Enchanted Rock Cave

On the back side of the Enchanted Rock summit is a cave that’s nearly 1,000 feet long. This isn’t your typical stalagmite/stalactite formation, it’s more of a long rock tunnel through giant underground boulders. To find the main entrance climb to the top of Enchanted rock then identify the rock quarry far out in the distance to the Northwest. Using that as a guide, begin walking down the back side of the summit until you see a boulder field and a wooden sign marking the cave. All the way through and at the entrance are white arrows to guide the way. Near the end there is some orange writing and arrows that say “Dead” which means dead end. Take care when entering or exploring the cave during rainy weather, it may become slippery or even flash flooded.

Address:The trail head is located at 16710 Ranch Road 965, Fredericksburg, TX 78624, (800) 685-3636 entrance is $6 per adult (13 or over).
GPS Location: park entrance 30.496046, -98.819897 cave entrance 30.506538,-98.819232

Cave Details: Be sure to carry along a flashlight or headlamp. This cave can be managed using the light from a cell phone but it’s riskier and there are lots of drops and places where ankles or knees could be hurt. You can ask for a map of the cave at the entrance to the park but we managed fine using the white arrows mentioned above and were out in under an hour. There were a few spiders but in general the cave was very bug free.

Official Scientific Details: A very unusual cave has formed near the summit of Enchanted Rock. It is one of the largest caves known to have developed within an inselberg mass. The origin of the cave may be attributed to four processes: 1) Fracturing of the bedrock mass 2) Grussification 3) Removal of detritus of mechanical suffusion 4) Roofing by talus accumulation.

More than 300 meters of passageway have been surveyed and although there are over 20 entrances to the cave, there is one large passage, 70 meters long and 2 to 3 meters high, on a lower level where artificial light is necessary for exploration.

Fracture formation: A long, northeast fracture extends for approximately 500 meters parallel and near to the northwest face of the inselberg. The fracture formed prior to exhumation of the inselberg and Enchanted Rock cave later developed by weathering along this plane of weakness. The fracture is actually sheeting joint between the inselberg mass and a large exfoliating sheet forming the northwest face.

Grussification: Chemical attack on the fracture may have begun prior to erosional exhumation of the dome, as ground-water seepage infiltrated to the upper surface of rock mass. Chemical weathering of bedrock in contact with seepage water weakened the fracture wall rock considerably. Grussification has been most intense where the main fracture is intersected by another fracture of vertical orientation. Here the grus zone in the walls is greatest. Water seeping downward through the fractures eventually encountered unaltered rock where the fractures were still closed, and it was then forced to move downslope along the fracture of strike to the northeast. As exhumation of the dome progressed, removal of dissolved minerals, such as oxidized biotite and “chalked” plagioclase, became possible and seepage became more rapid. The fracture enlarged in width, especially in lower parts of the fracture where water became perched. Orthoclase and quartz grains were left behind as disaggregated grus to be removed later, largely through further dissolution and physical erosion.

A large bedrock basin developed on the dome surface adjacent to and southeast of the fracture concommittant with grussification along the plane of fracture. Beginning parhaps as a small gamma and enlarging upslope by chemical weathering and exfoliation along its periphery, this depression eventually attained a diameter of 20 meters. Runoff from a large area of the dome is concentrated by this amphitheatre-like pit and is channeled directly into the main fracture.

Mechanical suffosion: Disaggregated grus has been removed from the cave by mechanical suffusion. The cave has been, and still is, flushed periodically by catastrophic storms typical of the central Texas region. Further grussification by ponded water collecting on the cave floor following storms has further weathered the adjacent bedrock. Spalling and erosion have enlarged the fracture width to enterable dimensions forming Enchanted Rock Cave.

Roofing by talus accumulation: Enlargement of the host fracture has progressed substantially to allow breakup of the upper fracture walls. Large granite blocks, weathered out along smaller joints and fractures, have been dislodged and displaced downward into the fracture. In addition, some slabs of exfoliated sheets from the steep northwest dome surface accumulated within the fracture, sealing many of the interstices among larger blocks and roofing large sections of the cave.

Weakening of bedrock by chemical weathering and removal of grus from the subsurface by dissolution and mechanical suffusion have enlarged a fracture to enterable dimensions. A unique relationship between this fracture and a contributive drainage basin on the dome surface has produced on the largest known granite caves.

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