In the vast flatness of the Sacramento Valley, encircled by a gravel mine, a gun shop, a fancy duck-hunting club, a Dollar General, a restaurant called Taco Time, several hundred gas wells, and a million billion almond trees, sit the remnants of a tiny volcano.
Tiny by volcano standards. The Sutter Buttes are 10 miles wide and poke up 2,000 feet. In classic butte fashion, they are steep on the sides. Nearly all of the rocks out here (and a considerable number of the decorative rocks in Sacramento, about an hour’s drive south) have their origins in this volcano. In front of Taco Time, someone has set out a semicircle of rust-colored andesite chunks that the volcano burped out, presumably meant to discourage cars from parking too close to the picnic table. Rocks can be hard to come by in the Central Valley, where nearly everything is covered by river sediments.
In a 50-mile-wide, 400-mile-long valley, the Buttes look improbable, a cartoon splat compared to the Coast Range to the west (tall, majestic) and the Sierra Nevada to the east (also majestic, even taller).
Nonetheless, the Buttes exist. How did they get there?
We awoke before dawn and drove to a strip mall at the edge of Yuba City in search of an answer.
The geology most of us learn about in elementary school tends toward neat, easily diagrammed layer cakes of stone. The Grand Canyon, split down the middle by the knife of the Colorado River, is one such cake. The Sutter Buttes are more like a cake that a showgirl has burst out of. It is spectacular, but it is a mess. Some of it appears to have been thrown around. There’s some weird stuff in the cake, like a quarter-mile of Cretaceous granite that seems like it came from the basement of the Sierras. The showgirl is, in geological terms, a bunch of superheated gas, so trying to track her down is inadvisable. Also: she jumped out of the cake between 1.6 and 1.4 million years ago.
In rock terms, 1.6 million years is a baby. Among the California drama that happened, geologically, before this baby was born: The Farallon tectonic plate began crawling underneath the North American tectonic plate, creating a range of volcanoes and underground chambers of hot magma that became the Sierra Nevada (215 to 75 million years ago). The Pacific Ocean reached all the way to the base of the Sierra (50 million years ago). The Pacific and the North American tectonic plates smashed into each other so hard that they (helped somewhat by sediments carried downstream from the Sierra and the Klamath Mountains) raised the Sacramento Valley to just above sea level (20 million years ago). Later, intense rubbing action between those two plates along the San Andreas Fault uplifted the Coast Range (5 million years ago).
But volcanoes have been volcano-ing, generally, for even longer. Back when this planet first solidified, 4.6 billion years ago, out of radioactive space rocks smacking together, continents weren’t part of the picture. We have the volcanoes that heaved up silica-rich magma to thank for our precious continents, and for their persistent and continuous tweaking of our landmasses. Even this baby of a volcano is a bit of a landscape engineer.
We arrive at the strip mall one morning in November right on time, and over a million years too late. Tule fog hangs around us, thick and opalescent. Shadows ahead resolve into several dozen people comparing hiking footwear. Some have been trying for years to snag reservations for a Buttes outing.
It is possible to spend your whole life near the Sutter Buttes and never actually set foot on them. The people who own most of it and control access to the roads in and out began closing them off in the 1960s. These days, most outsiders are escorted by guides affiliated with Middle Mountain Hikes, a local nonprofit. Ours is a rangy, acerbic geologist, an emeritus professor at California State University, Sacramento, named Brian Hausback. He began his quest to understand the volcano in the ’80s.
“Was it ever tough for geologists to get in here?” someone asks.
“Oh, it’s always been tough for everybody,” Hausback says.
Our group forms a convoy and trundles out. The landscape shifts to rows of almond trees, then, abruptly, a dirt road.
There are four locked gates ahead. At each one, Hausback jumps out of his white Land Cruiser, unlocks it, waits for the convoy to pass, and locks it again. We pass olive trees, beehives stacked like filing cabinets, hawks perched on power lines. The olive trees become tall grasses, backlit iridescent as the sun burns off the fog. Boulders appear strewn among them, as if a giant got lazy with her toys. We’re still at least a mile away from the initial explosions and extrusions that created the Buttes. These boulders were probably carried here by cold lahars—wet avalanches of mud, rocks, and other debris carried by heavy rainfall.
Beyond the fourth gate are several muscular cows, red with white faces, standing among Frisbee-size cow patties and staring at the group impassively. The cows weren’t here a few weeks ago, when Hausback was dressed as a zombie for the annual Haunted Hike in the Buttes. The heat and lack of year-round water keep vegetation on the Buttes sparse and scrappy, a situation that is bad for cattle, but good for looking at rocks.
At the trailhead, Hausback unfurls several maps and diagrams, pinning them to the side of the Land Cruiser with magnets. The vehicle is now a display board. Class is in session.
The layer cake of the Sutter Buttes erupted over hundreds of thousands of years. Some of these were showgirl-scale events, some were more modest. First came the rhyolite—oozy, silica-rich balloons of magma from beneath the earth’s crust. They traveled upward through the many layers of sediment that had been pressed into sedimentary rocks, past the sediment waiting to become rocks, and burst through the surface like a heavy metal album cover as lava domes—glowing spires of incandescent hot rock, anywhere from a few hundred feet to half a mile in diameter.
