Day Three: Into the Depths – Carlsbad Cavern, Parks Ranch Cave System, and Sitting Bull falls

 

Reference map for day three stops. Basemap sources: National Geographic Society and i-cubed (2013); Esri, TomTom, Garmin, FAO, NOAA, USGS, OpenStreetMap contributors, and the GIS User Community. Additional data: PermianBasin_Boundary_Structural_Tectonic. Map created by Brittney A. Hawley in ArcGIS Pro 

First Stop: Carlsbad Cavern 

Descending into Carlsbad Cavern feels like stepping onto another planet. The air grows cooler, the world above fades away, and you're enveloped by a subterranean realm of breathtaking scale and beauty. As someone who hasn't spent much time in caves, everything about this place was spectacular and awe-inspiring. We spent half the day exploring the cavern, and I could have easily spent the rest of the day wandering its passageways. There are countless fascinating geological features, each with its own story.

A closer look at Carlsbad Cavern’s wonders: here, stalagmites rising from the floor meet stalactites hanging from the ceiling, forming striking columns. Popcorn-like calcite textures cover the surfaces, adding a delicate, intricate detail to the formation.

The cave's history is rich and complex. It began with limestone deposition from Capitan Reef, and over time, water moving through folds and fractures dissolved the rock, carving out enormous caverns. Caves develop unique microenvironments, and within these spaces, different geological formations form depending on factors like dissolution, carbon dioxide degassing, convection currents, wind direction, water chemistry, and more.

Most caves form through the action of carbonic acid, but Carlsbad is unique: its passages were carved primarily by sulfuric acid. Hydrogen sulfide from nearby oil and gas deposits combined with groundwater and rainwater to produce this strong acid, which traveled along fracture planes, dissolving the limestone more aggressively than carbonic acid could. This process is why Carlsbad Cavern is so massive and also why it hosts impressive gypsum deposits. (National Park Service, 2025) Chemically: 

H₂SO₄ (Sulfuric acid) + CaCO₃ (Calcium carbonate/limestone) → CaSO₄·2H₂O (Gypsum) + CO₂ (Carbon dioxide)

Carlsbad Cavern is a vast network of over 100 limestone caves and passageways. One of the most remarkable features is the Big Room, the largest accessible cave chamber in North America. It measures approximately 4,000 feet long, 625 feet wide, and 255 feet high at its tallest point, and the floor space spans about 8.2 acres (Earthdate, 2023). 

I’ll take you on a geologic overview, sharing photos I took along the walk to the Big Room, along with geological context and history.

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Before even entering the cavern, take some time to explore the outcrops around the parking lot. Here, you can see an interesting teepee structure, a secondary diagenetic feature formed when water pushed upward, causing the limestone layers to buckle and fold. You’ll also notice small spherical carbonate grains called pisoids embedded in the rock. These form in shallow marine environments, where concentric layers of calcium carbonate build up around a nucleus, such as a shell fragment or a grain of sand. (Burger, 2007, p. 7)

 

A teepee structure in the limestone outcrop outside
 Carlsbad Caverns Visitor Center. Water pushed upward,
 buckling the layers and leaving this pseudo-anticline.

Spherical concentric concreting layers surrounding a nucleus, called a pisoid. These are about one cm in diameter 

The descent into the cave follows steep switchbacks. Once inside, take a moment to notice the smooth surface of the ceiling. This flatness is due to the Tansill Formation, which contains numerous clay layers interbedded with siltstone and dolomite. Over time, the weaker clay layers give way more easily than the surrounding rock, producing the cave’s smooth surfaces. In some areas, you can even see mud cracks preserved in the mudstone layers of the ceiling, which are polygonal patterns formed when the ancient lagoon environment repeatedly wet and dried. Shining your flashlight along the walls, you’ll also spot small gypsum deposits glinting in the light. (Burger, 2007, p. 8-9)

The natural entrance to Carlsbad Cavern cuts through the Capitan Reef limestone, exposing stratified Tansill Formation layers. 

