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SAN DIEGO — Southern California is home to countless natural wonders spanning the region’s diverse landscape. Among those destinations, hidden deep in the badlands of Anza-Borrego State Park, is a cave system that scientists believe is the largest of its kind in North America.

Called the Arroyo Tapiado Carrizo Mud Caves, the cave system is estimated to be a distance of several miles long through the park’s southern badlands, with individual caverns measuring as large as 130 meters deep and 1,000 feet in length.

The mud caves are just one of numerous distinctive geological formations in the Anza-Borrego southern badlands that includes popular destinations like Font’s Point and the Wind Caves.

But unlike some other formations in the area that are one-of-a-kind oddities, what makes the Arroyo Tapiado pseudokarst formation unique is not necessarily how the caves were made – it’s how it ended up.

“Mud caves can be found all around the state,” Dan McCamish, a senior environmental scientist with the California State Parks Colorado Desert District, told “The geological processes … (are) very similar to what you see here, but you’re seeing it on a geologically grander scale.”

“Most cave systems don’t have 1,000 foot long passages – they shorten before that,” he continued, “or they’re not 100 feet tall or 50 feet tall at some of their ceilings.”

This scale is something that McCamish says could have only happened given the combination of distinctive conditions in the southern section of Anza-Borrego State Park.

As McCamish explained, the part in the badlands where the Arroyo Tapiado Carrizo Mud Caves can be found – known as the Fish Creek area – used to exist under a shallow marine environment, where dissolved solids drained down to the bottom of a lake bed.

Roughly 2.8 million years ago, that bed dried over time and uplifted given the area’s hyperactive tectonic movement along the San Ysidro and Elsinore faults – exposing the formations to additional erosion that wore away at sand and clay forming drainage caves through the malleable soil.

Periods of heavy rainfall cut channels through the formation, which McCamish described as a “loose conglomerate” of very dry, rock soil made of sand, silt, mudstone and other sediment.

That erosion in the badlands environment created one of the most extensive and exposed known cave systems on the continent, with each cavern sculpted in its own unique shape, size and make-up of layers. McCamish says it also gave the system its Spanish name, Arroyo Tapiado, which roughly translates to “walled wash.”

“These mud caves offer a unique perspective, in that you can see this massive, long-term formation in a wilderness area,” McCamish said. “It is near the Badlands where the geologic uplift occurs and it isn’t covered by vegetation – you can see this soil, you can see these caves.”

“We can look at our geology in a different way than we would either in a suburban landscape or even a temperate area where the hills and rocks and geology are all covered by vegetation,” he continued.

For those that want to visit the Arroyo Tapiado Carrizo Mud Caves, the location of the system is accessible by vehicle, however, the route goes right through a dry wash area that floods easily when it rains, with no paved road. 

Because of that, McCamish said it’s important to check the weather before heading out to ensure that conditions allow access. Four-wheel or all-wheel drive vehicles are also needed to get through the dips and loose rock sections of the route.

Once you get to the system, it is free to explore and walk through certain sections of the cave formation using extreme caution, as McCamish says the caverns are dangerous and can collapse. Given its fragility, do not climb the mud caves or attempt to walk on top.

“If you are to enter (the caves), I would say you are assuming a moderate to high risk,” McCamish said. “All of those unique things that make them interesting to see … also make this area exceptionally treacherous.”

Those that want to adventure inside are urged to do so responsibly – travel with someone else, avoid picking pieces off the formation and bring supplies like a light and a helmet to help with the dark, often small spaces that lead to the larger caverns.

Here are some other tips McCamish shared for adventurers who might want to head out to the Mud Caves:

  • Plan ahead and prepare accordingly before leaving your house. Know where you’re going and how you’re getting there. Tell someone where you’re going and when you expect to be back.
  • Be ready for hot temperatures and try to avoid visiting the cave system during the sun’s peak – either early in the morning or later in the afternoon. Summer is fast approaching, meaning temperatures could hit the 100s when the sun is at its apex.
  • Don’t count on cell service – it can get quite spotty throughout the park, especially in the area near the Mud Caves. Whether you use it for navigation or communication, bring along some analog back-ups, like a physical map or a non-cell-reliant, GPS-capable device.
  • Bring food and water. McCamish recommends at least a gallon of water per person for a full day trip in the park.