Sotano de las Golondrinas

Description

BULLETIN 2of the

Association for Mexican Cave Studies

EDlTED BY

TERRY W. RAINES

Austin, Texas, U. S. A.

August 1968

PDF reprint from scans of the original, February 2011. The text in this PDF has been “read” by Adobe Acrobat and is searchable to the extent that the OCR was successful. This bulletin has been largely superseded by AMCS bulletin 10, Caves of the Golondrinas Area, by Peter Sprouse and Jerry Fant, 2002, but it, especially the color photographs, remains of historical interest.

Copyright ([) 1968 by Association for Mexican Cave Studies

INTRODUCTION

Sotano del a s Golondrinas ispresently the deepest known free­fall pit in the world. Unlike other"free-fall" record holders, the dropin Golondrinas is completely free.There are no ledges or climbingagainst a wall. The pit was fir stentered during April of 1967 andlater surveyed during June of thatyear. Pr eviously, the greatest dropthat had been descended by caversin the Western Hemisphere wasslightly over 500 feet. The 1094foot drop in Golondrinas more thandoubled this old record and thus be­came a real challenge to equipmentand technique. Using methods ofrappel and prusik previously em­ployed in other Mexican sotanos,Golondrinas was succes sfully ex­plored without difficulty.

In the following pages of text,the sotano itself is described, aswell as the area in which it is locat­ed and the early explorations. Ashort section is also included whichdescribes the climbing equipmentand techniques that have been us ed.At the very end of this booklet ar edescriptions of the eight full-colorphotographs that are contained in a

s epa rat e envelope. A two-colorcave map is also included with thisBulletin to further illustrate Sotanode las Golondrinas.

Many people contributed to thesucces sful publication of this Bulle­tin. Of greatest assistance werethe officials and residents of theAquismon area who granted per­mission and aided our explorations.John Fish and Bill Russell donatedtheir tim e and knowledge to thewriting of two sections of this Bul­letin. John wrote the Cave Descrip­tion and Speleogenesis and Bill notonly wrote the Regional Geology butalso donated mor e time to the as­s ern b 1 i n g of the Bulletin. CarlKunath, aided by John on the cavemap, is responsible for drafting allthe illustrations. Bill Deane fur­nished Figur es 4 and 5 of the photo­graphs and Carol Russell offeredher skill as proofreader. Otherpeople serving in helpful capacitieswere Gill Ediger, Michael A. San­born, and members of the Univer­sity of Texas Speleological Society.To all of the above people I amdeeply indebted.

TWR

TABLE OF CONTENTS

LOCATION •••••

CAVE DESCRIPTION and SPELEOGENESIS •

REGIONAL GEOLOGY.

HISTORY.. •• • •

EQUIPMENT and TECHNIQUES

PHOTOGRAPHIC DESCRIPTIONS. •

• • • • 1

3

. 6

• • 16

• • 18

• 19

LOCATION1

Sotano de las Golondrinas is lo­cated in the east-central portion ofMexico in the southeast corner ofthe state of San Luis Potos{ (lat 210

36'N.; long 99 0 06'W.). This un­usual pit has forrned deep in theheart of the Sierra Madre Oriental,a rugged range of mountains extend­ing north into the Big Bend area ofTexas, U. S. A. and south, far intothe state of Veracruz. To the easta low coastal plain contrasts sharp­ly with the high mountains, while tothe west the Central Plateau is only3000 feet lower than the 9000 foothigh peaks of the range.

The only town in the Golondrinasarea that is acces sible by motor ve­hicle is Aquismon (see Geology sec­tion, page fig. 2). It is locatedat the eastern base of the SierraMadre, 51 km by road south of Ciu­dad Valles, S. L. p. Aquismon, thecommercial and political center ofthe area, is reached by a shortpaved road leading west from High­way 85, the Inter-American Highway.All travel west of Aquismon is byfoot or horseback on a network oftrails that interconnect all inhabitedplaces. These trails are often steepand rocky, though all main trailsare traveled by pack animals. Lackof dependable surface water limitssettlements to a few areas. In theseareas fields are cleared by cuttingand burning; corn is then planted onwhat soil may be found. Coffee isgrown extensively, and there aresmall fields of sugar cane. Thewestern part of the Golondrinas areais highe r and drier, with hardwoods,and at higher elevations, pines; inthe lower, more humid area to theeast the vegetation is more variedand tropical.

Permis s ion to enter Sotano de

las Golondrinas must be obtainedin writing in the form of a letter ofintroduction from the Presidente ofthe Municipio de Aquismon, whoseoffice is located in the building onthe nor t h side of the square inAquismon. Identification indicatingaffiliation with a univer sity or otherinstitution of higher learning usual­ly expedites matter s. After an in­troductory letter is secured,arrangements for the hi k e westmust be made. In the past cavershave customarily carried their per­sonalgear and hired a local guide tocarry the climbing ropes. Fifteenpesos a day is considered a fairwage for this service. Mules mayalso be hired to carry equipment.They rent for 20 pesos each per dayand a guide who cares for them isnormally paid 15 pesos per day.

The main trail to all points westbegins its steep climb immediatelyat the edge of Aquismon. Followingthis trail one must surmount twomountain ranges, cross two valleys,and partially ascend a third range.At this point the village of Tamapatzis reached, approximately 11 kmfrom Aquismon. It is absolutely es­sential that all cavers go directly toTamapatz where they must presentthe letter of introduction to the JuezAuxiliar. Official permis sion to ex­plore caves in the area will be ac­knowledged, and any aid or direc­tions the caver may need will be en­thusiastically given. From Tama­patz it is a 4 km hike northwest toGolondrinas. The entrance is some­what obscured by dense tropical ve­getation, but the people of the areaare very helpful in giving directions.

Before entering the Golondrinasarea, the caver should be aware ofsome of the conditions that exist.

