This piece is part of a special project on deep time examining what the Western U.S. was like thousands, millions and even billions of years ago, and how that history is still visible and consequential today. Read more stories from the series.

For many of us humans, old trees — gnarled oaks or towering redwoods — are sources of psychological comfort. As elders who have weathered earlier times of crisis, they signify continuity and resilience. Their rings bridge present and past and remind us that our “now” is only one of many.

But for longer-distance time travel, we must seek out even more ancient ancestors. The ones with the longest memories, full of insights germane to our Anthropocene anxieties, are right here in our midst: the rocks beneath our feet. Although rocks have an understandable reputation for taciturnity, they are, in fact, speaking to us all the time, sharing their recollections about Earth’s past, ready to reward patient listeners with perspective-altering memories. They represent Natural Intelligence — a mature counterpoint to the artificial kind.

Wyoming is an especially good place to listen to stories from deep time, because the rocks exposed at the surface include the oldest in the Western U.S. and span almost 80% of Earth’s history, from 3.5 billion years ago to the present — among the longest and most continuous records of any place on the planet.

Those who spend enough time in the company of rocks may begin to feel that they are in dialogue with them. I am one of those: For 40 years, I’ve studied the language of rocks and found them to be wise mentors and matchless storytellers. Seeking existential reassurance at a disheartening time, I recently asked 10 Wyoming rock formations to share accounts of the Wyomings they knew when they were young.

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Wyoming’s oldest rock, the Sacawee Gneiss, was crystallized from magmas derived from melting of still older granitic rocks, none of which survive today.

Sacawee Gneiss

fiery foundations

Age: ca. 3.45 billion years (Paleoarchean Era)

Exposure: Granite Mountains

Sacawee: ​​Hi. I’ll go first because I was here first. I’m the original Wyoming. I’ve seen the planet itself change. Earth was utterly different in my youth: much hotter than today, roiling and restless, hadn’t even fully adopted the practice of plate tectonics yet. The Earth I was born into had magmatic activity everywhere, no proper continents, just a few dozen islands of granite.

The only mementos I inherited from my ancestors are some crystals of zircon that survived from their own youth. I’ve offered some of those up for analysis.

Marcia Bjornerud: Yes, thanks for those. Zircon crystals are like tiny time capsules. We’ve figured out how to calculate their ages as the uranium in them slowly decays to lead. Some of the zircons you gave us record the time when you crystallized; that’s how we know how old you are.

Sacawee: There were a bunch of us born around that same time. I have siblings in southern Minnesota and northern Michigan.

MB: I’ve met them: the Morton and Watersmeet Gneisses.

Sacawee: Yes, OK, I forget that you assign names to everyone. After we crystallized, we all went through the same arduous rite of passage below the Earth’s surface — kneaded and folded almost to the point of dismemberment. Not something you mortals would survive.

As we warmed up and relaxed, we flowed and took on new forms — in truth, it was thrilling. Deformation and metamorphism left us with these spectacular stripes, which I wear proudly. What we didn’t realize then was that we were becoming the foundation for one of the first real continents.

MB: We call it the Superior Craton.

Sacawee: Now that’s a good name.

MB: I’m afraid it’s not a description — it’s a reference to the biggest lake in North America.

Sacawee: The biggest lake in your time.

MB: OK, the biggest for now! But it is a great lake.

Sacawee: Anyway, we Superior siblings stuck together until about 2 billion years ago. Then, under the new plate tectonic regime, I got separated from the others when the crust split along a great rift zone and an ocean opened between us. Our paths diverged for a while, but a couple hundred million years later, plate motions shifted, and they started heading back my way. We ended up running right into each other, with a great mountain range rising along the seam where we collided.

MB: We call that mountain range the “Trans-Hudson” belt. We need these names to keep track of so many earlier geographies, and need to consult so many rocks to get the whole picture. Other landmasses were annexed to the Superior Craton around the same time, and that’s when modern North America really began to take shape.

