Self Discovery in Selenite Moon Cave

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The Pecos Valley is one of the densest caving regions on Earth, with more than 10,000 caves — many unmapped, and many more not surveyed in decades. When I first moved to Carlsbad, New Mexico, I knew that I was going to make caving a big part of my life. However, I wasn’t really aware of just how big of a deal it would become for me, or how high my priority list it would end up. Naturally as a beginner, I started looking for ways to expand my skills, milestones to look forward to, and goals to work towards. After joining the local grotto and meeting some incredible like-minded folks, I realized the first thing I needed to do was learn the ropes (literally). I needed to learn to ascend and rappel.

The author in rappelling gear just inside the entrance of Selenite Moon Cave.

I generally pride myself on self-sufficiency, but I also pride myself on remaining alive, so in caving, I really needed to meet a mentor for these kinds of skills. I met a friend through the grotto who was very keen on mentoring new cavers in rope skills, and he took me under his wing. He had an awesome setup in his back yard, with a rope threaded through a loop at the top of a metal frame, secured to the ground with a bar rack. This allowed the rope to be used as a treadmill, so a trainee could climb indefinitely. While this type of setup obviously requires some vertical space — about 15 feet at least – it’s an ingenious idea, and has great utility for a caver-in-training. After a few practice sessions with two types of descent-control devices – a bar rack and a bobbin — I passed the NCRC vertical exam and was ready to go into my first vertical cave.

Something I appreciate about geology, particularly as it pertains to caving, is that it allows you to truly get a four-dimensional experience of the environment — the three physical dimensions, and the fourth dimension being time itself. You can tie virtually any subject of study or conversation back to the geology of the regions of pertinence. Here in the Pecos Valley, that means dropping into one of the most geopolitically important and strategic regions anywhere in the world. The Permian Basin — in which the Pecos Valley is nestled — is the largest oil-producing region in the United States; it was responsible for an astounding 48% of total U.S. crude oil production in 2024. If it were its own country, it would rank fourth among the top oil-producing nations in the world — behind only Saudi Arabia, Russia, and the rest of the United States, and beating out Canada and Iraq. If it were anywhere else on Earth, the U.S. would have lots of “strategic interests in the region.” However, since it’s already inside of the United States, the cavalry doesn’t have to roll in — something that has also certainly never happened before.

In an area with such a high density of caves, also evident is the incredible diversity of them. Most people, when they think of caves, picture limestone caves like Carlsbad Cavern, the most famous cave in the region. Limestone caves, however, are only a small sliver of the actual breadth of different types of karst features that can form. In fact, solution caves don’t even have to form in carbonates (limestone, dolomite, or marble); many form in evaporites such as gypsum, anhydrite, or halite. Gypsum caves are fairly common in the Pecos Valley; the longest gypsum cave on public land in the U.S. is Parks Ranch Cave, the very first cave that I went in — not counting developed show caves.

The reason for the prevalence of these evaporite caves is the same as the reason for the region’s oil production. During the Permian Period (~251-299 million years ago) this region was underwater; covered by a series of inland seas. The Delaware Sea, which covered the region around Carlsbad, NM, was one of those sub-basins. As tends to happen in restricted inland seas — warm, shallow, and cut off from circulation with, say, the ocean — it accumulated organic material in the muds on the bottom of the seabed, and as the sea level lowered, the concentration of both that organic material and also of salt in the water rose. The result over millions of years is the Permian Basin today, made up of layers of organic-rich sediments and evaporites/limestones. Pressure and heat created hydrocarbons which ended up locked under impermeable caprocks — such as those layers of evaporites and limestones — and eventually the oil industry came along and started drilling to get them out. Further up, near the surface, the lowering of the water table, sulfur-oxidizing bacteria, and rainwater began to carve out the passageways of the various caves that exist in the region today.

For my own first vertical cave experience, we had plenty to choose from. We decided on a nearby gypsum cave called Selenite Moon Cave. It’s fairly obscure; there’s very little information on it anywhere. In general, gypsum caves make me nervous. Because they form in runoff channels, any and all rainwater from a storm will rush into them and flood the cave. To put it another way: if it suddenly rains while you’re in the cave, you’re dead. That doesn’t instill a lot of confidence in me, particularly in a part of the country where sudden rains are not all too uncommon. This made it imperative to check cloud cover before we went in — and fortunately for us, there wasn’t any that day, so we were all good to go.