2

Hiking is very exhausting for thosenot accustoITIed to it. The teITIper­ature is frequently above 90 degreesand high hUITIidity prevails. A hatand salt are necessary. When cav­ing between June and SepteITIber (therainy season) heavy daily showersshould be expected. CaITIping ispos sible in unus ed fields and occa­sionally in shelter s. PerITIis sionITIust always be obtained. It goes

without saying that all cavers ITIustrespect the local custOITIS and al­ways r eITIain courteous and polite.The caving potential of the ar ea istoo great to allow avoidable inci­dents to jeopardize public relations.In order to keep Mexican caving ona firITI basis and to insure that yourgroup will have the latest informa­tion on the caves of an area, contactthe AMCS when planning a trip.

CAVE DESCRIPTION and SPELEOGENESIS 3

Sotano de las Golondrinas (Pitof the Swallows) lies near the east­ern base of the Sierra de Union (seeGeology section, page 8, fig. 2) atan elevation of about 2400 feet (740meter s). The local people appliedthis name because of the tens ofthousands of swallows that inhabitthe pit. Seeing the swallows andthe beautiful green parrots slowlycircling as much as a thousand feetbelow the entrance is a breathtakingsight.

The nearly circular entrance ison a steep mountainside and has 109feet (33.2 m) of relief. It measures205 feet (62.5 m) by 160 feet (48.8 m)and is surrounded on three sides bytrees and dense undergrowth. Thelowest side is a barren ar ea of kar­ren cris scrossed by many narrowfis sures up to 15 feet deep. Only onthe low side is it convenient to rigthe pit.

In1967 when Sotano de las Golon­drinas was explor ed and mapped, itwas (and perhaps still is) the deepestfree-fall pit and the largest shaftknown in the world. Because of theimportance of the pit, a plane tableand telescopic alidade were used forsurveying and a wire with negligiblestretch employed for measuring thevertical drop. The walls of the pitbell out rapidly, giving a free dropat any point around the entrance. Asmay be seen on the map, the short­est pos sible drop is 1091 feet (332. 5m) free-fall. The usual riggingpoint is 1094 feet (333.5 m) above thefloor and the maximum drop is 1235feet (376.4m) free-fall. These mea­surements have a little more mean­ing when one realizes that the EmpireState Building would easily fit intothis sotano and its top would be aboutlevel with the high side of the ent­rance.

When one looks over the edge,the shape of the pit presents an op­tical illusion such that the wallslook nearly vertical and the floorseems not much larger than the en­trance ar ea. Only when one has rap­pelled several hundred feet does thepit corne into its proper per spective.Reaching the bottom is like enteringanother world. The nearest wall is200 feet away. After heavy rainssmall waterfalls pour from openingsa thousand feet above. During theday no artificial light is neces sarybecause of the large amount of sun­light that enter s the pit. Becaus eGolondrinas is located south of theTropic of Cancer, a beam of sunlightshines directly on the floor for sev­eral hours a day during the summermonths, causing a curious phenom­enon. Sunlight warms up the guano­covered floor and a cloud sever alhundred feet high forms, slowlyos­cillating up and down (see Photo­graphs, fig. 6). The floor has anarea of about 6 acres, a little morethan the average city block, and is1000 feet (304.8 m) long by 440 (134.1m) wide. Weathered guano and scat­tered breakdown co v e r the entirefloor. In places the guano (from theswallows) is several feet thick. Thebottom has 246 feet (75.0 m) of re­lief, with several hills ofbreakdown,intermittent streams, and a deeptrough along the south wall. Thelowest point in the cave lies in thetrough and is 1306 feet (398.1 m) be­low the entrance.

The origin of Sotano de las Go­londrinas is not yet fully understood.The factor s controlling the localiza­tion of the pit and their r elative im­portance cannot be evaluated withoutm 0 r e information. A n extremelylarge quantity of unsaturated waterhad to be supplied to produce such

4

an imITlens e chamber. Cons idering

the shaft as a truncated elliptic cone,the volume 0 f the pr es ent void isabout 200 million cubic feet (6 millioncubic meter s), or five times the vol­urn e of the well-known Gruta delPalmito (Bustamante, Nuevo Leon).Golondrinas, Hoya de Guaguas, andSotano de Cepilla--the largest knownpits of the area--are all developedalong prominent fractures. Golon­drinas is elongated parallel to a setof northwest-trending fractures thatmay be related to the thrust faultand fold west of the pit (see RegionalGeology). The straightnes s of thesouth wall in plan view and the 500foot sheer wall in section B-B' ofthe cave map are controlled by thesejoints. Two passages of sectionA_A' in the west wall are developedalong the most prominent fracturesand ar e unexplor ed.

Evidently, Sotano de las Golori­drinas was formed by: 1) develop­ment of a large phreatic rOOITl, and2) collapse of ceiling and wall rock.The floor of the shaft is composedentirely of breakdown and guano, andis 225 to 275 meters above the near­est resurgences, 15 km away. It islikely that the bedrock floor of thephreatic chamber is two or threehundred feet or more below the low­est point in the cave, and the wallsmay have extended upward to thepresent breakdown surface or evenabove it. Collapse of wall and ceil­ing rock began when the roof becameunstable, and proceeded slowly untilthe surface was intersected. Themajor joint set and per col at i n gg r 0 un d water undoubtedly greatlyassisted the collapse process. Thefragmented limestone that collectedat the bottom could readily be dis­solved if the water chemistry wasappropriate, because of the increas ein limestone surface area. Prob-

ably the top 800 feet or more of thepit has been forITled by collapse asindicated by the shape of the pit andthe lack of solutional featur es.

Pre sen t day modifications ofGolondrinas are proceeding slowly.Surface drainage does not directlyenter the pit and was not a factor inits formation. Guano, ITlinor quan­tities of flowstone, and sITlall piecesof breakdown below the entrance(from plant root wedging) are beingadded to the cave, but the rate ofaccumulation is very slow. A sITlallwaterfall is sues froITl the lower pas­sage on the west wall and usuallysinks quickly in the breakdown afterdepositing some calcite. Followingheavy rains water runs across thefloor and sinks in gravel and ITlud inthe deep trough along the south wall.o the r s ITlall str earn channels ar efound in the cave, which indicatesthat at t i ITl e s small s pr ings pourinto the cave and SOITle erosion oc­cur s . The floor of the alcove in thewest wall has been eroded by waterflowing into a tiny hole, leaving aprominent ridge in the breakdownand guano. It is quite likely that thepit is being deepened by subsurfacesolution of breakdown and gradualsubsidence 0 r slumping. ReITlovalhas apparently bee n concentratedalong the south wall, producing thelarge trough and a 60 foot cliff ofrecemented breakdown. For sub­surface solution of breakdown to beimp 0 r tan t, a 1 a r g e quantity ofgroundwater w 0 u 1 d be required toflow through the old phr eatic cham­ber, sin c e the waterfalls provideonly a minor amount of water.

