By ANDREAS KLOCKER | Southern Tasmanian Caverneers, Hobart, Tasmania, Australia
March 2016, and I’m off to Mexico again – the third year in a row. The previous two years I joined the Proyecto Espeleológico Sistema Huautla (PESH), an American-led expedition with the goal of continuing exploration of Sistema Huautla, a 1545m deep and about 75km long cave system located in the Mexican state of Oaxaca (see here for an article of last year’s trip).
The furthest explored downstream part of this cave system is a huge Sump known as “Sump 9” or “The mother of all Sumps” which had been discovered on an expedition led by Bill Stone in 1994 (Stone and am Ende, 1995). Also have a read of Beyond the Deep: The Deadly Descent into the World’s Most Treacherous Cave by Bill Stone and Barbara am Ende for an interesting account of this trip (Stone, et al., 2002).
It was only in 2013 that cavers returned to Sump 9 on a British expedition organised by Chris Jewell. On this trip Jason Mallinson and Chris Jewell pushed Sump 9 to a depth of 81 metres at 440 metres penetration, with the underwater tunnel barrelling off to greater depths (Jewell, 2013).
One of the great mysteries of Sistema Huautla is its connection to the active resurgence in the Santo Domingo canyon some 10 kilometres away. This resurgence has been confirmed by dye trace and has been the subject of several expeditions, each of which has increased the known length of the cave and closed the gap to the end of the line in Sistema Huautla’s Sump 9. In 2001, Brits Jason Mallinson and Rick Stanton explored and surveyed the resurgence to just over 1 kilometre distance to an air bell where a passage was seen heading off 10 vertical metres above water level, but the upstream continuation of the underwater river remained a mystery (Shade and Stone, 2002). This has now been 15 years ago, with nobody having returned since.
Have a look at the schematic to get an idea of Sistema Huautla relative to its resurgence – only the most convenient/quickest route to Sump 9 via the Fools Day Extension in San Agustin is shown on the left; the resurgence is shown on the right, ending at its most upstream end in an air bell found by Jason Mallinson in 2001; the Cueva de la Peña Colorada is a fossil overflow resurgence (still pumping loads of water in winter) and is assumed to be part of the drainage system of Sistema Huautla (even though it has never been successfully dye-traced).
All of these Sumps – Sump 9 in San Agustin, Sump 7 in the Peña Colorada, and the upstream end of the resurgence – are going leads with large tunnels heading into the unknown. Having read about all these previous expeditions, and with the potential of an estimated 15 kilometre long and over 1750 metre deep through trip in the back of my mind, I felt the urge to close this gap and started to plan the expedition.
So the idea was there – to continue at the current end of exploration in the Huautla resurgence and work towards Sump 9.
Now it was time to put together a team and figure out how to deal with some of the logistical hurdles, such as transporting large amounts of dive gear to the remote Santo Domingo Canyon and getting permission from the locals to access the cave.
Luckily, even though cavers with good skills at both dry caving and rebreather diving are about as abundant as the Yeti, we quickly had a great team together. It included Zeb Lilly, who I have been caving with since my first trip to Mexico, and Dave Bardi, Sandy Varin (who both also have been caving with PESH the previous year) and Craig Howell, who have been spending the last decade or two pushing the cutting edge of rebreather diving and over the last couple years became addicted to dry caving. And then on one of my annual work trips to the UK I talked to Chris Jewell and Jason Mallinson about my plans, and luckily it didn’t take much convincing to get them to agree to join us. Unfortunately, work-related issues stopped Jason from coming along and Craig managed to fall over with a twin rebreather on his back injuring his shoulder, and so we were down to a team of five.
We were also lucky to have great non-diving support with us. Ernie Garza, a Texas-based caver with decades of Mexican caving experience and fluent Spanish skills, travelled to Santa Ana Cuauhtémoc, the town which we were planning to use as our base, two months prior to the expedition to organise accommodation, ask about permission to access the cave, and have a look at the newly-built road into the Santo Domingo canyon.
And then Ernie planned to drive with us from the US to Mexico to help us set up the expedition. An absolute champion! Our other amazing support was Alejandra (or Alex as we called her), a student from Mexico City who joined us as a cook, translator, and expert in diplomacy – the key for us to building a great relationship with the locals. Leading up to the expedition we also had great support from Bill Stone, who led many trips into the Santo Domingo Canyon before and hence was an invaluable source of information.