The opening of Selenite Moon Cave

To get to the cave, the first thing you need to do is make your way down a BLM road between Carlsbad and Hobbes for a considerable distance. Since cavers are only slightly less protective of their spots than hunters and fishermen, I won’t say too much more than that, apart from the fact that you then park next to an oil pad and walk a few hundred yards out into the desert before you come up on a big runoff ditch, and eventually, as you follow a trail of selenite crystal mosaics, you find the entrance to the cave, which is a pretty unassuming-looking crevice in the rock, a little taller than I am but very narrow, and the first rappel is only a few feet into the cave. Rattlesnakes frequently crawl into the entrance of the cave and sometimes even down past the rappel, which can make getting off the rope a bit spicy. There was even a long-dead one that had been claimed by mold at the bottom. We tied off, and the two people I was with went first before it was my turn. All my training paid off when the 35-foot rappel was a breeze. After that initial one, another short rappel gets you to a spot where you can finally take off the vertical gear and explore some of Selenite Moon’s passageways a little more comfortably.

A mold-covered dead rattlesnake inside the cave at the bottom of the rappel.

Rattlesnakes aren’t the only critters that find their way into Selenite Moon; the frogs are ubiquitous. More accurately, the toads are ubiquitous, and you’ll see various species throughout your time in the cave, such as this Texas Toad. These little guys get into the cave through various means – being washed in by rainwater among those. I’m not sure how long they live after that happens – there are insects including cave crickets inside the passageways which would certainly be enough to sustain the toads, but in such a dark environment, I don’t know if they are able to find the prey or not - none of them looked particularly malnourished though. I am sure some escape, but I suspect that most stay within the confines of the cave. Perhaps one day I’ll get a herpetological collections permit from the state and return – maybe even just to take home a Texas Toad as a pet.

A Texas Toad (Anaxyrus speciosus) inside of the cave

The cave itself is strikingly beautiful. There are places within it where the reason behind the name Selenite Moon becomes apparent. To explain: Selenite is a form of gypsum (CaSO4 · 2H₂O) that forms when gypsum crystallizes in large, well-structured crystals, which happens when growth is uninterrupted by environmental conditions. When environmental conditions are more chaotic, like in cases where there is fast evaporation, a high sediment load, or repeated dissolution and reprecipitation cycles, regular gypsum crystals will form; they’re typically of a very sugary texture. Something really amazing about Selenite Moon Cave is that you’ll quite often see both in the same spot. So, within the cave, you see evidence of both types of environmental conditions at different times in the past. Even more amazing than this, and reflective of the beautiful mixed geology of the Pecos Valley, is the presence of flowstone. As carbonate-rich water trickles through from limestones above the cave, small limestone speleothems form – such as this stalactite, which has grown right next to a patch of selenite crystals.

Stalactites right next to selenite.

This is the fourth-dimensional experience of a cave; a plunge into the depths of time itself. Periods of environmental chaos, calm, and change are present before your very eyes. To wriggle through a cave is to dance with geology. It is to be reminded of not only the power, but the longevity, of the forces of Earth itself; forces we engage with every day, but are somehow oblivious to through hundreds of layers of dissonance. But in a cave, these connections become apparent, and impossible to ignore. Beyond even the physical splendor of the underground world is the physical dance itself. The amount of contorting, wriggling, crawling, and climbing one has to do, even a cave that is not particularly difficult to navigate like Selenite Moon, dwarves the physical challenge of anything else I have ever done – save for maybe hunting. And in this cave, I got my very first taste of just how physically demanding things can get underground.

The three of us had gone down a narrow passage about as far as we could before a steep drop. Two of us belayed down into it to see where it led beyond the drop; one, the trip lead, stayed up top to help us get out. When we came to the end of the passageway and confirmed it was a dead end, we turned back to take on the task of getting out of the passage. There were no handholds to climb up out, so it was on us to get each other out. First it was my colleague’s turn, so from above, the trip leader pulled the ropes and I put my hands under her boots to lift. She scrambled out easily with our help. But then came my turn – weighing in at around 200lbs, and with no one to lift me from below. With no handholds, we effectively conducted what amounts to a small-party assisted rescue. The two of them threw together a quick haul system up top to pull me upward, I did what I could with my own hands and feet against the walls of the passageway, and in tandem, we worked slowly but surely to pull me toward the top. It was exhausting, and all the while, my mind kept wandering; the mental weight of “if it rains, you’re dead” began to gnaw at me. I knew I’d get out, but how soon? I will admit, it started to heighten my sense of urgency a little more than it probably should have. I felt panic start to creep in – more than the situation warranted, but still real nonetheless.

