Robber Baron Cave Preserve

Preserve Manager: Joe Mitchell
Assistant Manager: Mike Harris

Robber Baron Open House 2019

The next Robber Baron Open House is scheduled for Saturday, September 28, 2019 from 9am to 3pm. This special event only occurs once every 18 months, so don’t miss this rare opportunity! The Open House is open to the public. It is

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Tours at the Robber Baron Open House

The Robber Baron Open House is Saturday, November 11, 2017 from 9:00 am to 3:00 pm and we hope you can attend! Even though advance reservations are now full, they are NOT required to take the regular self-guided tour to

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Robber Baron Open House 2017

The next Robber Baron Open House is scheduled for Saturday, November 11, 2017 from 9am to 3pm. This special event only occurs once every 18 months, so don’t miss this rare opportunity! The Open House is open to the public.

Read More »


Robber Baron Cave has been the site of numerous scientific studies, and Texas Cave Management Association continues to promotes cave and karst research at Robber Baron Cave Preserve. Its location in a major metropolitan area with easy access makes it an ideal site for research. As a karst resource, it has unique geological features and biological species, including endangered species that are found nowhere else.

Some of the scientific studies performed at Robber Baron Cave include:

  • 3D cave mapping prototypes (a partial 3D map of the cave has been done and printed in 3D).
  • Biological studies, including identifying two endangered species.
  • Edwards Aquifer studies, establishing a link between Robber Baron and the Edwards Aquifer.


Tricolored bats in the entrance room of Robber Baron Cave.

A large variety of species live in Robber Baron Cave, although most visitors might not notice them. The majority of the species in the cave are invertebrates, but in the last few years an increasing number of tricolored bats (Perimyotis subflavus) have been making the cave their home in the winter. These bats use the cave for hibernation and are known to return to the exact same spot to hibernate year after year.

Examples of invertebrates observed in the cave include:

  • beetles
  • spiders
  • harvestmen
  • pseudoscorpions
  • assassin bugs
  • cave crickets
  • centipedes
  • millipedes
  • silverfish
  • earthworms
  • cockroaches
  • mosquitoes
  • moths
  • flies
  • snails

These species can be largely divided into trogloxene, troglophile, and troglobite. A trogloxene enters a cave just for reasons of food, to escape summer heat, or to hibernate, but does not live there. A troglophile lives a portion of its life in a cave but also lives part of the time above ground. A troglobite, on the other hand, is so well adapted to the underground environment that it is only found in caves and does not survive well on the surface.

At least ten separate troglobitic species have been found in Robber Baron Cave. These include two species of isopods, two species of spiders, a harvestman species, two species of millipedes, one species of earwiglike entotrophs, a silverfish species, and an antloving beetle species. [1]

Endangered Species

In December 2000, two species in Robber Baron Cave were federally listed as Endangered Species (along with seven other troglobite invertebrate species in Bexar County). These are:

  • Cicurina baronia (Robber Baron Cave Spider, also known as Robber Baron Cave Meshweaver), and
  • Texella cokendolpheri (Robber Baron Cave Harvestman, also known as Cokendolpher Cave Harvestman).

Both of these species have been observed only in Robber Baron Cave. They are very small in size, only a couple of millimeters, essentially eyeless, and mostly lacking in pigmentation. These species are well adapted to caves, having a low metabolism due to the lack of food, and long legs for efficient travel and to feel their surroundings.

Robber Baron Cave Spider (Cicurina baronia). Photo by Dr. Jean Krejca.

More information about endangered species in the Edwards Aquifer karst can be found here.


Robber Baron Cave is a maze cave with a complex set of interconnected passages that generally intersect at right angles. The cave is found within the Austin Chalk formation, which underlies most of north-central Bexar County. The Austin Chalk is one of the upper confining layers of the Edwards Aquifer and in the location of the cave, is an upthrown fault block. It is a soluble formation, meaning that water flowing through small cracks can, over long stretches of time, dissolve the rock (in contrast to physical erosion). Austin Chalk is also relatively soft and rather clay-like (and less soluble) in its upper layers.

It appears that the cave may have formed in two periods. The first one established the basic layout of passages. A second period followed after the cave opened to the surface, where runoff played a role in enlarging some passages, while partially filling others with sediments. [1]

Many features predicted by the hypogene speleogenesis theory are visible in this photo: cupola domes in the ceiling, narrow apertures, and slot-shaped passages. Photo by James Jasek.