A look at the cave ceiling showing polygonal mud cracks

Walking toward the Big Room, you’ll notice that many of the stalactites are asymmetrical. The mineral buildup occurs on the side facing the incoming airflow, the upwind side. This happens because moving air enhances carbon dioxide degassing from the thin film of water on the stalactite’s surface, which in turn promotes calcite precipitation and gradual growth in that direction. 

Asymmetrical stalacites forming on the upwind side

Along the trail, you’ll encounter a feature known as boneyard, a highly eroded limestone surface that resembles a honeycomb or sponge. This texture formed through sulfuric acid dissolution when hydrogen sulfide rising from deeper reservoirs mixed with groundwater. The resulting sulfuric acid aggressively dissolved the limestone of the Capitan Reef, enlarging fractures and bedding planes. Over time, this process created the irregular cavities and sharp ridges characteristic of the boneyard, representing one of the earliest stages of cave formation in Carlsbad Cavern. (Burger, 2007, p. 22)

Intricate honeycomb structure with many dissolved passages called boneyard

In the Big Room, one of the most eye-catching formations is the Lion’s Tail, named for its long, slender shape capped with knobby cave popcorn. This feature forms through convective air currents circulating within the cavern. The movement of air within the cave is driven by temperature and density differences between the large cave entrance and the underground chambers.  These convection currents move moisture and dissolved carbon dioxide throughout the cavern, influencing where calcite dissolves and re-precipitates. As the dry air moves down, it increases evaporation and allows the precipitation of aragonite and calcite popcorn. The warm air moving up and out of the cave carries moisture, and dissolves aragonite and calite. This is why you'll see a line on features where minerals have precipitated on the bottom, but the top will be smooth. (Burger, 2007, p. 24)  

Lions tail formation characterized by it smooth surface at the top and cave popcorn texture at the bottom

A few more interesting features include stone lily pads and pool fingers. Stony lily pads are a special type of shelf stone that reflects water levels in the cave pools. When the caves were dry, stalagmites would form on the ground surface. Then, water entered, and floating calcite crystals attached to the stalagmites as the water rose, creating these lily pad structures. Pool fingers are interesting because they have evidence of fossil bacteria. These are slender calcite structures that can be up to 30 cm in length and about 1.5-6 mm in diameter, and grew vertically under shelf stones in water. It is believed that bacteria contributed to the formation of these structures through microbial mediation or passive processes, and is a subject of much scientific debate. (Melim et al., 2001) 

Stone lily pads in an ancient cave pool — calcite shelves that formed as rising water levels allowed floating crystals to attach to submerged stalagmites. These structures record changes in past water levels within Carlsbad Cavern

Slender calcite pool fingers along the shelf stones of a former cave pool. These tube-like formations, up to 30 cm long, likely formed through microbially mediated precipitation of calcium carbonate within still, mineral-rich water (Melim et al., 2001)

These are just a handful of the incredible formations found in Carlsbad Cavern. Before your visit, I highly recommend reading about how these features formed. You’ll recognize them much more easily once you’re underground. On your way out of the cave via the elevator passage, take a moment to look closely at the surrounding walls. If you’re lucky, you might even spot fossil remains, like the trilobite our group found near the exit.

Fossilized trilobite embedded in the limestone wall near the Carlsbad Cavern elevator exit. These marine arthropods lived in the shallow seas that once covered this region during the late Paleozoic era

Second Stop: Parks Ranch Cave System

Carlsbad Cavern may be the most famous cave in the region, but the gypsum caves of the Parks Ranch Cave System are spectacular in their own right. Dissolution plays a major role in both cave systems, but the gypsum caves occur within the Artesia Group formations, specifically the Castile Formation. Because gypsum is more soluble than limestone, it produces an extensive network of maze-like tunnels.

