Las Grutas de Los Rios San Jeronimo and Chontalcoatlan - World Class Through Trips

Located just 30 km from the famous historic silver district of Taxco, and 100 km SW of Mexico City lies the Dos Bocas System which features the dry fossil tourist cave of Cacahuamilpa situated above the active river caves, San Jeronimo and Chontalcoatlan (or Chonta). The river caves are two independent, almost 6 km long, caves that have lower entrances within 100m of each other (thus the Dos Bocas name - two mouths in Spanish) and can both be done as separate through trips. All three caves feature enormous passages for their whole lengths and truly make up one of the most impressive cave systems in Mexico and surely one of the classic through trips in the world. And what other cave in the world can boast that it had a volcanic lahar flow through its whole length and continue 30km further downstream?

Cueva Cacahuamilpa has been known about for probably hundreds of years and has been a tourist cave since the early part of this century. It was first mapped in the 1920's and is essentially a level 2km long passage of borehole dimensions (averages about 40m wide by at least that high) and is extremely well decorated with floor to ceiling flowstone or columns in places. Having it lit up for the tourist trip is really the only way to truly appreciate it.

For active cavers though it is the lower caves that hold the real attraction for both have almost 6 km of sporting river passage in caves that average 40m wide by 40m high. To get to the entrance of C. San Jeronimo you can hire a local truck for a dollar a person to drive you from the tourist entrance over the mountain to where you must then walk downhill for 200 vertical meters, first into the dry fossil river passage and then to where it intersects the very active present river course. It is so active that the cave is generally not passable from the end of the rainy season in Sept. through to about New Years and the river formed by the joining of the waters of the two caves is paddleable all year round (nice class 3 whitewater). Numerous people have died trying it at the wrong time of year as all the crosses near the entrance attest to.

Before entering the river many people suit up with wetsuits if it is in Dec. or Jan. as the source of this river is meltwater from the snows on Volcan Toluca 50km up stream. Most sane people just wait a little later in the year for the water levels to go down and the temperatures to go up so they can do it in shorts and tee shirts. My first visit was planned to catch as much high water as we thought our group could handle but happened to correspond to a late Jan. snow fall on Volcan Toluca. Most of our group of twenty did have wetsuits and even those that didn't did not complain of the cold, even the 72 year old aunt of the trip leader.

You can't even see the actual dripline entrance from where you must enter the river due to the initial canyon which is about 10m wide by at least 40m high and which forces you to swim shortly after entering the frigid water. After about 100m you can wade again and see the true entrance high above you though it is still another 200m before the cave opens up into the cave passage proper. Here you are overwhelmed by the shear size of at least 60m wide, 70m high and still well lit of coarse. In fact it is at least 500m further in before the light finally disappears and you are left to guess how far away are the walls if you don't have enough people and/or lights in your party to see. This is one of the advantages of a large group especially when you are the last in line and the long string of lights enables you to actually see the whole outline of the enormous passage.

The route to take dependents on what you consider to be the line of least resistance. In places it is definitely easiest to walk along the sandy embankments while in others wading in the smooth bottomed river preferable. But when there are slippery rocks hiding beneath the surface as is more common and there is no flat sandy beach it is necessary to scramble over boulder piles some of which can take you up to 30m above the river level. And as it is an active river last years easy bypass to that cascade may mean that this year you must slide down a large boulder ramp and plunge in to the pool below to carry on as we had to. Numerous swims are necessary though none is as long as the one in the entrance area. Occasionally there are some large gour pool flows (that are referred to as fountains in Spanish as they resemble a cascading fountains without the spouting fountain part) which are well worth a scramble up to check out. The largest one stretches at least 100m along one wall and at least 50m vertically up it at the half way point and makes a good spot to stop for a snack, or a full on lunch in our case. Everyone had been worried about freezing before we started but all they could think about after three hours was food.

About two thirds of the way through the ceiling finally comes down to where you can easily see it, about 10 to 20m high and you start to notice the draft. There can't be many cave passages of 5m height and 25m width where you can feel not only a draft but is strong enough to blow out a ceiling burner carbide lamp. Next time we want to take in a kite to see how it flies. The claustrophobic types need not worry for it opens back up again to its more normal dimensions.

The lower entrance is just as impressive as the upper one in its own way and also takes at least 500m of gradually increasing light levels before you even see blue sky again. The swifts (or golandrinas) who have been watching tourists come and hike down from the tourist cave above all day long no doubt get a bit of a surprise when the occasional group of light bearing figures comes out of the darkness above which they are nesting. Now all that remains is to hike back uphill to the parking lot and your car. The normal traverse time for Mexican excurcionistas is about eight hours, while our group of twenty which ranged in age from nine to 72 made it in seven. It has been done in as little as 2 hours (by the late Boxhead and company) but they didn't see any of the nicer formations. It's definitely worth the time to go slow and savour it all.