Eventually, like all mountains, the Trans-Hudsons were leveled by erosion. Their roots peek out in today’s Medicine Bow Mountains in southernmost Wyoming, but most of the great Trans-Hudson range now lies deep beneath the Dakotas and Saskatchewan, buried under younger rocks.

Sacawee: Well, it’s safer down there. Up here at the surface, I’ve had a taste of what it must be like to be mortal; I’ve been sandblasted by wind, gouged by glaciers, dissolved by rain. I’m being reincarnated, slowly, as sediment, which may one day become sedimentary rocks.

MB: We mortals can only envy the infinite cycles of rebirth and transformation you rocks take for granted.

Sedimentary rocks are the methodical archivists of the rock kingdom, recording the ever-changing conditions at Earth’s surface. The Nash Fork Dolomite was deposited as calcium carbonate mud in the shallow ocean waters that split the old Superior Craton.

Nash Fork Dolomite

empire of microbes

Age: ca. 2.1 billion years (Paleoproterozoic Era)

Exposure: Medicine Bow Mountains

Nash Fork: My Wyoming was a water world. It was an energetic place, an exciting time. Tides were much higher because the Moon was closer. And the day was shorter — just over 19 hours — because the Earth was spinning faster. There were no land plants, but the waters teemed with photosynthesizing cyanobacteria, which had by then begun to change the atmosphere.

MB: That’s what we call the “Great Oxidation Event” — a huge inflection point in Earth’s history. Before that, the planet’s atmosphere was essentially just “volcano breath” — mostly carbon dioxide and water vapor.

Nash Fork: In my time, microorganisms were still learning to use oxygen, evolving novel strategies for living. They formed great shallow-water collectives — vast, lumpy mats of diverse microbial species coexisting symbiotically, with the metabolic wastes of some serving as the nutrients for others.

You humans call them stromatolites. I’ve heard you describe their shape as “cabbage-like,” which is a bit rude — stromatolites are remarkable, complex, robust systems. You could pick up a few lessons from them, such as how diversity and deep recycling are essential to durable communities.

MB: Your stromatolites are spectacular. Geologists have declared your outcrops a “no-hammer zone.”

Nash Fork: Thank you for that, but I’ve noticed that most humans have a terribly biased, “size-ist” view of the biosphere — you don’t seem to think anything of interest was happening until the first animals appeared about 550 million years ago. Well, single-celled organisms dominated the biosphere for long before that. After they ushered in the era of oxygen, they buffered the chemistry of the atmosphere and oceans, keeping the Earth on an even keel for the next 2 billion years.

It was only after animals emerged, with their gigantic appetites and elaborate food webs, that the carbon cycle became prone to destabilization and the biosphere vulnerable to mass extinctions. I’m sure some of the others will tell you those horror stories.

The ancient ocean documented by the Nash Fork dolomite disappeared in the tectonic collision that built the Trans-Hudson mountains. After that, erosion outpaced deposition, and rivers incised deeply into the bedrock, leaving an irregular surface called the Great Unconformity. In Wyoming, the Great Unconformity represents a gap in the geologic record of more than a billion years.

Great Unconformity

ghost worlds

Age: ca. 1.7 billion-500 million years (Mesoproterozoic Era-Early Cambrian Period)

Exposure: Big Horn and Wind River ranges; Shoshone Canyon east of Yellowstone

Great Unconformity: Frankly, I’m surprised you’re even interviewing me. Geologists generally treat me as a nonentity. I’m an un-rock, a cipher, just an irregular surface. But I’m actually pretty famous: People marvel at me in the Grand Canyon. It took a lot of patience to dismantle all that rock, erase mountains and become what I am. I feel like that merits respect.

MB: I think geologists do respect you, but you represent absence — negative space — and we’re not good at reading that.

Great Unconformity: I admit that I have some big gaps in my memory. What I do know is that sea level must have been pretty low in my time, because if it had been high, I would have been covered with water, and sediment would have collected instead of eroded.