Sotano de Cepilla, near Tama­patz, presents a history siITlilar tothat hypothesized for Golondrinas.The walls recede sharply froITl thesmall entrance to for m a pit 300feet in diameter and nearly 500 feet

deep at the lowest point. One wallofthe pit is composed of recementedbreakdown, which is now collapsing.About one-third of the floor is cov­ered by active flowstone depositedfrom waterfalls, and calcite is form­ing in a I a k e at the bottom. Therest of the floor is covered by break­down and conglomerate (from thewall of conglomerate). In a low por­tion of the floor much of the break­down is "rotten" becaus e of solutionand the floor appears to be subsid­ing due to subsurface solution.

Thus, the 1 a r g e pit s in theGolondrinas area have had a historycharacterized by development of a

large, deep phreatic chamber ands top i n g of ceiling and wall rock.When there has been extensive solu­t ion 0 f the breakdown by ground­water a deep pit has formed. Prob­ably the same fractures that domi­nate the shape of the pits also con­trolled the groundwater flow throughthe deep phreatic rooms when theywere formed. Although the detailedsol uti 0 n chemistry and hydrologyhave not been worked out. it appearsthat Golondrinas may be deepeningbecaus e of solution of the breakdownby w ate r flowing through the oldphreatic chamber and causing sub­s equent subsidence.

5

6REGIONAL GEOLOGY

INTRODUCTION STRATIGRAPHY

Regional Relations

The stratigraphy of the Golon­drinas ar ea is dominated by thet hie k accumulation of Cretaceouslimestones. Thes e rocks were de­posited in lagoons that border ed thesea during Cretaceous time, wherethe deposition of sediment kept pacewith subsidence to form s eve r a 1thousand feet of limestone. Most ofthis sediment was deposited as limemud in relatively deep water, but inshallow areas, sediment was deriv­ed directly from shell reefs. Thesereefs were not large solid bodies,but were unconsolidated shellmounds, the individual shell "reefs"being only a few hundred meterslong. Together with the much lar­ger volume of inter-reef sediment,they formed large calcareous banks,several of which have been named.To the northeast of the Golondrinasarea was the ElAbra Bank that bor­der ed the dee p water to the east.This bank had a relatively largeamount of reef material and nowforms the £1 Abra Formation thatis exposed along the eastern edge ofthe Sierra Madre Oriental. South­west of this bank and very similarto it were the Jacala and SierraLadron banks. These two banks,tog e the r with numerous smallerbanks, now form the £1 Doctor For­mation that extends throughout theSierra Madre from Cd. Victoria toPachuca. During late Cretaceous

Sotano de las Golondrinas lies inone of the lar gest and best developed}vlexican karst regions. In an areaof over 500 square kilometer s fromXilitla north to the RIO Santa Marfa,solutional processes have shapedthe landscape and surface drainageis absent. The southern part of thear ea is a high mountainous plateauwith peaks extending to elevations ofover 2900 meters. This high areais separated from the lower rangesto the north by an east-west solu­tional valley.

The Golondrinas region of thisreport lie sin the topographicallylower northern ar ea and extendsfrom Aquismon on the east to theSan Luis Potosl-Quer etaro borderon the we s t, and from Tampaxalnorth to Tansosob (fig. 2). Thisar ea, while mountainous, is lowerand less rugged than the high areato the south. Elevations range fromless than lOOmeters above sea levelin the lowlands east of Aquismon toover 1100 meter s at Cerro el Mira­dor 10 km to the southwest. Threesubparallel ranges cross the area:The S i err a de Aquismon and theSierra de Linja in the east, and theSierra de Union in the west. 1 Sepa­rating these ranges are relativelyflat sinkhole-pitted lowlands. Theentire drainage of the area west ofthe Sierra de Aquismon is under­ground, and wit h the exception ofsmall local areas, there is no evi­dence of any mechanical erosion-­even short gullies are abs ent.

1 The Sierra de Linja is also known as the Sierra de Manja, and in thesouth as the Sierra de Eureka; the name Sierra de Union is us ed principal­1 yin the vicinity of the barrio of Union, and locally the range is alsocalled the Sierra de Tamapatz, the Sierra de Mirador, and the Sierra deSan Rafael.

7

time large amounts of clastic sed'­ments, carried into the area fromthe west, killed and buried the reefs.These sediments now form the AguaNueva, San Felipe, and Mendez For­mations. The relation between theformations is indicated in Figure 1,a generalized east-west cross sec­tion showing the formations as theyexisted at the close of the Creta­ceous.

Cretaceous System

The base of the Cretaceous isnot exposed in the Golondrinas area,but lower Cretaceous limestone ofthe Lower Tamaulipas and OtatesFormations probably underlie muchof the area. These formations arenot present to the west where the ElDoctor lies dir ectly on the Juras sic,but they are exposed south of Xilitlaand north near Cd. Victoria.

Jurassic System

Rocks of Juras sic age are notexposed in the Golondrinas area, butare exposed to the south and westand probably un de r li e the Creta­ceous in the area. Thirty kilome­ters to the west, near Jalpan, thethin-bedded impure limestone andblack shale 0 f the upper Juras sicLas Trancas Formation directly un­derlies the El Doctor Limestone(Seger strom, 1961). To the south inthe canyon of the Rfo Moctezuma,rocks of the bame nature grade up­ward into cherty thin-bedded lime­stone that underlies the Cretaceousmassive limestones (Heim, 1940).