Geology is like cooking. The same few ingredients lead to dramatically different outcomes depending on how they are put together. Magma that percolates through the earth’s crust but declines to erupt, staying cozy in a cocoon of other rock like pit barbecue, becomes granite. Magma that comes out hot and cools down fast becomes obsidian.
Rhyolite is between those two, bubbling up from the earth in juicy blobs that solidify and crystallize as they reach the earth’s surface. In their mildest state, they flop on top of each other like wads of dough and cool into chubby hot cross buns of rock that are both impossibly cute and deadly, because they are prone to explode. While they’re liquid, their viscosity traps bubbles of hot gas and chemicals—time bombs that can burst open if magma keeps pushing its way out through them. As rocks of the Sutter Buttes go, rhyolite happens to be Hausback’s favorite. “Beautiful rock,” he says, holding up a glossy white chunk like it’s a prized terrier puppy.
Explosions of rhyolite first shaped the Buttes (left). Then came the andesites, which start gray (center) and turn reddish (right) when exposed to air.
The next rock layers to erupt, Hausback says, were mostly andesite. Andesite is named after the Andes, but it’s common everywhere you find volcanoes. To bake some andesite, just mix your magma with some basaltic seafloor and just the right proportions of minerals on its journey up to the surface. At the Buttes, andesite extruded itself into domes, and it did so with such abandon that it pushed slabs of sedimentary rock up from a mile beneath the Central Valley, tilting them, and their collection of Cretaceous-period marine fossils, into view.
Marine fossils, because most of California put in some long millennia as the floor of the Pacific Ocean, though the Buttes themselves are too young to have personally experienced this. “Everything,” says Hausback, “is older than this volcano.”
Humans have been around for about 300,000 years. The practice of looking closely at rocks to see if they contain anything dangerous or useful has probably been around for about that long. In the 1920s, a UC Berkeley geology professor named Howel Williams began mapping the Sutter Buttes, trying to reconstruct what had happened there. Being British, Williams was partial to castle terminology. The andesite and rhyolite lava domes that made up the buttes he dubbed the “castellated core.” The soft sedimentary rock pushed to the surface that had eroded down to a soft, lush landscape was the “moat.” The low, sloping hills encircling the castle and moat were the “ramparts.”
In 1895, a geologist named Waldemar Lindgren had correctly attributed the cake to a volcano. Williams effectively diagrammed it. Another geologist, Garniss H. Curtis, worked with Williams to figure out how old it was. But further specifics of how it got that way remained a mystery.
Hausback got roped into the mystery through Curtis, who was a mentor. One of Hausback’s first jobs as a geologist involved getting dropped off by a helicopter into the crater of the recently erupted Mount St. Helens, in Washington state, to catalog the new landscape created by the collapse of the north side in 1980. When he began the mapping, in 1987, lupine was revegetating the mesa, and the streams coming off the mountain were warm from continued volcanic activity.
A few years later, Curtis suggested that Hausback investigate the Buttes, on the grounds that, unlike Mount St. Helens, they were right next to Sacramento. Hausback contacted one of the ranchers through a friend. That rancher was skittish about visitors, but put him in touch with another rancher (also not interested), who connected him with a different rancher, who liked the idea of having a geologist stop by.
When Hausback got there, he immediately saw that the Buttes eruptions had been far more explosive than anyone had realized.
To get to the drama, the group hikes out of the moat. The cows decline to follow. When the mood strikes them, they’ll go way up onto the domes in search of adventure, but generally they, and most of the plants, stick to the moat. That’s where most of the sediment is and therefore the good life—a narrow belt of Central Valley–like lushness in this rocky environment. There’s marine sediment around here going back 80 million years or so, says Hausback, while trying to entice someone—anyone—to jump into a boot-sucking wallow left by a feral pig, possibly the same pig that was seen tearing through the grass like a bullet train earlier. But the sediment tipped up to the surface by the volcano is “the youngest of the old stuff,” he says.
We hike up steep terrain to gaze at even steeper terrain—a little vertical cliff emerging from the grassy hillside that looks like our giant took a large dose of psychedelics and cemented massive blocks of andesite together. This is what Hausback calls a “rocky soufflé”—a pyroclastic flow, like what happened at Mount St. Helens.
The soufflé is embedded with signs of dramas past. Many of the blocks of andesite are cracked into prismatic patterns, a sign that they cooled rapidly from a high temperature. Samples drilled out of this flow show that all the rocks in this soufflé are magnetically aligned, meaning that the magnetite within them heated to at least 580 degrees Celsius, forgot their previous magnetic loyalties, and settled into a new alignment together when they cooled.
But still, why did a volcano happen here? The likeliest culprit, Hausback says, is a wedge of geologic chaos known as the Mendocino Triple Junction—the ever-moving junction between the Pacific and North American tectonic plates, and the last fragments of the Farallon plate. This threesome first met about 30 million years ago outside what is currently known as Los Angeles and has been moving north since then, leaving volcanoes (and the San Andreas Fault) in its wake: first Morro Rock, then Pinnacles, then the volcanic rocks of the Berkeley Hills, which are now part of Sibley Volcanic Regional Preserve, then Mount St. Helena and the Sonoma Volcanics, followed by the Burdell Mountain Volcanics near Petaluma and the Clear Lake Volcanics.
