongside a fine thin calcite column (the Hypodermic Lance), to gain the floor of a chamber where the oxbow passage already described enters at a window 4m up the left hand wall. The far end of the chamber is reached by carefully crawling between two long straws. A flat out squeeze under the left wall leads to a parallel smaller chamber with more formations. The roof slopes down to the mud floor at the end of this chamber, at a point located at the same height and about 20m from the too low end of the roof passage above the aven with the calcite flow in the Torno Inlet streamway.

Back at the top of the aven near the end of the Torno Inlet, the passage heading due South leads quickly to a T junction. Right follows the stream trench along a much narrower passage which meanders for 25m to a second junction. The stream trench here comes from the right hand branch, and is about 3m deep but only 6 inches wide. Both passages beyond this point have not been pushed to a conclusion, but continue as sideways crawling around many bends.

Back in the main passage, going left at the junction leads to another T junction where it meets a tall rift passage. Right leads immediately to the bottom of a 15m high aven. The passage continues past the aven to a 2m climb up. Above the climb a bend left follows, leading to another T-junction. Right at this junction is unexplored. Left follows a tall rift, traversing part way up. A passage is passed on the right which leads to a ledge half way up to 15m aven below the 2m climb. The traverse along the rift continues past flowstone and curtains which have been cracked (presumably by seismic activity) until after 60m it is possible to climb down into an active streamway. The passage widens to 3-4m at roof level with many formations around this area. Upstream leads to a steep slope with large blocks. A large ammonite fossil is seen on the right here on a boulder. At the top of the slope the stream emerges from a boulder choke of large sandstone blocks. It is possible to climb up to the roof here and a possible bolt route was inspected on a trip at Easter 2011. Downstream in the rift a short section of fine sloping streamway leads to a waterfall which can also be reached from below via another route.

Heading left at the junction just before the 15m aven, the passage passes under a large slab wedged in the rift to an easy climb down into a larger rift. This can be followed in both directions to reach the same chamber. Right passes fine mud drill holes in the floor. Alternatively left passes a short section of passage on the left which chokes, followed by a short crawl on mud. Both routes reunite in a chamber where the waterfall enters from above. It is possible to reach the top of the waterfall via an exposed traverse. At the far end of the chamber the water flows round a right hand bend along the floor of a section of passage with a fine phreatic tube containing stalactites and straws above a vadose trench. At the end the phreatic tube finishes at a circular hole where you drop down into a lower space with stalagmite columns all round (The Jail). The stream flows right and then back on itself to run parallel to the passage just followed. Squeezing through the bars of the jail leads to a flat out crawl on boulders to a sump. The stream flows into this sump in the direction of the upstream sump in Torno Inlet, which is located about 25m away on the same level.

Over 600m of extensions, including large, high level tunnel, were entered over Easter 2007. Full description and survey are to come.

Grey Boulder Chamber and The Mazeway

Climbing up into the dry sandy passage in the entrance series shortly before the pitch, the passage heads directly back over the entrance streamway for a short distance before a 90 degree bend to the left. The first maze like area is then entered, but most of the passages either form loops back onto each other or quickly choke, so it is easy to find the way through. A long straight section of passage is then followed past several cross rifts to a 90 degree bend left. After the bend the main route is generally straight ahead and then trending slightly left to emerge in Grey Boulder Chamber. This is in fact one end of a high rift with large boulders strewn around. The route through to Double Barrel Passage goes more or less in a direct straight line in the direction you are going when you entered the chamber. Zig zag left around boulders, then climb up about 1.5m onto the large grey boulder and continue in the direction you were going, leaving the chamber via a rift passage which leads to the complicated junction at the start of Double Barrel Passage after 20m.

At the end of March 2018, the Grey Rift extension, heading north from Grey Boulder Chamber was surveyed. (Batch greyriftnorthextn length 121m)

The large rift which starts at the grey boulder can be followed for about 100m past high avens (unclimbed) via a number of routes around boulders to a junction where a narrow rift heads left and leads into the Mazeway, a very complicated set of narrow dry muddy rifts which total some 500m in length. Through this maze an inlet streamway is reached. Upstream the passage increases in size and after 150m reaches a draughting choke which appears to be only 40m from the surface. This inlet passage was smoke tested in 1993 to Dormouse Cave (935) and another small sink east of that site. This is also the area through which Mad Axe Woman Cave (site 1630) might come in. The stream can also be followed downstream to the complicated junction at the start of Double Barrel Passage (described in the following section).

