The Meandering Mud Pot

The Meandering Mud Spring of Salton Sea

Mikal Jakubal

November 16, 2023

In 2015 a nondescript mud spring near California’s Salton Sea did something unprecedented: it started moving across the desert at a before-your-very-eyes pace, snacking on a railroad line, regional highway, oil pipelines and fiber optic cables that foolishly failed to get out of the way.

At its peak in 2020 it was chewing its way across the desert at an unprecedented 20 feet per month. It has foiled the most heroic attempts by railroad and highway engineers to slow or stop it.

The main caldera at its present location is about 80 feet across with unstable, vertical sides several feet down to the water level where it looks like someone tossed a 50-pound Alka Seltzer tablet into it.

It is still moving now and I think it is one of the coolest things I’ve seen in a while.

The Niland geyser, also called the Mundo mud spring, an 80' wide, brown muddy spring with 3' vertical dirt sides. On the left is foam and turbulence generated by the upwelling of CO2 gas and water. Two rusty pipes cross the water's surface. Fiber optic cables hang above the pit, suspended from a line of poles on the other side.
The mud spring, looking SE on November 16, 2023. This place is fascinating. I just can't understand why all the cool Instagram van-lifers aren't here taking selfies.

Photos of the meandering mud spring of Niland will never appear in tourism promo brochures or “America’s beautiful landscapes” calendars. It’s an unsightly mess and not even a hot one: the sulfur smelling slurry is cool to the touch. I dipped my fingers in to test — because of course I did.

In the pit itself, two decommissioned oil pipelines seem to float near the surface, one obviously deformed and soon to be absorbed into the gurgling goop. Fiber optic lines sag overhead, temporarily suspended on poles, while black geotextile fabric drapes raggedly beneath the undermined and soon-to-collapse surface of the former bed of CA Highway 111.

Trucks roar by on the newly diverted highway a stone’s throw to the west and trains rumble on the re-routed tracks a few feet east. From the air, the bow-legged detours are almost comical. A giant pile of boulders waits to be swallowed whole, feeding the pit’s seemingly insatiable appetite. Sulfur dioxide and concentrated CO2 roil the surface of the brown slurry, presenting a potentially lethal atmosphere should you decide to take a little nap in the pit.

What’s not to love?

An aerial photo of the mud spring area showing wide, flat plains stretching into the distance. A highway and railroad line, enter from the top of the frame and then jog right and left, respectively, around the mud spring as they leave the frame. The mud spring itself appears as an somewhat circular hole several feet deep filled with muddy brown water. The photo is annotated to indicate the locations of: the spring, the roads and rail lines, the past and future route of the spring and the direction North.
Overview looking NW. The spring originally started hundreds of feet out of the picture. It will be interesting to watch its path.

Let me explain something here. I’m a total slut for quirky geology. This bubbling mud pit I’m trying to not fall into is no Old Faithful or Grand Prismatic Spring, but I’m enamored with it all the more for its don’t-give-a-fuck rawness. There are no tourists here, no railings, no National Park Service rangers telling me I can’t stick my fingers into the farting slime water. No one to scold me for rolling boulders into the pit for fun. I get to enjoy it all by myself this morning.

Imagine that.

Most of the famous geology-centered National Parks that people jam their RVs into every summer — Grand Canyon, Yellowstone or Arches, for example — are famous because they’re stunningly beautiful. Or, as John Muir described Yosemite, “sublime” (whatever that means). And they are! But, look, while I’m as enthralled as anyone by geology’s version of Italian Supermodels, l’m just one of a million other poor schmucks lining up to ogle them from the paved trails and guard-railed, crowded, Disneylandish packaged experiences that many National Parks feel like these days. My chances of getting an intimate minute alone with Delicate Arch in Arches National Park are about as good as a hot date with a catwalking supermodel. On the other hand, geology’s dive bars are good places to find some real one-on-one time with the weird kids. Assuming you like mud and rotten egg smell.

A small mud spring next to the larger one. Like the large one, this is a muddy hole filled with bubbling brown water. The muddy banks are slowly collapsing into it. In the background are the old and new highways, the latter with a vehicle passing by.
Small mud spring merging with the larger one. Note collapsing banks.