El Doctor Limestone. The El Doc­tor is the oldest formation exposedin the area and is by far the mostwidely occurring rock unit. In theGolondrinas area the El Doctor isprobably 600 to 700 meter s thick,thinning to the south but thickeningto the southwest toward the JacalaBank. The base of the forITlation isnot exposed and it is not possible todetermine accurately the local thick­ness of this ur:it. Segerstrom (1961)has estimated this formation to bealmost 1000 meter s thick in the Ja­cala Bank 30 km southwest of Go­londrinas. Heim (1940) gives thethickness of the El Doctor at Xilitlaas at least 400 meter sand thicken-

--- ---------M~E~N~DE=Z--~SlIl.tJRlt.FA&C<.t.E------------

OTATES

TAMAULIPAS

AGUA NUEVA

SAN FELIPE

LOWER TAMAULIPAS

AGUA NUEVA

EL DOCTOR

XlliTLA

___ - ----------::::::;:::::::;;s=::::::::::----- _---SOYATAL

____ ~EXCA~------....:..-----7"""

WESTGOLONDRINAS

AREA EAST

Figure 1. East-west eros s section showing the formations of theGolondrinas area and their equivalents at the close of the Cretaceous.

Contour Interval 100 metersTopoQrophic Bo.e, Volle. Sheel, 140-e(2), Mexico LlOO,OOO

a 2:3! !

KILOMETERS

4I

--,

GEOLOGIC MAP OF THE GOLONDRINAS AREA

SAN LUIS POTOSI. MEXICO

EXPLANATION

SEDIMENTARY ROCKS

~ Mendez Formation

en6 ~ San Felipe FormationWU<t~ Ague Nuevo FormatIona::u I:RI EI Doclor L,m.slone

• AdministrativeCobecero

Cenler

• Town Pueblo

0Ranch,do

Hamlet Barrio

Rood TTT EdQe of thrust sheet

Main trail Contact

Stole boundary T SIrike and dip

-+- Anticline -"t SIrik. and dipof overturned be ds

---t+ Plunging anticline X. Cove or pit

Figure 2

SIERRA DE UNION

250

750

1000

500

A

NORTHEAST

SIERRA DE AQUISMONSIERRA DE LINJA

La

KILOMETERS

o I 2 3 4 54' ; " ; ; I

Ked....

""';''' ".......... J

I

1000

til 750-1 Keda::ILl....ILl~

~ 500zQIi"ILl...JILl 250

Vertical EXac;)1l8ration 3.3 x

0SOUTHWEST

A

CROSS SECTION FROM AQUISMON SOUTHWEST THROUGH EL MIRADORFigure 3

10

ing to the north. Over 500 meter sof undisturbed El Doctor is exposed

in the canyon of the Rlo Santa Marla12 km north of Sotano de las Golon­drinas. Within the Golondrinas re­gion, the thickest expos ed section isin and above Sotano de las Golondri­nas, where over 500 meters of theEl Doctor is present.

The El Doctor Limestone of theGolondrinas area is a thick-bedded,light gray limestone, with beds us­ually from 1 to 2 meter s thick, al­though in several places there arezones where beds range from 10 to30 centimeters thick. A prominentzone of thin-bedded flaggy limestonewith beds averaging about 15 centi­meter s thick is expos ed from southof Tamapatz to north of Tansosoband forms the uppermost 50 meter sof the El Doctor. The thick-beddedzones tend to form extensive areasof lapies, with pinnacles 1 to 3 me­ters in height, and frequently cross­ed by deep, solutionally wid e nedjoints.

The El Doctor Lim est 0 n e iscompos ed of several different faciesthat interfinger in a complex rela­tionship. Near reef cores the bed­ding is commonly indistinct, whilethe thin-bedded zones generally re­present inter-reef areas. Becausethe reefs themselves are only a fewhundred meters in length and a fewtens of meter s t hie k, the type oflimestone and the bedding can varygreatly over a short distance. Asyet it is not known if solution favorsone facies or type of limestone, butit appear s that in the Golondrinasarea, fracturing plays a more im­portant role in cavern developmentthan variations in the primary po­rosity.

Agua Nueva Formation. Overlyingthe El Doctor in the western part ofthe Golondrinas area is the Agua

Nueva Formation. In this area thecontact is gradational, with the thin­bedded upper El Doctor grading up­ward through a zone of about 10 me­ters in to a flaggy, more argilla­ceous limestone with shale and silt­stone interbeds that forms the lowerAgua Nueva Formation. Approxi­mately 300 meters 0 f the A g u aNueva are exposed in the vicinity ofTamapatz. Near Tamapatz the thin­bedded flaggy gray limestones andinterbedded marls of the basal AguaNueva grade upward into a moreter rigenous unit about 2 00 meter sthick. This is overlain by about 50meter s of light gray medium-beddedlimestone with numerous thin no­dules of black chert. The AguaNueva is exposed in a belt extendingfrom 3 km south of Tamapatz tonorth beyond Tansosob and out ofthe area investigated. This narrowbelt averages about 800 meters inwidth and is over 10 km long. Theup per Agua Nueva, if present, iscovered by an overthrust block 0 fEl Doctor Limestone.

The Agua Nueva Formation hashad an important effect on the s et­tlement of the Golondrinas area,since it is an aquifer from whichn u mer 0 us springs rise. Thesesprings provide permanent w ate rfor a line of settlements along theoutcrop from Tamapatz to Tanso­sob. In addition the concentratedrunoff from the Agua Nueva has alsoformed several large caves whereit reaches the soluble El DoctorLimestone.

San Felipe Formation. The San Fe­lipe Formation is exposed in a nar­row band along the eastern slope ofthe Sierra de Aquismon. In the vi­cinity of Aquismon the formation isoverturned and the lower part cov­ered by an overthrust block of ElDoctor Limestone. The upper San

Felipe in the AquisIllon ar ea is athin-bedded, yellow-brown argilla­ceous liIllestonc with generally thin­ner interbeds of yellow shales. Theboundary between the San Felipe andthe overlying Mendez Forlllation isdrawn where the flaggy liIllestonesreplace the obscurely bedded Illarlyshales 0 f the Mendez For Illation.The contact is gradational through azone of about 15 Illeter s. Accordingto HeiIll (1940) this formation over­lies the El Doctor in the AquisIllonarea, the Agua Nueva being absent(fig. 1).

