Unearthing the Secrets of the Sierra Nevada Batholith

An example of Sierra Nevada batholith. There are several domes in Yosemite besides Half Dome. (Erik Olsen)

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Ansel Adams, with his iconic black-and-white photographs of Yosemite and the Sierra Nevada, likely never realized that his lens was capturing not just breathtaking landscapes but one of geology’s most fascinating phenomena—the Sierra Batholith, a colossal formation of granite that lies at the heart of the mountains he immortalized. The Sierra Batholith is a massive granite body that reveals the tale of ancient volcanic activity in California, showcasing nature and time as master artists, and the slow tectonic forces that have shaped the Earth’s crust over millions of years.

Discussing the Sierra batholith, the writer John McPhee wrote: “It lies inside the Sierra like a big zeppelin. Geologists in their field boots mapping outcrops may not have been able to find a bottom, but geophysicists can, or think they can, and they say it is six miles down. If so, the batholith weighs a quadrillion tons, and its volume is at least a hundred and fifty thousand cubic miles.”

The Sierra Batholith is unique because it represents a massive, exposed section of the Earth’s continental crust formed deep underground during the Mesozoic era, between 85 and 220 million years ago. Unlike typical mountain ranges that form through surface processes, the Sierra Batholith was created as molten rock, or magma, cooled and solidified far beneath the Earth’s surface.

A batholith is a gargantuan underground rock formation made up mostly of intrusive igneous rock, predominantly granite.” Intrusive” in this context doesn’t mean the rock is barging into conversations—it refers to rock that formed beneath the Earth’s surface as molten magma slowly cooled and solidified. The Sierra Nevada batholith is a titan among batholiths, covering an area of about 40,000 square kilometers (16,000 sq. miles).

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How did this underground monolith come into being? Picture the Earth’s crust as a sort of geological lasagna, consisting of multiple layers of rock. When the Pacific Plate and the North American Plate crashed into one another—intense pressure and heat accumulated deep within the Earth. The result is the formation of magma, which then cooled and solidified slowly below the Earth’s crust. The slow cooling allowed minerals to crystallize, creating a texture in the rock that’s coarse and beautifully patterned—not unlike granite countertops for your kitchen, but on a monumental scale.

The Sierra Nevada Batholith was only revealed after vertical miles of Earth’s crust above it eroded away. Stretching from just north of Lake Tahoe to Tehachapi Pass, this massive formation resembles an air mattress—450 miles long, 60 miles wide, and about eight to nine miles thick, with six miles still buried underground and two to three miles towering above the surrounding landscape. The sheer size, scale, and immense mass are awe-inspiring—and it’s all right here in California.

This creation process was far from uniform—the batholith is actually not a single mass, per se, but a cluster of blobs of molten rock fused at the edges. These blobs, called plutons, are clustered together like cobblestones in a street or the uneven domes of a bubble wrap sheet. What we now see are the rounded tops of about 20 oval-shaped plutons, each around 10 by 20 miles in size. Chemically, each blob varies slightly. Granite, made mostly of silica, which forms 60 to 80 percent of its mass, gets its whitish hue from silica, with black flecks of feldspar and hornblende, sometimes tinged with reddish iron oxide. The slower the cooling, the more time quartz crystals had to form.

One of the largest and youngest plutons in the Sierra is called the Whitney Intrusive Suite, and it is the foundation of the nation’s tallest peak outside of Alaska, Mt. Whitney.

A geologic map of Yosemite National Park showing the many intrusions that make up this part of the Sierra Nevada Batholith.

Natural forces like wind, water, and glaciers have gradually eroded the Earth’s surface, exposing the underlying granite. Imagine the work of an infinitely patient sculptor, slowly chipping away at a block of marble year after year, century after century. Except here, the sculptor is Mother Nature, and the time frame is geological, spanning epochs rather than mere decades or centuries.

One fascinating facet of this story is how glaciers have been among the most dramatic artists in nature’s magnificent art gallery. Their slow, relentless movement sculpted features like Yosemite Valley, one of the most breathtaking landscapes on Earth.