Once I got near the top, I found a place I could grab into, just below the ledge, which allowed me to rest and ground myself. I knew the risk of a sudden rainstorm was low. I trusted my trip lead’s skill to get me out if things went wrong. My mind still wandered, but in more passive, observational ways this time. Being bound by the structures around me got me thinking about how fragile human beings are. I was no more powerful to change the confines of my situation than a glass bottle lost at sea is to change the currents and the tides. I was simply working within the system, and was left with no choice but to relax into the situation as it was.

The time came for one last push. There was a ledge above me that I knew I could use to push myself out. The problem was that I wasn’t going to be able to reach it with my hands, so I did the next best thing. I grabbed the trip leader’s boot with both hands and kicked my legs backward and upward like a scorpion’s tail until my feet touched the wall – flexibility is a big plus in a cave. Then, with all my might, I pushed against the wall and pulled on his boot until I was within arms reach and able to get out. We celebrated briefly, then headed on.

My mind was still glued to where it had gone earlier when we happened upon a flake of chert that had been broken off during the creation of a stone tool by someone many centuries prior. At some point, it had washed into the cave by the same forces that created it, and continued to create it. Chert isn’t native to the Pecos Valley – someone had to have traded for it, or travelled to gather it. It illustrated further how the forces of our environment are out of our control. Salt here, chert there; resources scattered across the land by forces hundreds of millions of years older than the people who needed them. Just as I had been trapped by stone walls and reliant on others to escape, so too had they been bound by the bedrock beneath their feet.

As I emerged from the cave and felt the cool nighttime breeze of the desert blowing the sweat off of my face, I saw the lights of thousands of oil rigs lighting up the Permian Basin as though it were a city. My mind turned to the bigger picture. What I said earlier in this piece about how you can tie any topic of study or conversation back to geology – it’s true. Here, the same processes that turned this place into “The Yosemite Valley of Caving” also turned it into a landscape totally characterized by big oil. I thought about how travel and trade in modern times largely revolves around places like this; how highways and shipping routes had to be constructed to get to this place to allow for that transit of goods around the globe. I thought about what oil drilling had done to the natural beauty of this place; from the lights of the rigs drowning out the night sky to the air pollution to the physical destruction of caves by oil drills. And all of this determined by forces billions of years old.

Broadening the scope, I thought back to that chert flake, and about who made it. Perhaps Mescalero Apache; perhaps Southern Ancestral Pueblo. I considered the beautiful and rich cultural traditions associated with those indigenous groups, and the diversity of indigenous cultures worldwide. I thought about the Ancestral Polynesians and their long voyages throughout the Pacific, using the stars above and the currents below to guide them. Those currents weren’t invented by people; rather, people inherited them. influenced by seafloor topography, continental positions, and ocean gateways which change over time in slow but real ways.

Travel routes today are no different – the ocean currents and the winds above, which powered the ships of yore and the highways of now, are all shaped by geologic influence. A country's chief imports and exports will be tied to what is, or is not, present in its location; which is determined by geology – either directly, like the presence of iron, coal, oil, cobalt, lithium, etc., or indirectly, by creating the soils that allow for farming, or for dense, healthy forests to be logged, or for the richness of game that allowed one particular civilization to become healthy and sustained enough to advance forward. Through hundreds of thousands of years of those compounding forces shaping our world, who can say with certainty that any of us have free will, if our destiny comes down to a genetic lottery and a world shaped by billions of years – hundreds of billions of human lifetimes? We are the ocean currents; not acting on our own free will, but being influenced by forces beyond our control and greater than us. Each person is a beautiful creation of happenstance, carrying with them a knowledge and experience that is, and can only have been, shaped by those influences. Each culture is, in turn, a creation of collective happenstance. When those people band together, they can create beautiful things; art, poetry, a mediocre outdoors blog, or music. This is the foundation of culture, and choosing to experience cultures other than one's own may be the only true form of free will that humans have.

To descend into a cave is to surrender oneself to the mercy of those same all-powerful forces. To enter the wild in any capacity is to do such. Perhaps that is the reason why so many people feel uncomfortable in the presence of truly wild places. It requires us to confront our deepest feelings of insecurity in the presence of nature, in the most intimate and direct way possible. For me, it’s what keeps bringing me back. Even the impulses of my own mind that draw me to the wild were shaped by my homeland, the Ridge-and-Valley Appalachians, having the combination of fertile enough soil to support the farm I grew up on, and enough natural beauty to keep me interested in venturing off into the woods and along the creeks. Perhaps this is the true beauty of Earth – not our free will, but our lack of it.