{A geologic note for those of you wondering just what is a lahar. A lahar is a cold volcanic flow produced when there is a cataclysmic eruption of a volcano that has glaciers on it. The hot gas and particle laden eruption cloud emitted from the volcanic vent raises, but then collapses sending the same hot, particle laden gas cloud down the flank of the volcano past the glaciers which quickly melt from the heat. The now cooler, but combined mixture of water, ash particles, sand, rocks etc. rushes down the slope sweeping away anything in its path and incorporating that into the flow. The resulting lahar (or mud flow) can travel many tens and even hundreds of kilometers away from the volcano. In the case of the three caves of the Dos Bocas System (all of which have these deposits still plastered on the walls all the way up to the roof) the lahar flowed 50km from its source, passed through the caves, and continued some 30km more downstream. The best guess of the age of this flow is 28,000 years B.P. and definitely wouldn't have been a good day to have been caving.}

It was a year later before we got around to organizing a trip to see C. Chonta and decided that we must photograph it as there are very few known photos of these caves and those are very old. Rumors of an unexplored big room off a side passage in Chonta added to the appeal of the trip. We planned to hike up and over to the entrance Sat. morning and push the side passage in the afternoon and then bivy overnight just under the dripline and photograph on Sun.

Knowing that you are going to a Big cave still doesn't prepare you for the size of the entrance. The fifty meter wide opening is located at the base of what must be close to an 600m high vertical wall and is made all the bigger by the side passage heading off it that is best viewed from the opposite cliff while downclimbing. Without doubt the scariest part of the trip is downclimbing a fixed, overhanging, ladder held together with baling wire. Sensible school groups belay their students down this part.

As everything in this area is big, we should have realized that the 'climb' up in to the entrance Ramón mentioned wouldn't be a scramble. It turned out to be a 25m tall, 5.8 climb, sporting an overhang near the bottom and ending with a vertical section up a moss covered flowstone formation, all with little protection. Not only had we not brought harnesses and climbing shoes, the person Ramón expected to do the climb canceled out the afternoon before. Fortunately I had invited Dave Jones along and he quickly got it over with despite being equally unequipped. While Dave, Ramón and Curro went ahead to survey, Kirk and I photographed our way in.

The passage name of Pilars is quite appropriate as beautiful white columns (or pillars) graced the entrance sections (some well over 15m high) along with large gour dams, dry at this time of year. The nice part ends quickly though forcing one into a nasty crawlway. Not a flat, sandy floored one as I had been dreaming about, but a tight, contorting, sweat producing one, punctuated by the occasional pile of putrid vampire guano that you had to try and pass without smearing on yourself. Reminded me a lot of the entrance section of Darren Cilea in Wales, though its temperature precluded the use of a nice protective cave suit. We caught up to the surveyors after about 150m as they were paused at a duck under. Nobody was very keen to get their only clothes wet, especially as it seemed someone else had surveyed in at least this far before us. Kirk decided to go for it and coaxed Ramón and Curro to continue on where they did eventually find the fabled big room along with the names of some people from the 50's marked on the wall. Somewhat anti-climatic, though a passage did continue on the other side in a similar crawlway that looked un-entered. As this Pilars passage looks to be the original cave route before being plugged by the lahar flow, this crawl has good potential. Perhaps another time.

Bivying in the entrance meant that we were well positioned for a good start in the morning but also meant that we had to listen to the near continuous parade of groups starting their trip. For some reason Mexican excurionistas like to do the cave at night, entering around sunset, and coming out after midnight. Though as this weekend happened to be one of the few long weekends Mexicans get they were out in force and a new party passed us by every hour, all night long, whooping and hollering as they hit the cold water. This in turn woke up the swifts nesting high above us and their racket combined to give us a restless night.

We did manage to get going before the crack of noon (just) and thoroughly enjoyed strolling along the huge passage. And there is even another un-explored side passage, at least 10m in size some 10m up one overhanging wall not far in from the entrance (a future project for Dave). It seemed to me that Chonta is actually a bit smaller than San Jeronimo, but was very consistent in its 30m width and height. It is also a lot easier in having more sandy beaches to walk along and less boulder piles to climb over. Occasional large gour pools formed below inlets creating perfect places for the Mexicans to spray paint their names. (Boy scout groups here don't have the same leadership as in other countries) Almost exactly half way through the cave passes beneath the Claravoya Entrance, which has a very impressive flowstone and gour pool cascade that flows water every rainy season down its 60m height. The lower section went by quickly as we weren't stopping for photos, partly because the marble band here is not as pretty as the section in San Jeronimo. The original explorers in the 1930's got down here to within about 600m of the bottom entrance and turned back within one corner of the sight of daylight. We got out in time to savour that daylight and tromped back up to the cars with considerably more energy than the previous years trip through San Jeronimo.

So if you are ever visiting Mexico I highly recommend a trip through at least one of these three caves. The best season for the active ones is from about Xmas through to June / July. As mentioned, trying them in the rainy season is most likely to result in loss of life and while there is a local cave rescue group, they usually just do body recoveries. Happy caving.

Article and Photos By: Chris Lloyd