After a year of planning it was time to head off, and the whole thing worked out a bit like this. Zeb drove his humongous truck (a Ford F350, aka the battleship), filled with an amount of dive gear which would put any dive shop to shame, from Virginia to Dallas where he picked me up from the airport; we then continued on to Bill Stone’s place in Austin/Texas where we drank beer, picked up Ernie and additional dive gear which the US Deep Caving Team (USDCT) was generous enough to lend us.
The next day we crossed the border where Ernie explained to officials the purpose of our trip and the gear in the truck, and Zeb did the paperwork to get permission to drive the vehicle in Mexico (which had to be done by the vehicle’s owner). Zeb then walked back over the border to the US where he had to work another fortnight before joining us, and Ernie and myself drove for two days to Santa Ana Cuauhtémoc on the south side of the Santo Domingo canyon.
Thanks to Ernie’s previous visit to Santa Ana it only took us about twenty minutes to organise accommodation with three rooms for gear, cooking and sleeping. Luckily we even had a little food store selling cold beer a stone-throw across the road and owned by our landlord.
Now it was finally time to go caving! Our plan was to first find our way down the canyon, locate the cave, and figure out a plan for the next few days once we knew a bit better what the resurgence and the hike through the canyon were like. So we filled the battleship with gear and drove down the steep slopes into the canyon, about 1300 metres vertical, which turned out to be quite a challenge with steep drop-offs next to the road and sharp corners which were obviously not built for the length of vehicle we were driving. Nevertheless, after numerous scary moments looking down a steep drop too close to the tyres of the truck, we reached the river bed and happily left the truck behind. From there it was only 40 minutes of easy hiking with three shallow river crossings until we found the resurgence — which we easily recognised, thanks to photos from the 2001 expedition which Bill Stone had sent us.
After climbing over some boulders in the entrance we finally saw what we were here for – an amazing looking Sump pool. Around a rock feature we noticed a bolt and some remnants of old dive line from one of the previous expeditions. The cave entrance provided enough space, sheltered from weather and out of sight from visitors, to store diving equipment, with enough space left for two people to gear up at a time.
After the recon we then headed back, looking forward to the upcoming dives, and enjoyed one of many great dinners cooked by Alex. This trip from Santa Ana to the cave entrance took us about three hours that day, but after practising high-speed three point turns in the battleship we subsequently reduced this to two hours door-to-cave.
Luckily, due to amazing scenery in the canyon this daily slog never became too boring, apart from a few misty evenings when the visibility was so bad that the cold beer seemed a damn long time away. Only one slight worry remained for our daily commute – driving up 1300 metres of elevation is probably not what a diving doctor would recommend after a big dive, but with an emergency oxygen tank which we kept in the battleship, and some magic medicine known as beer waiting on arrival at home, what could possibly go wrong?
Relining the sump
Once set up at the cave we we were very keen to finally get into the water. The general plan was to have two divers in the water every day, with the others helping to porter the gear, and re-line the sump to the point to which Jason got to in 2001. The first dive was done by Chris and myself, with me running the reel and Chris following in close proximity to improve/add some tie-offs. I have never laid line as a two-person team, but due to the cave’s size and complexity, combined with only 5-7 metres visibility and hence me swimming into lots of dead ends before finding the way on, this technique worked a treat.
We soon reached the end of Sump 1 ±400 metres into the cave where it ends in a pool with the character of a bubble bath caused by a ±1 metre waterfall hitting its surface (as described in the trip report from the 1995 expedition; (Stone, 1997)). Nevertheless, in 2001 Jason and Rick were lucky enough not to encounter this waterfall due to higher water levels, and we were hoping that this would be the case again, but bad luck for us — even though a vertical metre is not much, it did cause us some trouble due to the need for climbing sharp rocks in a drysuit and hauling tanks, all against a very substantial flow. The waterfall also forced us to leave the 45kg scooters we planned to use in the second Sump at our accommodation and enjoy long swims and decompression stops instead.
The next day we planned to carry Dave and Sandy’s rebreathers to the Sump so they could start to re-line Sump 2. But as it frequently happens to everyone diving rebreathers, gear does not work as it should, leading to a lot of gear fiddling and the use of inappropriate language.
In this case, attaching the slightly odd-shaped carbon tanks onto Dave and Sandy’s rebreathers led to a leak into the scrubber, and so they had to experiment with different gear configurations to solve the problem (note the funky bottle configuration on their rebreathers in the photos). Once the gear was ready to go it was already quite late in the day, and hence we decided to stay in town and spend time properly setting up our fill station, including the compressor, two boosters, several large storage tanks of oxygen and helium and a whole lot of transfer whips.