There are several theories to explain the origin of the cave (its speleogenesis). One involves aggressive water flow near locations of constrictions in the main flow (floodwater mazes). Another states that slow and dispersed flow through an upper rock layer that is not soluble could form such caves (diffuse recharge). [2] Recently, a new theory has been proposed, known as hypogene speleogenesis, that explains maze caves as a result of ascending ground water. [3] In this theory, water from an underlying aquifer is hydraulically forced up into overlying beds of rock. The water then travels horizontally through fractures in this bed for long distances along multiple paths. If fractures that are differently oriented exist in the overlying bed, the water may be forced up into these and form crossing passages. Characteristic features of this theory are the presence of small orifice-like feeders, which are small rounded “ear canal” like openings in the floors of passages, along with cupolas, which appear as a series of small domes in the ceilings of these passages. Robber Baron was most likely formed by hypogene processes since it has numerous such feeders and cupolas and local conditions make the other theories unlikely. Recent studies have supported this theory with the ancient Edwards Aquifer being the probable source of the rising water about 2.0 to 2.5 million years ago. [4]


Robber Baron Cave maintains a near constant temperature of 71°F. Although this may sound pleasant, the relative humidity is near 100%, which leaves no place for sweat to evaporate. Airflow in this cave, as with most caves, is dependent on local barometric conditions. As air pressure falls (such as from a passing storm) the lower pressure outside will draw air out of the cave causing a breeze in passages toward the entrance. During periods of rising pressure, the reverse is true. Some small passages deep inside the cave also exhibit airflow indicating the presence of cave passages beyond that which are known.

One of the main features of the cave is the presence of significant amounts of carbon dioxide (CO2) at certain times, known as “bad air”. CO2 levels are also driven by barometric pressure changes. High pressure pushes fresh outside air into the cave, while low pressure pulls more CO2 from deeper portions of the cave and allows it to build up. [5] In general, the air quality is better in the winter months when more frequent pressure changes occur from cold fronts. Occasionally, when low pressure dominates for a period of time, some portions of the cave may be problematic to enter as the high CO2 levels can result in extreme shortness of breath, even when not moving, along with dizziness and disorientation (concentrations of more than 12,000 ppm have been measured in the cave.) These symptoms disappear quickly when returning to areas near the entrance (although a headache may remain when CO2 concentrations are especially high). One theory regarding the origin of the CO2 is that it may arise from chemical reactions of surface water with the surrounding rock, or alternatively, that it may be out-gassing from lower rock layers submerged within the aquifer. If this latter hypothesis is true, it would indicate connections to the aquifer in an area not usually considered part of the recharge zone, which has implications for San Antonio’s water quality. A recent study in the cave with a mass spectrometer have also measured similar levels of CO2 along with a corresponding decrease in oxygen (O2) levels. A detection of ammonia (NH3) may also have been made. [6]

Scientists from Southwest Research Institute and St. Mary’s University used a portable mass spectrometer to analyze the atmosphere in Robber Baron Cave and several other central Texas caves. Photo by Larry Walther, courtesy of Southwest Research Institute.


[1] Veni, G., The Caves of Bexar County, Speleological Monographs 2, Texas Memorial Museum, University of Texas at Austin, p. 300, 1988.

[2] Palmer, A. N., “The Origin of Maze Caves“, NSS Bulletin, v37, n3, pp. 57–76, July 1975.

[3] Klimchouk, A., Hypogene Spelelogenesis: Hydrological and Morphogenetic Perspective, National Cave and Karst Research Institute, Special Paper No. 1, p. 106, 2007.

[4] Veni, G., “Hypogenic Origin of Robber Baron Cave: Implications on the Evolution and Management of the Edwards Aquifer, Central Texas, USA”, Advances in Hypogene Karst Studies, NCKRI Symposium 1, pp. 85-97.

[5] Mitchell, J. N. and E. J. Mitchell. “Airflow and CO2 in Robber Baron Cave”, Proceedings of the 15th International Congress on Speleology, Kerrville, Texas, v3, pp. 1613-1619, Jul 2009.

[6] Patrick., E. L. et al., “A Prototype mass spectrometer for in situ analysis of cave atmospheres“, Review of Scientific Instruments, v83, n10, Oct 2012.

You can help Robber Baron Cave.

If you are interested in helping us protect and maintain this unique and special part of San Antonio, please consider joining Friends of Robber Baron or donating to TCMA to help maintain Robber Baron Cave Preserve.

Donations may be made online, or checks may be mailed to TCMA, P.O. Box 7427, Austin, TX 78713. Please indicate on the check that it is in support of Robber Baron Cave Preserve.