Mendez For Illation. Stratigraphi­cally above the San Felipe is theMendez For Illation. In the Aquis­Illon area it is generally a gr eenish,shaley Illarl with indistinct bedding.Only a slllall part of the thick Men­dez Forlllation is exposed in theGolondrinas area, where this rela­tively soft forlllation forllls the low­lands east of AquisIllon along theInter-AIllerican Highway.

STRUCTURE

Regional Structure

The structur e of the Golondrinasarea is dOlllinated by three Illajorelelllents: tl:e overt] rust and asso­ciated overturned anticline forlllingthe Sierra de Aqu ~ Lion along theeast edge of the areCI.; the cOlllplexanticline that fJrr:"1s the Sierra deLinja; and the overthrust forlllingthe Sierra de Union just west of s6­tano de las Golondrinas (fig. 3). Allof these strt'c~ures a:-" roughly pa­rallel. They trend to the north inthe southern ~art of the area andthen curve to the northwest in abroad arc. These structures endjust to the south of the area Illapped,

11

in the cast-west TaIllpaxal Valleythat is probably forllled along a Illa­jor strike-slip (tear) fault dividingthe structures of the Golondrinasarea frolll those of the Xilitla areato the south. Evidence for the faultis indir ect: the anticlines Clnd thrustsheets south of the valley do notIllatch thos e to the north, and thesouthern end of the structures tothe north of the valley are curved tothe we s t, probably by drag. Thegeologic Illap of HeiIll (1940) showsfour closely spaced thrust faults inthe valley near TaIllpaxal, indicat­ing that this area is structurallycOlllplex.

North of the Golondrinas areaare two sets of anticlines, the Illainset following the priIllary north­south alignlllent of the SierraMadr e, and the other for Illing asecondary set of northwest-trendingranges. These two sets of struc­tur e sinter sect in the Golondr inasar ea. The tectcnic stres s introduc­ed by the LaraIllide Orogeny at theclose of the Cretaceous, cOlllbinedwith the ]Jl.stic nature of the Men­dez Forlllation, resulted in theoverturned folds and thrust sheetspresent in the Golondrinas area.

Sierra de Aquis:mon

In the vicinity of AquisIllon the:rest of this range is forrned by anovertLr'l st block of El Doctor LiIlle­st.one. The cast edge of the lillle­stone forllls a prolllinent cJ i ff stand­ing above the relatively ~oft liIlle­stcnes and Inarls of the ~'an FelipeForrr,2tion. The San Felipe is over­~urned and dips 20 to 40 cegrees tothe west under the El Doct,w. Therocks exposed along the e as t ernslope of tr.e Sierra de AquisIllC:l. a:;'ethe east liIllb of an anticline over­turned to the east. To the south. the

12.

overthrusting and folding diminish,and in the southern part of the areathe Sierra de Aquismon is an anti­cline with a steepened east face, theEl Doctor dipping steeply to the eastunder the San Felipe. Nor t h ofAquismon the range continues as anoverthrust beyond the mapped area.

Sierra de Linja

This range is a complex asym­metric anticline that roughly paral­lels the Sierra de Aquismon to thewest. Like many other anticlinesof the southern Sierra Madre, it hasa steep east face and a gentler westslope. The range is composed ofseveral distinct smaller anticlinesthat plunge sharply to form narrowpasses in the range. In the passtraversed by the Aquismon-Tama­patz trail the axis of the anticline tothe south plunges north at 30 de­grees and the anticline to the northplunges to the south at 70 degrees.The sharp break where these struc­tures meet forms a narrow east­west valley. A sequence of similarsteeply plunging 10 cal anticlinescontinues to wher e the range diesout just north of the mapped area.

WEST

To the south the range merges withthe Sierra de Aquismon to form abroad anticline.

Sierra de Union

The Sierra de Union is the mostprominent range in the area and ex­tends as an unbroken cliff from Ta­mapatz north to San Rafael. Thiscliff is the east edge of an over­thrust block of limestone and standsover a narrow, frequently talus­covered outcrop of the west-dippingAgua Nueva Formation. The over­thrust continues north of Tansosobbut has little topographic expres­sion. From just north of Tamapatzand continuing south for about 2 kmis a vall e y developed along thestrike of the Agua Nueva. This val­ley drains to the west into c a v e sand sinkholes in the El Doctor (fig.4). One of the larger of the s ecaves, Cueva de Oxtalja, just westof Tamapatz, has developed alongthe plane of the overthrust. Thislar ge cave has a ceiling of mas siveEl Doctor Limestone and the floorand walls ar e in most places devel­oped on the crumpled and contortedthin-bedded Agua Nueva beneath the

EAST

Figure 4. Section B-B' through valley north of Tamapatz.

thrust sheet. The cave follows theplane of the overthrust for about onekiloITleter to the west; thus, the EIDoctor in this area ITlust have beenthrust at least this far to the east.The dip of the plane of overthrustwas ITleasured in several places. Inthe cave, Cueva de Oxtalja, the dipaveraged 23 degrees to the west,and one-half kiloITleter north of Ta­ITlapatz the dip was about 25 de­grees. In an excellent exposure inthe valley just to the west of Tanso­sob the dip was ITleasured to be 22degrees. In both the S i err a deAquisITlon and the Sierra de Unionthe beds in the EI Doctor dip steep­ly to the west near the east edge ofthe overthrusts, but within a fewhundred ITleters dip only gently tothe west. West of the Sierra deUnion ar e sever al nor t h - sou t hstructural trends that ITl a y repre­sent additional thrust faults, but asonly the ITlassive EI Doctor LiITle­stone is involved, the exact rela­tions are difficult to deterITline.