The next dive was, after successful gear modifications, done by Dave and Sandy who rigged several ropes over the waterfall to both attach gear and as a handline. They then continued into Sump 2 and started re-lining the sump. During this dive they stayed on the right side of the tunnel since remaining bits of old dive line from the previous expeditions made navigation easier. On the way out they left two cylinders of deep mix at the beginning of Sump 2 and returned on a single tank of bailout each filled with air. This made the transition over the waterfall much easier on the next dive, and from then on we always only brought back cylinders with deep mix if they were in need of a top-up.
High flood flows
While Dave and Sandy were busy in the cave, Chris and I hiked up the then main entrance of the Cueva de la Peña Colorada. which took us about one hour of scrambling, swimming and climbing while keeping an eye out for some poisonous snakes which apparently like to hang out in the pools of the canyon. It was easy to find the entrance due to the huge dry river bed leading up to it. What really impressed me about this cave entrance, which we could only follow for ±100 metres to the first sump, were signs of extremely high flow during winter floods. The dark limestone was polished like I have only seen in the Upper Gorge in San Agustin the year before, and the gravel we walked over was shaped wave-like as you see on the bottom of a high-flow sump. And all the signs of previous explorers had been washed away.
Once we got back to Santa Ana the work for the day was not quite over. On arrival Alex told us that the big wigs of the local farmers association wanted to talk to us. So not knowing what to expect, Alex, Chris and myself headed over into the centre of town to meet them. Apparently we didn’t ask all the necessary permissions for permission to dive the cave, or more accurately to use the road into the canyon which apparently belongs to the local farmers association. This resulted in a long discussion between Alex and the locals, while Chris and I sat there trying to pick up a few words of Spanish to try and find out what’s going on. Luckily an hour or so later, after Alex using all her diplomacy skills and us agreeing to chip in for some beer for the farmer association’s annual party, everything turned out fine and we had all the permissions we needed.
The day after Chris and I hoped to continue laying line through Sump 2, but Chris woke up with an upset stomach and decided not to dive. Hence I made the decision to go for a solo dive and spend some time checking for possible leads in Sump 1. Due to the average visibility in the cave and it’s large size and complex structure we found many locations where we could have missed possible leads. Nevertheless, after lots of searching I was convinced that we actually had found the one and only way on. From there on Sump 1 turned into a regular commute and we fully concentrated on pushing Sump 2.
On the next dive Dave and Sandy continued laying line in Sump 2 until they reached a depth of 55m beyond the 65m deep point of the sump. At this point they made the decision to turn due to the oxygen in their rebreather tank becoming low as a consequence of the cave changing depths repeatedly, especially in Sump 1. Whilst Chris and I carry two oxygen tanks on our rebreathers as standard configuration, after this dive Dave and Sandy then started carrying a second oxygen tanks as well to avoid this problem on upcoming dives.
While those guys were gone, Chris and I continued our surface exploration and hiked upstream through the Narrows of the Santo Domingo Canyon, named appropriately since the canyon walls come very close together and the river deepens, occasionally turning the walk into a swim. On the other side of the Narrows we had a look at both the HR resurgence and the Cheve resurgence. The HR resurgence has an entrance a little similar to the Huautla resurgence, but smaller, and it was possible to follow the stream for several hundred metres before we got stopped by a sump, ±1×1.5 metres large, similar to what is described in the old trip report (Stone, 1988). Even though this sump is not that large and in the old trip report is considered as not diveable, I think it is definitely worth returning with some open circuit sidemount gear. We then continued on to the Cheve resurgence where we poked around in many of its dry entrances and admired the very clear, but very cold water coming out of the resurgence.
After Dave and Sandy returned the previous day, they mentioned several places in Sump 2 where they lost visual contact with the left side of the Sump, leading to the possibility of a junction, and hence other ways on. This also agreed with a possible junction ±400 metres into Sump 2 which Bill Stone mentioned previously. Hence Chris and I planned to dive Sump 2 and run a line across to the left side of the tunnel on several occasions, checking every possible lead. We did this to a depth of 45m, and after a few dead ends and some silt-outs away from the main flow, we decided that none of these promising looking junctions went and returned.