If you take a high school geology class or flip open any basic “Field Guide To Geology”, one of the first things you’ll learn is that there are three types of rocks: igneous, sedimentary and metamorphic. Like, whatever. I sometimes see things sideways, so I’ve made up a new term: “ignominious rocks”, the quiet, awkward nerds of tectonics that no one invites to the prom, so they spend the evening hacking everyone’s school email accounts or destroying railroad lines.

A common internet meme, using simple line drawings, shows a sad, lonely looking bald man with a party hat and a drink in one hand standing alone in the corner watch two couples dance, showing that he's been totally ignored and left out of the fun they're having. On his shirt are the words "Obscure, enigmatic geological feature" and above his head, as if he's thinking it "They don't know that I'm going to explode and bury half the continent in hot ash." The dancers are nominally male and female couples. One man's caption is "Stunning canyon as seen on Instagram" and the other's is "Iconic mountains named after a clothing brand." The women, representing people who only pay attention to geology when it's flashy and cool, are smiling and dancing with them. One has a caption "cool kids on Instagram" and the other has a caption "Fashion-conscious van lifers". Nobody's dancing with the lonely guy who is, it seems, more interesting that he looks.

Besides this rail-and-highway-devouring mud spring eating away the ground as I watch, I’ve had interesting encounters with other ignominious rocks: the tar that oozes from the sandstone and fouls the soles of beachgoers’ feet along the coast of Southern California; the sediment plug slowly migrating down the San Juan and Colorado rivers, obliterating everything in its path as the level of Lake Powell inexorably drops; the “blue goo” clay deposits that creep like clay glaciers in NW California, LOL-ing at Cal Trans’ efforts to keep Hwy 101 open; the magnetic anomalies in the Cascade Mountains that make compasses untrustworthy for navigation unless you are very skilled at adapting to your instrument’s Wheel-of-Fortune idea of which way north is. Reading up on any of these will take you down some of geology’s more fascinating rabbit holes.

I find learning about what makes these quirky rocks tick is often more interesting than, say, looking up why Half Dome exists. Not because Half Dome is not “sublime” (whatever that means), but because that information is readily accessible. Go to Yosemite and there is a visitor center dedicated to explaining it. Not so much with an unkempt, vagrant mud hole.

The mud spring showing the collapsing edge of the old highway. The muddy pit is to the left and about 80' across and about 3' down. On the right is the old highway. Soil has collapsed into the pit, exposing black geotextile underlayment that is now hanging into the water. It is clear that the roadway will soon begin falling into the pit.
Looking SE down the old Hwy 111 roadbed. The new detour is across the guardrail seen in the upper right. It's just a matter of time before the cement and asphalt starts falling in.

This peripatetic pit of peril is in what is known as the Salton Trough or Salton Sink, a geothermally and seismically active part of California between the Peninsular Ranges to the west and the Chocolate Mountains to the east, a little north of the U.S.-Mexico border and south of Interstate 10. The lowest part of the Trough is over 200 feet below sea level and still sinking. To picture what’s happening here, imagine the peninsula of Baja California doing the splits away from the rest of Mexico and California at a rate of about 2 inches per year until a time, millions of years from now, when it will crack off completely and become an island, moving northward along the San Andreas Fault with the rest of the Pacific Plate. As the land to the west moves away, the block of land in the Trough sinks into the resulting gap.

What’s causing this part of California to rip the seams of its yoga pants is the East Pacific Rise, a lava-spewing underwater crack in the earth’s crust that starts near Antarctica and continues all the way up into the Gulf of California. The northern extension of the crack is the Salton Trough, though it’s not yet underwater.

There are seafloor volcanoes in the Sea of Cortez between Baja and mainland Mexico and volcanoes have already erupted at the south end of Salton Sea as recently as 210 CE (1,814 years ago). The area is high on the USGS’s “most likely to erupt soon” list.

 The mud spring is not volcanic in origin. The carbon dioxide that drives it is off gassed as ancient Colorado River sediments are compressed into greenschist and sandstone deep in the earth. It’s one of many interesting products of the same tectonic movements that produce volcanoes, earthquakes and geothermal areas throughout the Salton Sink.