Minor Structures

Associated with these largerstructures are nUITlerous sITlallfolds. Several very tight folds areex po sed northwest of AquisITlon,where beds of the San Felipe arebent back upon theITlselves in lessthan a foot. CruITlpling and chevronfolding are also present in the thin­bedded upper unit of the El Doctorsouth of TaITlapatz. The thin-beddedAgua Nueva is cOITlplexly folded andcruITlpled beneath the overthrust ElDoctor. This drag folding is expos­ed in Cueva de Oxtalja as well as inthe hills capped by EI Doctor justnorth of TaITlapatz (fig. 4).

13

GEOMORPHOLOGY

Corrasional LandforITls

Although ITlost of the Golondrinasar ea is underlain by fractured liITle­stone, and solution is the dOITlinantprocess in shaping the landscape,there are a few areas where solu­tion is not iITlportant. East ofAquisITlon in the wide valley follow­ed by the Inter-AITlerican Highway,the soft Mendez ITlarl has been re­duced to a ITlature topography withonly a few rounded hills breakingthe gentle slopes. The steep out­crop of the San Felipe along the eastface of the Sierra de AquisITlon isdeeply gullied by erosion that is un­derITlining the cliff of El Doctor thatstands above the outcrop. The bandof Agua Nueva along the east side ofthe Sierra de Union is s i ITl i 1 a r,though 1 e s s gullied. The closedvalley along the strike of the AguaNueva west of TaITlapatz was pro­duced by corrasion; the erosion byITlechanical ITleans of the soft AguaNueva is apparently ITlore rapid thanthe solution of the surrounding ElDoctor.

Karst

Solution of the El Doctor LiITle­stone in the Golondrinas ar ea hasproduced a wide variety of land­forITls. The effect of solution iscontrolled by local conditions, pri­ITlarily the natur e of the liITlestone,rainfall, and local relief, all ofwhich vary widely acros s the area.In the valley to the west of the Si­erra de AquisITlon there is little ef­fective local relief. Here the sink­holes are shallow and poorly drain­ed. After eight days of rain duringSepteITlber of 1967 sinkholes in this

14

area were filled with water to

depths of over 10 meters. Watercompletely blocked the m a i n trailto Tamapatz and required severaldays to infiltrate into the limestone.T his entir e valley i s a ppar entlybeing lowered by solution. Solu­tional re sidue collects in the lowerdepressions and the local relief isnot enough to maintain open drain­age channels. The valley to thewest of the Sierra de Linja is simi­lar, though sinkholes are somewhatbetter developed and there is morelocal relief. However, the ar ea isstill comparatively flat, with thesinkholes covering only a smallportion of the surface.

In the higher ar eas west of theSierra de Union and south and westof Tamapatz, a much more spectac­ular type of k a r s t has developed.Her e there is much greater localrelief, and large elliptical sinkholesfrequently 0 vel' half a kilometerlong and one to two hundred meter sdeep cover the entire sur fa c e.These sinkholes are separated bysharp narrow divides a~1.d there islittle level land. Karren is commonand haystack hills have developed inthe more fractured areas. Furtherto the west the sinkholes tend to be­come larger and more elongate,with flat floors thinly covered withred clay. The largest of these isthe La Parada valley, just to thewest of the Golondrinas area. Thisflat-floor ed solution valley is 10 kmlong, 1 km wide, and up to 300 me­ters deep.

Caves and Pits

Considering the amount of rain­fall and limestone in the Golondri­nas area, caves and pits are not nu­merous. Apparently in much of thearea, solution has been so general

and channels for the descendingwater so plentiful that the entiresurface has been reduced by solu­tion. It appears that some mecha­nism is needed to concentrate thewater to have rapid development oflarge caves. No caves are known inthe poorly drained lowlands imme­diately to the west of the Sier ra deAquismon. In the wide valley to thewest of the Sierra de Linja twocaves are known. Satano de lasQuilas is a cir cular pit about 100meters deep and 80 meters in dia­meter. Cueva del Camino, 5 me­ters off the La Laja-Tamapatz trail,is alar ge pas sage about 100 meterslong with attractive formations.

Several lar ge caves exist alongthe mar gin of the Agua Nueva out­crop. To the south is Satano deMuhaut, a cave about 100 meterslong, and Cueva de Muhaut, whichhas been explor ed for about 300 me­ters and continues. Near Tamapatzis the large Cueva de Oxtalja thatreceives the drainage from an ex­tensive area. This cave is about1 km long and 200 meters dee p,though only two drops, one of 25meters and the other of 6 meters,require rope. North of this cave isCueva de San Nicolas, explored forone-half kilometer to a 30 meterdrop. North of San Rafael an unex­plored cave receives the runofffrom a long arroyo.

The most promising area forcaves appear s to be in the well-de­veloped karst southwest of Tama­patz. Several promising caves havebeen entered in this area, but noneof these have been explored formore than a few meters.

HYDROLOGY

It is not known where the large

amount of water that falls on theGolondrinas ar ea reappear s. TheGolondrinas area is about equidis­tant between the series of largesprings that forms the Rfo Huichi­huayan and the Nacimiento del RfoCoy. The headwaters of the RfoHuichihuayan ar e located about 15km to the south of the area, and theNacimiento del Rfo Coy is about 15km to the northeast. The Rfo Coyrises from a large spring (nacimi-

SELECTED

15

ento) at the end of an isolated lime­stone hill about 2 km long. Mo st ofthis water must flow under the in­tervening basin from the mountainsto the west. The m 0 s t 1 ike 1 ygroundwater divide is the Tampaxalvalley, just to the south of the Go­londrinas ar ea. If this is the dividethen the Golondrinas area rainfallreappear s at the Nacimiento del RfoCoy, 15 km away, at an elevation ofabout 50 meters.

REFERENCES

Bodenlos, A. F., anderra Madre en laGeol. Conf., 2 Oth,

Bonet, F., 1956, Notas sobr e la geologfa de la Si-. ,seCClon Zimapan-Tamazunchale: In InternationalMexico. Excursions A-14 and C-6, p. 293-309.

Bonet, Federico, 1953, Cuevas de la Sierra Madre en la region de Xilitla:Bol. Univ. Nac. Aut. Mex. Inst. Geol., 57, 96p.