On the way out I then managed to puncture the wrist seal of my dry suit while jumping over the waterfall into Sump 1 (something Sandy has already managed to do a couple days earlier). Dave and Sandy then continued the next day with the same mission from the point where where Chris and I turned, but also couldn’t find any other possible ways on.
As things happen on an expedition, we then had to take a day off to find diesel for the battleship and repair a slow leak in one of its tyres. So Alex and myself headed to Chiquihuitlán de Benito Juárez (no-one apart from Alex could pronounce that name, and so we simplified its name to “ChiChi Monkey”, and once we found out what “ChiChi” means, to “Cheeky Monkey”) which was a 25 minute drive away with a guy who could fix tyres and another guy who could organise diesel (which he subsequently siphoned from several jerry cans into the 140 liter tank). In the meantime the others did what we always ended up doing in any spare minute – fix and service gear, and in between enjoy Alex’ great cooking!
After multiple days spent searching and laying line, knowing that we were getting close to the airbell Jason found in 2001, Chris and myself set out to hopefully finally reach the surface beyond Sump 2. Sadly in Sump 2 my Scurion head torch flooded (due to 100% user error – this light is probably the best gear investment I ever made) and I turned the dive after dropping a stage tank of 50% Nitrox, with Chris continuing on himself with three bailout tanks.
On this solo dive he managed to find a way on beyond where Jason surfaced in 2001, and decompressed in the new tunnel until he reached a depth of 12m. At that point he decided to return and leave the lead to Dave and Sandy who could get to that point with less decompression obligation.
Dave and Sandy then continued on from Chris’ furthest point and surfaced into dry passage! This point was now over 1km into Sump 2 beyond a deep elbow in the passage at 65m, so a substantial commute – without surveying or laying line, the dive in Sump 2 took ±1.5 hours each way, half of which was spent decompressing.
Still dressed in their drysuits, they spent two hours bagging dry passage, exploring everything they could safely reach with their drysuits on, before starting the long dive back. Most of this dry passage was large walking tunnel, with a mix of gravel banks (which looked just like the underwater portion of the tunnel), clean dark grey limestone, cracked mud, and beautiful decoration. About 150m into the Sump they found a deep looking Sump pool (now named the “Distraction Sump”) to the side which Dave checked out with a mask but no dive gear. This must have been one of Dave and Sandy’s most amazing day’s caving, with so much dry passage beyond a sump being a big dream of most cavers. They named this new cave passage the “Passage of the Cheeky Monkey”.
Dry suit territory
Chris had to leave back to the UK for work before we finished up with the expedition, so the day after, on his second-last dive, Chris and I returned into the new dry passage. After spending so much time searching for the way on underwater and listening to Dave and Sandy’s stories we were both very excited about seeing the new dry tunnel.
On the way in Chris first surveyed in Sump 2 from 20m depth to the the sump pool in the new dry passage. After de-kitting on the amazing beach in the dry tunnel we then continued on (still in our drysuits) and surveyed ±600m of dry passage. On the way out Chris took photos of the passage to make sure we have some documentation of this amazing place. All this made for a very late exit out of the cave, but who cares if you have had such an amazing day in virgin cave and with a cold beer waiting at home!
The next day Zeb was meant to arrive in Teotitlan together with Mark Minton and Vonnie Droms who were continuing on to the PESH expedition to push La Grieta. So we headed down the mountain in the morning to spend a day in civilisation, go shopping, eat in a restaurant and just relax.
But on the way down we ended up with a flat tyre, and having a closer look at all the other tyres, decided that fixing won’t get us far – they all needed replacement since they all looked like they are going to give up in a very short time. Hence, after Sandy showing us her tyre changing skills, we aimed directly at the nearest tyre dealer, a guy who calls himself Mr Fast, and who after some phone calls promised us a set of new tyres in the afternoon. This worked out well. We continued on to town, met Zeb at the bus station, had some food, and returned to Mr Fast and his dog Tyson who were already waiting with the new tyres. Quite some time later we then returned to Santa Ana.
With all of Zeb’s gear still in pieces, we decided to have Dave and Sandy dive into Sump 2 to continue surveying from the 65m deep point to the point at 20m from where Chris previously surveyed to the new dry passage, and Zeb was going to finish setting up his gear and go for a familiarisation dive into Sump 1. I guess we didn’t tell him in enough detail about what to expect at the far end of Sump 1 … and when he got close to the surface on the far side he thought that a tank blew off gas, whilst it was really ‘only’ the waterfall causing havoc – that’s definitely not something you experience on your average cave dive!