Toward the end of the period the Great Unconformity represents in Wyoming, the planet experienced a long and extreme cold spell called “Snowball Earth.” Massive glaciers covered the continents, even in the tropics. With so much of the world’s water locked up in ice caps, sea level was exceptionally low. When at last the Earth warmed up again, the ocean rose dramatically, flooding the denuded continents. The Flathead Sandstone records the steady rise of the seas across Wyoming’s deeply eroded landscape.

Flathead Sandstone

an advancing beach

Age: ca. 520 million years (middle Cambrian Period)

Exposure: Big Horn and Wind River ranges; Teton Pass

Flathead: I’m part of a great sheet of beach sand, now hardened into stone, that blanketed the continent in the aftermath of that fearsome ice age. I have counterparts across North America, all draped over the Great Unconformity: the Tapeats Sandstone in the Grand Canyon, the Sauk Sequence in Wisconsin, the Potsdam Formation in upstate New York.

The Wyoming I encountered was a bit austere — still no land plants — but what a wonderful variety of rocks exposed at the surface: contemporaries of Sacawee and Nash, and many others. A real range of types and temperaments! I’m still in contact with all of them today, and I mean that very literally. Anywhere the Unconformity and I are exposed together, you humans can see where I met these different rock formations and get a glimpse of the land surface as it was in those days.

MB: Yes, it’s always a thrill to find you stretched out atop the Great Unconformity. Each outcrop is a portal into Cambrian time.

We geologists have long admired the creamy beauty you and other Cambrian sandstones share — you’re almost entirely quartz, which must have been eroded out of granites and gneisses like Sacawee. Your sheer volume attests to the enormous amount of igneous and metamorphic rock that had to be weathered to yield so much quartz.

Flathead: Another tip of the hat to the Great Unconformity. A lot can be accomplished in a billion years.

MB: Until quite recently, though, we tended to dismiss you quartz sandstones as, um, rather inarticulate. Quartz doesn’t have a good memory of its origins, and it seemed there was no way to track where, exactly, all your sand came from.

Flathead: I know; it took you a while to notice that a fraction of our sand grains are made of zircon.

MB: We call these “detrital zircons” — sedimentary particles that came from igneous and metamorphic rocks, typically carried by rivers over long distances before being deposited. They’re rare needles in vast “haystacks” of quartz. Learning to interpret them has been like discovering whole libraries we didn’t know existed. They’ve made it possible for us to reconstruct long-vanished drainage systems at the continental scale.

And to think that until recently we thought quartz sandstones had nothing to say!

Flathead: It’s fine. You’re young, and we’re patient.

Later in the Cambrian Period, sea level rose even further, and the Flathead beach sands were buried by deeper-water carbonate rocks. Eventually, Earth’s climate cooled, and the seas retreated again, exposing the landscape. The Tensleep Sandstone records this re-emergence.

Tensleep Sandstone

desert dunes

Age: ca. 310 million years (late Carboniferous Period)

Exposure: Bighorn Mountains; Tensleep Canyon

Tensleep: I’d like to point out that not all sandstones were laid down by water. I’m a sandstone, too, and my Wyoming was a barren dune field. Land plants existed in my time, but not in the desert where I was born. All I remember is the merciless wind — cruel and unrelenting. Look closely at my quartz grains — they’re pitted and scarred to the point of opacity. Eventually, another sea rose and shielded me from that torment. What a relief! Then I had a few hundred million years of blissful sleep — until you humans discovered that I contain oil and started perforating me with drill holes.

MB: That water you speak of — the Phosphoria Sea on the western edge of the continent — was both your salvation and your nemesis. Without it, you probably would not have been buried and preserved in the rock record, but its exceptional biological productivity later made you a target for Anthropocene capitalists — because over time, that rich organic matter decomposed into petroleum that seeped down into your permeable dunes, now tapped by countless oil and gas wells.