Narrow gypsum passage within the Parks Ranch Cave System, showing sparkling crystalline gypsum formed by epigene dissolution

The primary process behind these caves is known as epigene gypsum karst. In this setting, rainwater percolates downward through soil and fractures in the Castile Formation, dissolving the gypsum along its path. Over time, this process creates sinkholes and horizontal passages. Since gypsum dissolves so readily, the Parks Ranch caves are constantly evolving and reshaping. (Stafford, 2013) 

Besides sinkholes, karrens are extensive across the gypsum plain’s outcrops. Inside the caves, you can often see scalloping on the walls, evidence of intense water flow that once moved through these narrow conduits. The passageways are completely entrenched in gypsum, and their white, crystalline walls glisten under light, giving the cave an almost sparkling appearance. In some areas, delicate varves of the Castile Formation are visible. 

Extensive scalloping on the walls of the lower Parks Ranch Cave, formed by turbulent water flow during periods of active gypsum dissolution

In the lower cave of the Parks Ranch system, I initially hesitated to go in because the entrance was so low that I had to crouch and duck to move forward. With all my classmates crowding the space, it felt too tight to enter comfortably. I decided to wait and then follow behind once they had gone ahead, which helped ease my claustrophobic feeling. After about 30 yards, the passage opened up enough for me to move comfortably and catch up with the group. It ended up being one of my favorite experiences of the field trip, an untouched slice of nature. 

Because these caves lie close to the surface, weather awareness is critical. If rain is expected within a few hours, it’s best to postpone any exploration. Rainwater infiltration can lead to hazardous flash-flooding conditions within the narrow passages. With nearly four miles of mapped passageways, Parks Ranch is the largest gypsum cave system in the United States, and planning your trip carefully is essential.

When visiting any undeveloped cave, safety must come first. It’s recommended to go with at least three other people and carry three backup light sources in addition to your headlamp. Basic protective gear: helmet, knee pads, elbow pads, and sturdy footwear is also a must for navigating the tight and often abrasive gypsum passages (Parks Ranch Cave, Carlsbad Field Office Recreational Caves, n.d.). 

Third Stop: Sitting Bull Falls 

Sitting Bull Falls is a scenic recreation area in the Lincoln National Forest, best known for its 150-foot waterfall that plunges into a deep, clear pool. The site is framed by steep cliffs composed of Permian-aged San Andres and Grayburg limestones, with Cherry Canyon sandstones on the lower slopes. These rocks are part of the same ancient carbonate platform and reef complex that built the Guadalupe Mountains during the Permian Period. (NMBGMR, 2020-b)

Our class making our way toward the waterfall, crossing one of the spring-fed pools at Sitting Bull Falls. Photo by: Kailey Warrior

Like at Rattlesnake Springs, the mineral-rich groundwater feeding Sitting Bull Falls flows through porous and cavernous limestone, and degasses as it reaches the surface, causing calcium carbonate (tufa) to precipitate. Over time, these deposits have formed large tufa dams, some several meters thick, that redirected the flow of the waterfall and created a series of terraces extending across the canyon floor.

Photo illustrating the impressive size of the Quaternary tufa deposit at Sitting Bull Falls, formed by calcium carbonate precipitation from mineral-rich spring water

 

Up-close view of the tufa deposit at Sitting Bull Falls, featuring flowstone layers formed by mineral deposition.

 These tufa deposits are Quaternary in age, representing a much younger phase of landscape evolution compared to the surrounding Permian bedrock. Together, the waterfall and its carbonate terraces illustrate how modern hydrologic and karst processes continue to shape and modify this ancient geologic landscape.

And that’s a wrap on Day Three!

From the intricate formations of Carlsbad Cavern and the Parks Ranch cave system to the active spring systems at Sitting Bull Falls, today’s stops reveal how ancient and modern geologic processes intertwine in the Guadalupe Mountains region. These sites not only showcase the beauty of mineral deposition but also highlight the ongoing influence of groundwater, climate, and biology in shaping the landscape.

Next up, we’ll head north to explore Bottomless Lakes, the Rio Grande Rift, and the dazzling dunes of White Sands National Park; a perfect finale to this geologic journey across New Mexico.