Upstream Riaño

Upstream from Eureka Junction, the passage has some deep pools until a step up is possible and the stream flows across a sandstone floor. This can be followed round several dog legs and becomes narrow before reaching a complicated joining of ways with a prominent stalagmite on a boulder across the stream. Just before this junction an inlet enters from the left carrying the main water from upstream Riaño. However a larger dry passage enters at the complicated junction just beyond, providing an easier route to the upstream part of the cave. These parallel wet and dry passages make up Double Barrel Passage. To the right (opposite the dry part of Double Barrel Passage) an ascending 2m wide rift heads back to Grey Boulder Chamber and the entrance series. Straight ahead is a quite large inlet and this can be followed into The Mazeway.

Back at the complicated junction the main stream can be followed up the low and wet passage, but the larger dry part of Double Barrel Passage is the preferred route. This passage continues in a straight fashion for about 150m past a stal grill until the stream is rejoined. The two passages continue for another 50m in the same general direction with progress made variously in the wet or dry passage until an inlet is met on the left near the first of two large swirl domes. This inlet (Energetic Between the Legs) was pushed at Easter 2006 and in August 2006 to add 370m of new passage to the survey.

Beyond the swirl domes the passage becomes larger at a sharp left bend with large blocks on the floor. Just past this point a walking passage on the right leads into a series of "coffin level" type passage which becomes too tight after 120m. Along the way two draughting avens are found. This area is not completely explored. Continuing along the main large sandy floored passage, a second passage leads off on the right into the same series of passages as the previous side passage. The main passage continues to another junction where the route branches. The left branch leads to Cat Print Passage, becoming a hands and knees crawl after passing an area of broken calcite. "Cat" prints are visible in the mud at this point. After 40m the passage ends in a muddy chamber and a 2m awkward climb leads to the base of an 8m high aven. This can be free climbed up a narrow slot and is the original way into the Upper Series. At the top of the pitch a number of small passages lead off and all appear to rejoin the main passage further to the southwest.

The right branch from the junction at the start of Cat Print Passage passes under an aven with a loop of rope hanging down to enable a ladder to be pulled up. At the top of this a meandering passage leads to the Upper Series. An easier route to the Upper Series is found by passing under the aven to another chamber with boulders on the floor. Here a streambed flows from left to right across the chamber. Downstream leads back into the "coffin level" series of passages. Upstream continues for around 150m until the survey ends(?). Across the chamber to the right a passage leads to a cross rift. At this point a sandy slope leads up to the left, and is the start of the Upper Level Link route to the Upper Series. At the top of the slope it is possible to climb up 4m in a narrow rift to gain a chamber formed in a bedding. From the top of the climb, go across the chamber to the left to a point where you can climb down a rift to a floor which slopes back up to the height you started at (on the reverse you need to traverse across from the top of the slope to regain the top of the climb down). Just beyond this the passage emerges into the large phreatic passages of the Upper Series.

Energetic Between the Legs Inlet

Starting as a tight awkward rift passage requiring some flat out traversing, Energetic Between the Legs enlarges to a trenched meandering stream passage which is high in places. About half way along this length the passage changes to a long straight narrow rift until eventually it breaks out into a larger area above at an aven. The top of the aven can be easily reached by climbing up in the rift a few metres before the aven is reached, to gain the floor of a chamber of hanging death roof pendants which resemble large teeth (the Molars of Doom). This area contains much broken and unstable looking rock hanging from the walls and ceiling (care!). The stream continues beyond the aven in a too tight slot in the floor.