Now with Zeb, who is also our survey expert, ready to dive, the plan the following day was for Zeb and me to dive to the Passage of the Cheeky Monkey to finish off the surveying and find a way on, while Chris was going to join us in Sump 1 to take some underwater photos, and then head back to disassemble and pack his gear. But as things go, it took Zeb a bit to get used to our funky setup of the bailout tanks (the sort of rigging you end up with if you patch together all the bits of gear you borrowed of different people), and so he decided to abort the dive and we finished the day early with some nice underwater photos from Sump 1.
Dave and Sandy’s plan for the next dive was to look at a lead they saw beyond the 65m deep point, at ±38m, to hopefully find the way on upstream. After getting through Sump 1 quickly, they noticed while getting ready to descend at the beginning of Sump 2 that Sandy’s (brand new) first stage of the regulator started blowing off through the over pressure relief valve.
This would have drained one of the two oxygen tanks she was carrying in no time, and even though this apparently amazing looking lead was stuck in Dave and Sandy’s head, the only sensible option was to abort and head home. So we got back early where we met up again with Chris who stayed in town that day and pack his gear for a departure the next morning and drink as many beers as any British caver would when not underground.
With Zeb having adapted to the gear configuration, we both headed to the Passage of the Cheeky Monkey the next day to finish off the surveying. This dry passage is mainly made up of one major tunnel, with two little junctions towards the end where it is possible to climb into a lower level with a stream. This time we learned from our experience before, and changed out of our drysuit in the dry passage, and also brought a bicycle repair kit to fix any drysuit seals which we might rip on the far side of the Sump. I even brought a set of Teva sandals along since the cave allowed for easy progress.
On the previous trip to the dry passage, Chris and I had surveyed most of the main tunnel, so this time we connected into this survey and continued into the lower level. Both junctions led into the same stream, but with both segments of the stream being split by a short sump in between. On the furthest upstream end the water squirted out of a tiny hole, and sadly there was no way to follow the water further upstream into the north-east direction it was taking.
Slippery and dodgy
On the downstream end the water flowed into a sump which looked deep with no floor in sight. After searching for any possible continuation of the dry cave, with no success, we returned to our dive gear. Right above the Sump we could see a passage continuing on towards the south, about 10-15 vertical metres of slippery loose climbing above water level. I briefly attempted this climb but decided it was just too dodgy and so we returned. It is probably likely that this would lead to the air bell Jason Mallinson discovered in 2001. One of the things which really surprised me in the dry passage was that part of the cave looks like it never floods; some of the calcite features would break off as soon as water hits them.
On their second try Dave and Sandy finally made it their lead at ±38 metres, but to their frustration they just laid line around a large room and reconnected to the main line. We knew that the cave had to continue somewhere underwater, since there was no flow where we surfaced in the Passage of the Cheeky Monkey, but in such a large complex cave with average visibility it was no easy task to find. Since we were running out of time on this trip, on their way back Dave and Sandy brought the stage tanks from Sump 2 back to the waterfall so Zeb and I could finish cleaning up the next day.
On the way up the canyon our hopes for being close to cold beer were destroyed when we suddenly saw large amounts of white smoke coming out of the battleship’s hood. After letting it cool off a bit the problem quickly became clear – we had cracked the radiator. Since we had no tools to do any repairs of that kind we started a long walk out of the canyon. Luckily, once we reached the main road, the presidente of Chiquihuitlán de Benito Juárez and some of his buddies drove past and were happy enough to give us a lift back home where we finally enjoyed our well-earned beer!
The next day we had to find a way to get the broken down truck out of the canyon. After some phone calls to some mechanics (it was Sunday and most of them enjoyed their day off) we finally found someone who came into the canyon with us and did some temporary repair so we could drive the battleship out of the canyon.
The mechanic then ordered a new radiator and, after Alex sweet-talking the presidente of Santa Ana into lending us his truck (thanks Alex!), we left the battleship at the mechanic’s place where we were also offered some very special booze (God knows what that was – it would have definitely been strong enough to power the battleship). In the afternoon we then enjoyed a great spicy meal cooked by some locals who invited us over and then in the evening we joined the locals in their annual party organised by the local farmers association where everyone showed their dancing skills (or lack thereof).