The Niland mud spring, also known as the Mundo mud spring and the Niland geyser just before sunset. The spring is an 80' wide hole of muddy water with a bubbling gas upwelling at the left side. Two old pipes cross at the water's surface and fiber optic cables are strung on poles overhead. In the background, a long freight train is about the leave the frame and extends into the distance. The three engines are yellow, followed by lines of mostly orange colored freight containers on flatbed cars.
Union Pacific train on the rerouted track. The original line went just left (east) of the mud spring's present location, about where the three cones are just left of center.

There are many other mud pots and mud “volcanoes” in the area, but this one is the “honey badger” of mud springs. From 2018 to 2020, extraordinary measures were undertaken to try to stop its progress toward the Union Pacific rail lines and Highway 111 but, when it came down to it, “honey badger don’t care.” It shrugged off every attempt to slow or detour it, including driving giant steel sheets deep into the ground in front of it. Railroad and highway engineers eventually conceded defeat and built bypass routes around the spring. When the pit eventually gobbles past the former paths of the rail line and highway, the detours will be abandoned and the lines rebuilt in their former locations.

Next on the mud pot’s menu after it crosses the highway is a National Wildlife Refuge parking lot, restroom and a dirt road, assuming it keeps a steady trajectory. If the spring’s path turns south a few degrees, there is an equipment yard with some buildings that might go bye bye. I hope that place has “meandering mud pit” insurance coverage.

A gloved hand holds what appears to be a long, drooping fishing pole over a bubbling, brown pool of water. Taped to the end of the pole is a small, square, plastic CO2 meter being held a couple feet above the water's surface.
CO2 meter taped to old tent poles to read the CO2 level in the pit. It occurred to me to get a fishing pole and sit there pretending to fish to see how long it would take for someone to see me from the highway and come over to be sure I was "okay."

For fun, I taped my home CO2 monitor to a tent pole and lowered it out over the main source of bubbling gas. It records up to 9,999 parts per million, but it maxed out and returned an error message, so I pulled it back to the edge, measuring the carbon dioxide concentration you’d be breathing sitting on flat ground at the caldera’s edge.

At over 8,000 parts per million, it is not life-threateningly high, but you’d probably feel dull if you hung out there too long. OSHA exposure limit is 5,000 ppm per 8-hour period, though the same chart suggests that under 15,000 ppm is not harmful for most people for short exposures. The thing to keep in mind is that CO2 is 1.5 times heavier than air, so will concentrate at the bottom of the pit. Yeah, I’ll pass on the mud bath.

A hand held CO2 meter made of milky white plastic about 3" x 3" showing an "Error" message on the screen. It is taped with strips of white tape to the end of a fiberglass tent pole. Below in the background is the brown bubbling surface of the pool.
This meter reads up to 9,999 ppm CO2, but maxed out when I lowered it to the pool's surface.
A close up shot of a hand-held CO2 meter, a small milky-white, square plastic box. It's screen shows 8424 in white letters on a black background, indicating 8,424 parts per million of carbon dioxide. In the blurred background is the surface of the mud pit where the CO2 originates.
CO2 reading at about sitting height above the edge of the mud spring, on the downwind side.

The mobile mud spring is easy to find and visit. According to the Wikipedia article, the site is closed off, but there are no signs, fences or other restrictions on site as of this writing. About five miles north of Niland on Hwy 111 you’ll see the recent road construction and the warnings that the 55mph zone will be enforced. Turn off to the east on Gillespie Road and park wherever. It’s right there.

For now.

Notes and some cool links.

The Wikipedia page calls it the Niland Geyser and gives a good overview, though from everything I read, it’s not technically a geyser because it’s not hot and doesn’t eject water out of the pool.

Here is a good overview of the Salton Sea itself.

This has some great animations of how the Colorado River sediments have kept the Sea of Cortez from flooding the Salton Trough.

This symposium has a detailed explanation of the geology and the efforts to stop the mudpot. The mud pot presentation can be found by scrolling about half way down the very long pdf. Look for Mundo Mud Spring presentation.

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