, 1953, Biostratigraphic notes on the Cretaceous of East----------ern Mexico: In Corpus Christi Geological Society Eleventh AnnualField Trip, May 23-26, 1963, p. 36-48.

Corpus Christi Geological Society, 1963, Eleventh Annual Field Trip(Guidebook), Geology of Peregrina Canyon and Sierra de El Abra, May23-26, 1963, 90 p.

Cserna, Zoltan de, 1961, Tectonic map of Mexico; Geol. Soc. America.

Heim, Arnold, 1940, The front ranges of the Sierra Madre Oriental, Mex­ico, from Ciudad Victoria to Tamazunchale: Ec10gae Geologicae, vol.33, no. 2, p. 313-352.

Russell, William. H. and Raines, Terry W., 1967, Caves of the Inter­American Highway--Nuevo Laredo, Tamps. to Tamazunchale, S. L. P.:Asoc. Mex. Cave Studies, Bull. I, 126 p.

Segerstrom, Kenneth, 1956, Estratigraffa y tectonica del Cenozoico entreMexico, D. F. Y Zimapan, Hidalgo: In Internat. Geol. Cong., 20th,Mexico, Excursions A-3 and C-l, p. 11-12.

, 1961, Geology of the Bernal-Jalpan area, Queretaro,--~---------Mexico: U. S. Geol. Survey Bull. 1l04-B, 86 p.

Wilson, B. W.; Hernandez M., J. p. and Meave T., Edgardo, 1955, Unarrecife Cretacico en la parte oriental del Estado de Queretaro: Soc.Geol. Mex. Bol., vol. 18, p. 1-10.

16HISTORY

For at least 3000 yea r s theHuastecans, the or iginal settler s ofthe region, had k now n of the pit.They called it Xol Oclif. To theseIndians the large entrance and theimmediate surrounding area was ofno practical us e. It provided noplace to cultivate a field and fur­the r m 0 reconstituted a hazard,something to be avoided. T h us,little importance was given to thispit or the manyothers located in thearea.

When the Spanish fir st viewed it,they too attached little importanceto this natural feature. To them itwas known as Sotano de las Golon­drinas. The only interest eithergroup showed was for the swallowsthat inhabited the pit, and fromwhich the name was derived. Theyfound great sport in attempting tospear or shoot the birds.

Knowledge of Sotano de las Go­londrinas by organized explor ationgroups has not corne about until re­cently. The people of Tamapatz re­port that a group of six French andMexican mountain climbers went tothe entrance but did not descend.This was in 1957.

Then, during December of 1966,T. R. Evans, Charles Borland, andRanald Stearns, members of theAMCS and FTA (Fredrick Troglo­phyllic As sociation), were guided toGolondrinas. Lacking the propercaving equipment, they were unableto descend and had to satisfy theircuriosity by timing the fall of rocksand estimating the depth. At firstglance the drop appeared to be be­tween 300 and 400 feet deep. Bymeasuring the time that elapsed be­tween the dropping of a rock and thesound of it hitting the bottom, theyobtained a figure of 10 1/2 to 11 sec-

onds. From this they calculated a

depth of at least 800 feet.Only three months passed before

T. R. had organized a group to re­turn during the first week of April1967. Accompanying him were JonMorse, Sid West, and Bob Hugillfrom Ft. Detrick, Maryland; BillCuddington, John and Sandy Cole,and Dan Hale from Huntsville, Al­abama; and Squire Lewis, NancyWalters, and Bill Deane from Aus­tin, Texas. This time, possessingsufficient equipment, they succeed­ed in descending and exploring So­tano de las Golondrinas. Initially asingle rope was rigged and T. R.commenced what was to be a 30minute rappel. Later, three short­er ropes wer e joined to provide aline for prusiking. Using thes e tworoutes, eight member s of the expe­dition descended and returned to thesurface during the two day s thegroup was at the sotano. Three ofthem spent the intervening night onthe bottom. Most of the prusikingwas done the second day, the aver­age time on the rope being 2 to2 1/2 hours. The length of a nylonrope hanging from the rigging pointto the floor was noted and calcula­tions were made to allow for theamount of stretch. The resultingdepth of the drop (at the riggingpoint) was 1070 feet. Cons equently,Golondrinas bee arne the deepestknown free-fall pit in the world bya substantial mar gin.

The depth measurements obtain­ed from the April expedition wereadmittedly not extremely accuratedue to several variables. But twomonths later, during June, JohnFish, Ed Al e x a nd e r, JonathanDavis, Dick Mitchell, and Ted Pe­ter s returned with the purpose of

cOll1pleting an accurate survey ofthe entire cave. To accoll1plish thisthey us ed a plane table and tele­scopic alidade to survey the areasurrounding the entrance and thefloor of the pit, while the actualdrop was ll1easured with a steelwire 0 f little and known stretch.The surface survey, the rigging ofthe drop, and the ll1easur ell1ent withthe wir e r equir ed one day to COll1­plete, while another day was spenton the bottoll1 finishing the secondphase of the survey. The new fig­ures obtained were sOll1ewhat higherthan those of earlier date. Thelongest free-fall drop is 1235 feet,the shortest is 1091 feet, and a drop

17

of 1094 feet was ll1easured at therigging point. The total depth of thecave is 1306 feet. Now, certainly,the authenticity of the new world I srecord could not be questioned.

Since these early explorations,a large nUll1ber and variety ofgroups have visited t his aweSOll1esotano. The ll1ass pilgrill1age hasso aroused the interest and suspi­cion of the local residents that SOll1ebel i eve the strangers COll1e insearch of gold, oil, or other valu­able objects. Fortunately, the situ­ation has eased and as responsiblecaver s continue to visit the are a,public r elations will be establishedon a really first class level.

18EQUIPMENT Jnd TECHNIQUES

As is to be expected, cavingequipment and techniques vary fromone individual to another. Virtuallyall methods for ascending and des­cending a drop have been tried andtested during the past six years ofMexican caving. Through an evolu­tionary proces s, the more undesir­able means have been abandoned,until now one system predominates••• rappel and prusik.