Following a day of fixing cars and drinking booze, Zeb’s and my task the next cave in the cave was easy. We planned to dive to the waterfall, bring back the stage tanks and Zeb was going to re-survey and sketch Sump 1 (this Sump has never been sketched with only line data existing from previous trips). So while Zeb was busy surveying, I used the time to clean out much of the old line from previous trips which was still hanging in bits off several rock features trying to catch a diver.
In the meantime Dave and Sandy ran laps through the canyon to get as much gear as possible from the cave entrance to the truck. The rest of the day we all then spent doing several more trips to clean all the remaining gear out of the canyon. And luckily, against all odds, the presidente’s old truck made it out of the canyon with all the gear in the back!
Once all the gear was out of the canyon, the following day was spent packing everything into Zeb’s truck, which now had a shiny new radiator. Surprisingly, all five of us and an insane amount of gear fit into the truck, at least after we made use of the roof rack. At that point it was time to farewells and head home.
So we enjoyed one more scenic drive off the mountain to Teotitlan where Dave, Sandy, Alex and I jumped on the bus to Mexico City and Zeb continued on to join the PESH expedition in Plan Carlota on the north side of the Santo Domingo canyon.
In summary, after a year of many nerve-wrecking moments planning this trip, everything worked out much better than I ever imagined. In total we found 1232m of new cave passage, 358m of which is underwater and 874 metres of which is dry cave. The Huautla resurgence is now 2.33 kilometres long. While we were struggling to find the underwater way on, there are two undived sump pools in the dry passage which are both located north of where we lost the water flow. The logic objectives for a return are now to dive those sumps, reconnect them with the underwater tunnel further downstream to avoid having to drag dive gear through dry passage, and then continue to push the cave further upstream!
If the hypothesis that the Peña Colorada overflow resurgence is connected to the resurgence is correct, and knowing that the water-level of the most upstream Sump in the Peña Colorada is at least 110m higher in elevation than the resurgence, this would mean that we should find plenty of dry cave on the way. In short, we can’t wait to return and push on!!
As with any expedition like this, we would not have been closely as successful as we were without the great support of several individuals who spent a lot of time and effort helping us out as much as they could.
On the trip we had both Alex and Ernie help out with language barriers, local politics and great cooking. After a month in Santa Ana we had built a great relationship with most locals which I see as much of a success of this expedition as the actual exploration. This success would definitely not have been possible without those two. Leading up to the trip, Bill Stone put great effort into helping us out with any bit of information he had from previous trips, which went way beyond what one would find in any trip report. Thanks guys!!
We also had great support to get together the gear necessary for this trip. We were able to use a large supply of gear from Bill Stone and the US Deep Caving Team, the latest and greatest in dive computer technology thanks to Damien Grigg from DKG drysuits and Shearwater Research, and many custom made tools produced by Stephen Fordyce from TFM Engineering. And the fancy mixed gases we used, the absorbent for the rebreather, and the lead were funded by the National Speleological Society’s Ron Simmons Award. This sort of exploration definitely pushes gear to its limits, but thanks to such great help putting together the best gear possible we had no major gear issues and could focus on pushing the end of the cave.
The Huautla Resurgence Project 2016 Expedition
March 17th – April 17th 2016
Cavers: Andreas Klocker (AUT/AUS), Sandy Varin (AUS), David Bardi (AUS), Zeb Lilly (US) and Chris Jewell (UK)
Support: Alejandra Mendoza Contreras (MEX), Ernie Garza (US)
Jewell, C., 2013, San Agustín 2013 Expedition, AMCS Bulletin 25:33-37.
Shade, B. and Stone, B., 2002, 2001 InnerSpace Odyssey Expedition. AMCS Activities Newsletter 25:53-71.
Stone, B., 1988, Huautla: Vine Cave and Peña Colorada Canyon. AMCS Activities Newsletter 17:50-58.
Stone, B., 1997, 1995 Río Tuerto Expedition. AMCS Activities Newsletter 22:162-172.
Stone, B. and am Ende, B., 1995, The 1994 San Agustín Expedition. AMCS Activities Newsletter 21:44-64.
Stone, B., am Ende, B., Paulsen, M., 2002, Beyond the Deep: The Deadly Descent into the World’s Most Treacherous Cave, Grand Central Publishing.
- The Huautla Resurgence Project 2016 Expedition, Mexico - November 21, 2016
- Exploration beyond the sumps of Red Ball Canyon, Sistema Huautla, Mexico - November 9, 2015