Wyoming was still on the edge of the continent during this time: The sea that rose and shielded Tensleep formed a deep basin in parts of present-day Idaho, Utah, Nevada, Montana and western Wyoming. Upwelling coastal currents carried nutrients into the shallow waters and fostered an unusually rich marine ecosystem. The Phosphoria Formation records this time of exceptional biological productivity.

Phosphoria Formation

biological bacchanal

Age: ca. 290 million years (early Permian Period)

Exposure: Outcrops along Hwy 191 north of Jackson and Hwy 28 south of Lander

Phosphoria: Let me tell you about that bountiful sea; its warm, sunlit waters deposited organic-rich mud that hardened into my shales and limestones. My Wyoming was a tropical marine paradise. Waters absolutely teeming with organisms: brachiopods, sea snails and sponges covering the seafloor like a living carpet; phytoplankton thriving at the surface, feeding exuberantly on nutrients from deeper waters.

MB: In a state of “phosphatic euphoria” — that’s what I think of when I hear your name.

Phosphoria: About right. Oh, and the fish! So many sizes and varieties, schooling and darting. I managed to collect and preserve many of their scales. And there were some real weirdos — like those big bizarre ones with crazy tooth whorls on their lower jaw.

MB: Oh, my gosh, yes — we’ve named them Helicoprion. The name means “spiral saw.” That fearsome coil of teeth might have been good for ripping through soft-bodied prey.

Phosphoria: Of course, what we didn’t know then was that our beautiful ecosystem and most of its members were doomed. The entire world was about to crash.

MB: Yeah, the end-Permian extinction; I didn’t want to bring it up. Great eruptions of lava in what is now Siberia spewed an enormous amount of carbon dioxide into the atmosphere, setting in motion a perfect storm of environmental calamities — abrupt global warming, ozone destruction, ocean acidification and anoxia, eventual ecosystem collapse — the most severe mass extinction in Earth’s history.

Phosphoria: I’m glad I remember the world before all of that happened.

MB: Well, we in the Anthropocene have studied that world and its biodiversity with great interest, but mainly, I must admit, to plunder it. Your phosphate-rich shale deposits, some of the largest in the world, have been strip-mined for fertilizer, and the remains of your exuberant phytoplankton fuel our oil-driven economy. In a terrible irony, our dependence on ancient ecosystems like yours is leading us toward a reenactment of the Permian catastrophe.

The Permian extinction was a near-death experience for the biosphere. At least 80% of known marine species, including many in the Phosphoria Formation, went extinct. In Wyoming, the Chugwater Group, easily recognized by its intense red color, records what happened next.

Chugwater Group

post-apocalyptic landscape

Age: ca. 240 million years (Triassic Period)

Exposure: Wind River, Bighorn and Powder River basins; Red Canyon Overlook

Chugwater: The world didn’t end after the Permian extinction. My Wyoming was hot and dry, and vegetation was sparse. Rivers coursed across the arid landscape in braided patterns, dropping sand and silt along the way. Sometimes water pooled in brackish basins, and their brines permeated my river sediments, forming white lenses of gypsum.

MB: Although I know you represent that inhospitable environment, your brilliant red-orange hue always seems so warm and welcoming. Your color makes you easily seen from space! Wherever you crop out, you brighten the landscape.

Chugwater: That’s sweet of you, thanks. I owe my vermillion to trace amounts of oxidized iron — or, let’s just call it what it is: rust. Doesn’t take much rust to stain everything!

MB: True, and it doesn’t take much oxygen to make rust. We think that oxygen levels remained low for millions of years in the aftermath of the Permian apocalypse; marine photosynthesizers struggled to re-aerate the oceans. And some paleontologists even think that the reason dinosaurs gained an edge over other reptile groups was that their respiratory systems — which they passed on to modern birds — allowed them to breathe more efficiently.