Of primary importance to thesucces sful negotiation of a sotano isthe climbing rope. It is of nylon,varying in diameter from 3/8 inchto 1/2 inch. Either 7/16 inch or 1/2inch have been most widely us edbecaus e of the distasteful amount ofstretch and general weakness of 3/8inch rope. These ropes are eitherlaid or braided. In the cas e of Go­londrinas, braided rope was oncethought superior due to the absenceof spin while climbing. This wasdisproven when Goldline laid ropewas us ed and only negligible spinnoted. No matter what brand ofrope is used, great care should betaken to protect it against damagefrom sharp rocks.

The amount of equipment neces­sary for the rappel is not gr eat. Aseat sling with a locking carabineris us ed in conjunction with either aset of two oval carabiner s· and br eakbars, or a rappel rack as describedin the NSS NEWS,v. 24, n. 6, June1964. Both methods work well, theadvantage of the rappel rack beingthat less feeding is necessary at thebeginning of the rappel. If the rateof rappel is too rapid, the heat that

is generated will severely damagethe rope. Care should be taken notto exceed a rate of 40 feet per min­ute or stop at anyone point alongthe rope. A rappel of this magni­tude not only affects the equipmentbut also the explorer. Having asecond person pull up the climbingrope a few feet to produce enoughslack to allow the rappel device tobe attached is very helpful. Onceon the rope, it is advisable to movethe legs as much as possible be­cause during the 30 minute rappelthe seat sling restricts blood circu­lation.

In addition to a s eat sling, theprusik method requires only a setof two or three loops, depending onwhether one 0 r two feet are used.If Jumar Ascenders are used, thes eat sling loop is attached too n eJumar and either one 0 r two footloops are attached to the 0 the rJumar. The length of the drop to beascended does not affect the prusik­ing equipment, as it does the gearused in rappelling. The only limi­tation to the distance that it is pos­sible to prusik is the human energyfactor. In Golondrinas the averagetime required to prusik out is 2 to2 1/2 hours. On the other hand, thedistance that it is possible to rap­pel is limited to the ability of therappel device to deal with the weightof the climbing rope. As it appear snow, some new innovation or im­provement of the existing equipmentwill be needed when it becomes ne­cessary to descend a drop of morethan 2000 feet.

PHOTOGRAPHIC DESCRIPTIONS19

Figure 1. Aerial view of Aquismon, S. L. P. and surrounding mountains.This photograph was taken looking south down the valley followedby the Inter-American Highway. The right side of the photo showsthe eastern edge of the Golondrinas area, which is separated bythe Tampaxal Valley from the higher mountains (peaks over 2900meters) in the background. The trail to Tamapatz begins its as­cent at the north edge of Aquismon and crosses the first range in apas s just out of the lower right corner of the photo. The geologicfor mations are: valley floor - Mendez Formation; slope aboveAquismon - San Felipe Formation; and scarps and ridges to thewest - El Doctor Limestone.

Figure 2. Westward aerial view of Satano de las Golondrinas. The entranceis located near the base of the Sierra de Union and is quite promi­nent from the air. The main trail eros sing the center of the photoconnects Tamapatz and Tansosob. The 4 km hike from Tamapatzto the pit requires about 1 1/2 hours. The trail leading out of thelower left corner returns to La Laja and Aquisman. Just to thelower right of center three tro:tils meet at Pozo de Guadalupe, thewater supply of the local area. The geologic formations o:tre: Pozode Guadalupe and below - El Doctor Limestone; center cultivatedslope - Agua Nueva Formation; and upper cliffs - El Doctor thrustfront.

Figure 3. The entrance of Satano de las Golondrinas. This wide angle photo­graph shows the cornplete entrance with dense tropical vegetationsurrounding it on three sides. The surveyed high point of the en­trance :~s in the upper center above the cliff face, while the usualrigging point is in the middle of the group of people. When pre­paring the equipment prior to des cent, the rope must be unbraidedon the rough karren in upper for eground.

Figure 4. First exploration group. During April of 1967 the pit was first en­entered. Using 1/2 inch Samson 2 in 1 nylon rope (well padded),an explorer begins the 30 minute, 1094 foot free rappel to the bot­tom. The man with the white hard hat, clos est to the rappeller,uses a walkie-talkie to communicate with an explorer already onthe bottom. Extreme caution must be taken when approaching theentrance dne to the uneven, deeply fissured karren.

Figure 5. Descending into the pit. Although only about one-sixth of the wayto the bottom, the explorer is already approximately 150 to 200feet below the camera and the lip of the pit.

Figure 6. The entrance shaft. A small waterfall near the entrance shineswhite in the sunlight while the climbing rope (center) appearsdark. The beam of light warms the moist walls and floor, produc-

20

ing a cloud which oscillates up and down in the pit. The brokenappearence of the wall rock and absence of solutional features in­dicate that Satano de las Golondrinas was formed by stoping ofceiling and wall rock into a large solutional chamber.

Figure 7. Lengthwise view of bottom. The floor of Golondrinas is composedof medium to small weathered breakdown, deep guano, and somesilt. It measures 440 feet by 1000 feet and has an area of about6 acres. In this eastward view a person is standing in the centerof the photo for scale. Halfway between him and the left edge theclimbing rope is bar ely visible. The 40 foot long log in left centeris in the middle of the projected entrance area (see cave map).This area is lighter in color due to broken rock pieces. Thetrough in Figure 8 is down and to the right of this photo.

Figure 8. The trough. The lowest point in Golondrinas (1306 feet below theentrance) is located in the trough, seen here in this photo. It isin the shallow arroyo slightly back and to the left of the personstanding in lower center. The left wall of the trough is formed bythe pit wall, which is sheer for 500 feet. Steep slopes and a 60foot high cliff of breakdown with silt and guano matrix form theright wall. The cave at lower left extends only 15 feet and ends.In the upper right corner is a somewhat larger alcove (see cavemap).

Sotano de las Golondrinas

Color PhotographsFigures 1 through 8

PHOTOGRAPHY BY

TERRY w. RAINES and BILL DEANE

Figure 2

Figur 4

Figure 5

Figure 6

Figure 8