The top of the aven is in the corner of the Molars of Doom chamber with a sandy slope leading up to more stable ground. A dry meandering inlet passage also enters at this point from the left wall (when looking up the slope) at the top of the aven, and has been pushed for around 50m until the going became too arduous (unsurveyed). Up the sandy slope a crawl under a large boulder gains a further ascent to the top of the chamber where the passage narrows again. Up to the left a steep climb up loose sediment has not been attempted. To the right a step across onto a sediment floor quickly chokes where some helictites can be seen. Continuing into the narrowing passage a hole up on the right leads into a small chamber where another hole at the foot of a boulder slope gains a low wide passage with dark roof pendants which come down to the floor and sparkle with crystals. This passage leads into a large chamber (24m x 4m x 5m). Up to the right from the sparkling pendants leads to a climb up into passages above the chamber. Described from where you first enter the large chamber, to the left leads to the end of the chamber where the way on is choked with sediment. This passes under a rift in the roof which is blind. Straight on across the chamber leads into a winding crawl which ends at a double constriction with a draught, and space visible beyond, but too tight to pass. At the right end of the chamber a passage seen at the top of a climb up the opposite wall soon chokes. Turning right at this end of the chamber a climb up leads into a phreatic roofed continuation of the passage. A second climb up leads to a junction. Left at the junction leads to sediment choke. Right leads past a fine swirl dome to a dead end. An ascending calcite floored phreatic tube leads up above the climb and ends at a calcite blockage. Below the climb is the alternative route down back into the passage with the sparkling pendants.

Part way up the sandy slope in the Molars of Doom chamber it is possible to climb up to the roof and traverse back over the aven (exposed!) to gain a phreatic roof tunnel with a flat out crawl over a false floor. A pretty section of passage follows where you leave deep footprints in the sandy floor, past some formations until is closes down to a body sized tube. This emerges 3m up the wall of a large chamber with a 5m deep pit in the floor at the bottom of a conical funnel of loose rocks and sand. The near edge of the pit is a thin suspended false floor of loose fill. A tantalising slope leads off at the bottom and the pit has not been descended. Past the pit the passage continues a short way before closing down abruptly at a 180 degree bend. There is also a possible way on at roof level opposite the point where you enter the chamber. A crawl space can be seen to continue for up to 20m before going out of sight, but attempts to scale the 4m loose sediment wall to access this passage were unsuccessful due to lack of any suitable equipment.

Upper Series (still to be edited)

The main passage in this direction is an impressive phreatic tube varying between 5 and 10m high and wide. A passage on the right becomes too small at a choke though there is an alternative way back to the main passage by traversing round The Pit, a large hole which has not been descended.

Continuing in the main passage through a flat roofed area the passage gains height and width. After an awkward climb over boulders another passage is met coming in from the right. This is very well decorated and splits after 50m at the base of a 3m climb. The right branch is choked by stal after 120m but the left branch although smaller has not been explored to an end.

Back in the main passage the lofty gallery continues for some 100m until an inlet is met from the right. The passage now closes down to a miserable flat out crawl in the stream with a calcited choke above. The strongly draughting crawl has been connected to the Second River Inlet in Cueva de la Hoyuca (107). The inlet on the Riaño side of the connection has been followed to a high rift passage which after 200m finishes in a high aven and a choked chamber at a lower level. An search in this area for a "pitch 8m" failed in the summer 2010.

In the summer 2012, one trip surveyed passage due south of Pete's Way in the Upper Series adding 91m to the length.

Grov write up

In 1991 the downstream passage was pushed to major extensions which needs writing up by Paul Stacey etc. In this area, near the end of the downstream passage some 46m was surveyed in 1992. The inlet passage splits into 2 smaller inlets about 30m from the main passage. Both go to major choked areas. The right hand inlet has been followed into the choke for about 30m.

About 15m further downstream on the left is a steep boulder slope to a climb up boulders into a chamber on a fault with two avens in the roof. The inlet passage across the chamber has been followed along walking passage to a low crawl and choke. None of this 91-92 extension is on the graph survey.

At Easter 1993, a pitch was descended on the right hand side of the main passage, some way from the Anastomosis climb.

L. Mills located individuals of Cantabroniscus in 1985.

Over 3 days in December 2007, the 89cents Tinto Extension (248m) was made. This sets off in a series of climbs and traverses heading southwest from the vacinity of Cat Paw Print Passage, apparently ending 3m below the surface some 70m from the nearest site in the "Hoyuca-Riaño corner".
This was re-examined at Easter 2008 along with the Acid Bath and Pray Aven - descriptions to come. The Easter 08 trips added 154.7m to the length.
Over Easter 2009, bolting up Daddy Aven (off 89 Cents Tinto passage), started in 2007, was completed. The first level was reached at about 10m (with no passage) and continues in a scramble / free-climb with a ladder to reach another 15m in height to a calcited slot with a choked, body-sized chamber. Some new exploration also occurred down a flat-out crawl heading away from Acid Bath Chamber. A passage to the left of the aven was pursued to a steep slope where a chamber with stals can be seen through a tight squeeze.