Chugwater: In fact, I’ve got some of the oldest known dinosaur fossils in North America. My environmental circumstances made it difficult for me to hold on to entire skeletons, but I’ve preserved a few bones.

MB: Don’t be so modest: Your fossils of a silesaurid femur and humerus have recently overturned the long-standing idea that dinosaurs were limited to the Southern Hemisphere until Jurassic time.

The Morrison Formation is famous around the world for its dinosaur fossils.

Morrison Formation

jurassic park

Age: ca. 150 million years (Jurassic Period)

Exposure: Como Bluff near Medicine Bow; Hwy 120 north of Thermopolis or north of Cody

Morrison: Yes, I’ve got the dinosaurs. Herbivores like stegosaurs, camarasaurs, apatosaurs and diplodocus, but some meat-eaters too, mainly allosaurs. Drives me crazy, by the way, that most of the dinos in the Jurassic Park movies are actually Cretaceous species, 80 million years younger than me.

My Wyoming was warm and semi-arid — I’ve been told it was a “Mediterranean climate,” though of course the Mediterranean Sea didn’t exist then. Flowering plants weren’t around yet, but gymnosperms like ginkgo and cycads grew everywhere and managed to feed all those huge plant-eaters. Like Chugwater, I’m made of the fine-grained deposits of rivers and lakes that attracted thirsty creatures.

MB: The dinosaurs’ melodramatic demise gets as much press as the creatures themselves. We humans seem to project our own fears onto the cataclysms of the past. The asteroid impact theory gained traction in the late Cold War years when the specter of nuclear holocaust loomed large in the public psyche. Today, almost all geologists agree that a large rock from space did strike Earth at the end of the Cretaceous, but there is an emerging view that other factors — including a spike in greenhouse gases from volcanoes in India — also wreaked havoc on late Cretaceous ecosystems.

The periods just before and just after the dinosaur extinction 66 million years ago are well represented in Wyoming’s rocks and landscapes. Around that time, over an interval of about 30 million years, an unusual tectonic episode called the Laramide Orogeny thrust up the mountains people think of as “The Rockies”: the Bighorn, Wind River, Beartooth, Uinta, Granite, Laramie and Front ranges.

In most mountain-building events, the tectonic action is close to the site where two tectonic plates converge. The strange thing about the Laramide ranges is that they rose 800 miles inland from the plate boundary off the coast of Oregon and California. This probably had to do with the difficult subduction of an oceanic plate called the Farallon, which was apparently too buoyant to sink into the mantle, the vast region that lies beneath Earth’s crust. The Farallon seems to have scraped along the base of the North American plate without encountering too much resistance until it hit the deep crustal roots beneath Wyoming — the ancient craton forged by the Sacawee Gneiss.

While this tectonic upheaval was happening, seas rose and fell, a massive space rock struck Earth, the dinosaurs perished and, eventually, the world experienced a period of dramatic upsurge in the concentration of carbon dioxide in the atmosphere and abrupt warming known as the Paleocene-Eocene Thermal Maximum. The Green River Formation — considered by many Earth scientists to be a “distant mirror” for our own time — recorded the aftermath of this event.

Green River Formation

hothouse world

Age: ca. 50 million years (Eocene Epoch)

Exposure: Fossil Butte National Monument

Green River: My exquisite fossils of leaves, insects, fish and amphibians are sold in rock shops around the world. They preserve exceptional anatomical details, sometimes even of soft tissues. And, hey, Nash Fork, I also have freshwater stromatolites! I accumulated as muddy sediment and organic matter at the bottom of a chain of ancient lakes, and I preserve detailed records of the plants and animals living in the water and along the shores.

My Wyoming was subtropical — hot and steamy. Even though the latitude was pretty close to what it is now, there were palm trees and crocodilians.

MB: Where pine trees and grizzly bears live today! That shows the power of greenhouse gases to govern climate. Somehow, long before fossil-fuel burning humans existed, gases from hydrocarbons were released in immense volumes. One possibility is that magmas erupting from the rift that opened the north Atlantic Ocean ignited coal beds. Another possibility is that massive amounts of methane were belched from the seafloor.