The Buttes may not be as lonesome as they look, at least underground. Recently, some geologists spotted something in a new map, which was made by the U.S. Geological Survey while prospecting for groundwater storage. The map shows a thin red slash of highly magnetic something—a clear line separating two types of rock—that runs up through the middle of the Central Valley, including the Buttes: an old fault zone. Hausback suspects it’s a buried offshoot of some Mendocino Triple Junction drama. There’s an area near Moon Bend, in Colusa, where whatever is down there almost broke through. What we’re standing on might just be the only volcano that made its way to the surface.
The group hikes back over the rampart and into a glen of blue oak trees. Their presence, says Hausback, are a sign that the rock here has been relatively stable: All the trees are mature, and none of them are tilted at weird angles.
“So how old do blue oaks live?” someone asks.
“I think three hundred years?” says Hausback, dismissively. “Not very long.”
Some of the trunks have a thick coating of mud at knee height, from feral pigs scratching themselves. Barbados sheep have gone wild out here, evading capture in the steep terrain. There was free-range methane, too, left when ancient foraminifera—single-celled protists that hang out in ocean sediment—decomposed into methane. The methane would work its way up to the surface and sometimes ignite during wildfires, lighting the Buttes with an eerie glow. In the late 1800s, someone sank a shaft into a patch of butte and lit a candle at the bottom, creating an impromptu 24/7 Bunsen burner. People would come out and picnic around it.
At the end of the hike, Hausback takes the group to look out over the edge of the private land where we’ve been hiking today into Peace Valley, about 1,700 acres that the state bought in 2003 with the plan of turning it into a state park.
This has been hard to do without publicly accessible roads. For now the existence of the park as a public good is, mostly, a website that says that the park is not open, except for guided hikes during events like the Snow Goose and California Swan festivals. Sutter Buttes State Park is not even its official name. “The name of the park was not determined,” it reads, “until more information could be obtained on the various names and historical events associated with the site.” That was 21 years ago.
Humans, who have been around the Buttes for at least 10,000 years, are one of the few things younger than this volcano. Hausback has seen arrowheads in the Buttes made of obsidian, which isn’t from here. It was likely harvested from Glass Mountain in Napa. Near the overlook, the group passes a waist-height boulder, shaded by the oaks. Someone marvels at it, but Hausback declines to identify it, on the grounds that “it’s got biology all over it,” before declaring it andesite.
On top of the boulder is a smooth divot, about the size of a fist. Someone, who knows how long ago, carved a mortar into it for grinding acorns. Someone who, like the arrowhead-maker, had their own practical interest in geology.
SIDEBAR
The Many-Named Buttes
During the Gold Rush, the Buttes were known as the Marysville Buttes. In 1949, the Yuba City Women’s Club persuaded the U.S. Board on Geographic Names to rename them the Sutter Buttes—after John Sutter, a Swiss guy who in the 1840s had sweet-talked the governor of Mexican California into giving him several large chunks of land, including one south of the Buttes.
To white residents during Sutter’s time, he was a roguish but generous scoundrel who liked to party a little too much. To the Maidu, Yokuts, Concow, Nisenan, and other Indigenous groups who lived in the valley then, Sutter was a spectacular asshole who financed his champagne dreams in part by selling local children into slavery.
It’s likely the Buttes will be renamed, although it’s not clear to what. In 2024, a new petition was filed to call the formation the Sacred Buttes (the Buttes figure prominently in local spiritual lore, sometimes as a passage to the afterlife, sometimes as a meeting place for untrustworthy deities).
Last year, with the previous request still undecided, the Nevada City Nisenan petitioned to change the name to Middle Mountain—the English translation of Estom Yanim, the Nisenan name for the Buttes. The group would also accept “Spirit Mountain,” “Sacred Mountain,” “Sacred Buttes,” or even “Marysville Buttes,” on the grounds that even naming the buttes after a Gold Rush town that was itself named after some white guy’s wife is better than calling them “Sutter.”
EXPLORE
Sutter Buttes
Sutter Buttes is mostly private ranchland. Public access is controlled by Middle Mountain Interpretive Hikes, which offers group hikes from late October through April. Tickets are $45–$55 and fill up quickly; stalk them on MiddleMountainHikes.org. Details like meeting places are emailed to ticket holders.
- The draw: A small, extinct volcano all by its lonesome in the Great Valley that wears its geological history on its sleeve. Plus ranchland, wildflowers (in the spring), stargazing, and the occasional feral hog.
- Trails: No groomed trails. Wear closed-toe hiking shoes, layer up, and consider bringing poles. Hikes range in difficulty.
- Facilities: Porta-potties. Bring more food and water than you think you might need.
- Accessibility: No wheelchair-friendly paths.
- Getting there: By car, 119 miles northeast of Berkeley.