In the summer 2011, the area off the Acid Bath (heading towards Hoyuca) was looked at and the write up appears here. The was also a trip to the most southern passage where a pitch was descended. The writeup appears here.

   Over Easter 2018, the Matienzo Karst Entomology Project (led by Tom Thompson) followed up a previous study by collecting bugs, spot sampling and setting pitfall traps in a number of sites under a Cantabria-wide permit. The Entomology Project carried out some work in this cave without collecting or sampling.

The cave appears on the Cueva Hoyuca and the Four Valleys System Hydrology diagram.

The speleo club Viana (from Guadalajara) have published a number of documents (descriptions & surveys, including gpx, pdf and jpg files) relating to the system. See their Cantabria page and the Zona de Matienzo section. [This appears to be open only to registered members with new members not allowed!]

References: anon., 1974b (logbook); Cope J, 1974; anon., 1974a (survey); Fernández Gutiérrez J C, 1975; Kendal Caving Club and Manchester University Speleological Society, 1975; anon., 1976 (logbook); Cope J et al, 1976; Mills L D J, 1981; Manchester University Speleological Society, 1982 (survey); Mills L D J and Waltham A C, 1981; Corrin J S and Smith P, 1981; anon., 1984 (logbook); anon., 1985b (logbook); Corrin J, 1986; anon., 1986 (logbook); Corrin J, 1987 (survey); material in file; anon., 1987 (logbook); Cawthorne R, 1987; Corrin J and Knights S, 1988; anon., 1988 (logbook); Davis J and Corrin J, 1989 (photo); anon., 1989 (logbook); anon., 1991 (logbook); Corrin J, 1992a (survey); anon., 1992b (logbook); Cawthorne B, 1992; Corrin J, 1992b (survey); anon., 1993c (Easter logbook); anon., 1993b (logbook); Fernández Ortega F, Valls Uriol and Maria del Carmen, 1998; García José León, 1997 (survey); Corrin Juan, 1997c; anon., 1999a (Easter logbook); anon., 2001c (Summer logbook); Corrin Juan, 2001a; Corrin Juan, 2003c; Corrin Juan, 2005; anon., 2006b (Easter logbook); anon., 2006d (summer logbook); anon., 2006e (autumn logbook); Corrin Juan, 2007; anon., 2007b (Easter logbook); Corrin Juan and Smith Peter, 2007 (photo); Corrin Juan, 2007a (photo); anon., 2008c (Easter logbook); anon., 2009a (Easter logbook); Corrin Juan, 2010; anon., 2010a (February logbook); anon., 2010c (summer logbook); León García José, 2010 (line survey); Corrin Juan, 2011; anon., 2011b (Easter logbook); anon., 2011d (summer logbook); anon., 2012d (summer logbook); Corrin Juan, 2013a; anon., 2015c (summer logbook); anon., 2016c (summer logbook); Thomson Tom, 2016; anon., 2018b (Easter logbook)
Entrance pictures : yes :  draught at the entrance (video by Jon Whiteley)
Underground picture(s):
Photos from Easter, 2013 by Tom Thomson.
Photos from summer, 2010 by Steve Sharp.
Photos from Easter 2007 by Paul Fretwell.
Photos from 2006 by Paul Dold
Photos from December 2006: Up and beyond Schoolboy Error Aven.
Video : Downstream, summer 2015 (YouTube) : Connection through from site 575 resurgence including almost real time dive out (YouTube)

Detailed Surveys : 21st Century resurvey
2008 24th Jan Hoyuca entrance & Riaño B&W png file
2008 24th Jan Hoyuca entrance & Riaño colour png file
2009 Upper level 1 B&W png file
2009 Upper level 2 B&W png file
2009 Whole cave with part Hoyuca colour png file
2010 Entrance Series & HSC colour png file
2010 Riaño + Hoyuca ent. series colour png file
2011 Riaño colour pdf file
2011 Riaño + Hoyuca ent. series colour pdf file + notes
On Paul Fretwell's latest version of the Fours Valleys survey

Line Survey : 4 Valleys System line survey (2010)
On area survey :
Survex file : Riaño only (after Easter 2018) :  4 Valleys System & surrounding caves (after end of Easter 2018)(Coordinates altered to fit ETRS89 datum, April 2014.) : just 0105 + 3234
Passage direction rose diagram: Four Valleys System
Hydrology (Terry Whitaker): Hoyuca and the 4 Valleys System