Green River: Well, I can’t pin down the source of all that CO2, but I can give you a quantitative estimate of its concentration in the atmosphere. My beds include a rare sodium bicarbonate mineral that only forms from evaporating waters when carbon dioxide levels are greater than about 700 parts per million.

MB: Wow — 700 ppm! That’s much higher than our current value of 425 ppm, and we humans evolved in a world where CO2 concentrations had never exceeded 350 ppm. Today, unfortunately, we’re hurtling toward your number.

Green River: Thanks to some of my own coal seams and oil shale.

MB: Yes, the irony. Those who don’t know the geologic past are doomed to repeat it.

Green River: We haven’t really talked about the tectonic upheavals I saw. My lakes formed in the shadow of some of the great mountain ranges raised in my time — the Wind Rivers and Uintas.

Even as the mountains were growing, erosion tried to tear them down, and thick piles of sediment accumulated between the ranges, including in my lake basins.

MB: And erosion “unburied” everyone else here, making all of you accessible to those of us who live at Earth’s surface now. I’m grateful — otherwise we’d never have met.

Green River: Yes, it was exciting to see so many great rocks reappear, out in the elements being eroded again, perhaps becoming part of new formations. Coming full circle!

MB: Ah, that’s a nicer perspective: Those who know the geologic past are blessed to repeat it.

Nearly 50 million years later, northwestern Wyoming experienced a round of explosive volcanic activity as the region drifted over a “hot spot” — a rising plume of semi-molten rock — in Earth’s mantle. Three massive eruptions created what is now Yellowstone National Park. The Huckleberry Ridge Tuff formed during the first and largest of these events.

Huckleberry Ridge Tuff

ashes, ashes

Age: ca. 2.1 million years (Pleistocene Epoch)

Exposure: Yellowstone National Park

Huckleberry Ridge: I guess I’m the youngster here, barely a rock, made almost entirely of volcanic ash. I’m the yellow stone of Yellowstone. As the product of an infamous “supervolcano,” I’m viewed like a supervillain in a comic book. People are both fascinated and horrified by me — but they also don’t quite believe that I’m real.

In the eruption that formed me, the ash column reached 30 miles into the atmosphere, emptying the magma chamber and leaving behind a giant depression, the Yellowstone caldera. The total erupted volume was almost 600 cubic miles. Two other massive eruptions followed in the next million and a half years. A recurrence, which is possible, would completely shut down all human activity in the midcontinent. It would be bad.

To be candid, however, I think you humans have more immediate concerns to attend to. I came into being during the last ice age, and have seen my share of climate oscillations. But the rapidity of changes in the past hundred years scares me — and I’m the supervillain!

MB: Thank you for your frankness; it’s pretty sobering. And sincere thanks to the whole group. I’m deeply grateful to everyone for sharing your stories. So many Wyomings past, still very much present! It’s a comfort and joy to feel your enveloping company — worlds within worlds. You remind us that landscapes aren’t timeless — they’re timeful.

The history you tell of is thrilling: continents forming and breaking up, oceans coming and going, ecosystems rising and falling, never-ending cataclysm and rebirth, the world continuously remaking itself.

But it’s hard to know what to make of these narratives. Given everything you have seen over time, what advice can you give us humans? We are trapped in broken systems of our own making, paralyzed by discord and disillusionment. We’re not sure how to know what is true anymore. Can you help?

Hello — is anyone there?

Have I been talking to myself?

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This article appeared in the January 2026 print edition of the magazine with the headline “10 Wyomings.”

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Marcia Bjornerud, professor of geosciences at Lawrence University in Wisconsin, studies the physics of earthquakes and mountain building. Her books for popular audiences include Reading the Rocks, Timefulness, Geopedia and Turning to Stone.