Half Dome in Yosemite, a granite giant of the Sierra Batholith, showcases millions of years of cooling magma and erosion. (Erik Olsen)

But the Sierra Nevada batholith isn’t just a stationary slab of rock—it’s also a dynamic part of California’s ecosystem. The granite affects the way water moves or stagnates in the region, influencing local hydrology and, by extension, water supply. When the snow in the Sierra Nevada mountains melts, it feeds rivers and lakes, many of which are essential to California’s agricultural and urban areas. Imagine the batholith as a silent but vital cog in the wheel of California’s complex water system.

One excellent resource to learn more about the Sierra and the Sierra batholith is Kim Stanley Robinson‘s The High Sierra: A Love Story. The book is an evocative blend of memoir, natural history, and environmental meditation, centered around the Sierra Nevada mountains, a region Robinson has deeply cherished for decades. Robinson, widely regarded as one of today’s greatest science fiction writers, has authored numerous books on topics ranging from space exploration to climate change. Yet one of his deepest passions is hiking in the Sierra.

Half Dome, carved from the granite of the Sierra Batholith, offers a glimpse into Earth’s deep history, where ancient magma chambers solidified beneath the surface and were gradually revealed through uplift and erosion. (Erik Olsen)

In the book, he explores the geologic grandeur, ecological richness, and personal significance of this mountain range, offering readers a vivid portrayal of its granite peaks, alpine meadows, and glacial valleys. Robinson intertwines his own hiking experiences with reflections on the Sierra’s geological formation, the indigenous histories of the land, and the environmental challenges it faces today. His narrative is as much an ode to the beauty and solitude of the Sierra as it is a call for greater environmental stewardship, showcasing his talent for combining science with a profound emotional connection to the natural world. (If you haven’t yet read one of his books, you should. Start with Red Mars.)

Sierra Nevada from Lone Pine (Erik Olsen)

If you’re the adventurous type with a penchant for rock climbing or hiking, the Sierra Nevada batholith serves as both your playground and your classroom. Whether you’re scaling the granite walls of El Capitan or hiking the trails near Lake Tahoe, you’re traversing a landscape that’s millions of years old. Each crevice, each outcrop, and each boulder tells a tale of geological drama spanning eons.

The Magic, Wonder, and Science of Ocean Bioluminescence in Southern California

How and why so many of earth’s creatures make their own light.

Bioluminescent waves in Southern California

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Last month, a video went viral showing a small pod of dolphins swimming at night off the coast of Newport Beach. Seeing dolphins off Southern California is not particularly unusual, but this was a very special moment. In the video, the dolphins appear to be swimming through liquid light, their torpedo-shaped bodies generating an ethereal blue glow like a scene straight out of Avatar. The phenomenon that causes the blue glow has been known for centuries, but that in no way detracts from its wonder and beauty. The phenomenon is called bioluminescence, and it is one of nature’s most magical and interesting phenomena.

A Caridean shrimp, *Parapandalus* sp., enveloped in bioluminescent spew emitted during an escape response. *(NOAA/OER)*

Bioluminescence is the production and emission of light by a living organism, and it is truly one of the great magical properties of nature. At its core, bioluminescence is the way animals can visually sense the world around them. It’s all built on vision, one of the most fascinating and useful senses in the animal kingdom. Seeing is impossible without light, and so it makes sense that in the absence of sunlight, some animals created a way to make their own light.

I have been fascinated by bioluminescence since I was a child growing up near Newport Beach when the occasional nearshore red tide bloom would illuminate the waves like a high tech LED light show. It’s a truly magical experience. I’ve also experienced bioluminescence in various places around the world, including Thailand, Mexico, and Puerto Rico. In fact, 13 years ago, I made the trip to Puerto Rico’s Vieques Island and its world-famous Mosquito Bay, for the sole purpose of seeing the bay in person and swimming and kayaking in its warm, glowing waters (there is a rental outfit there that does tours at night…it’s amazing. Trust me.)

The phenomenon of bioluminescence is surprisingly common in nature. Both terrestrial and sea animals do it, as do plants, insects (for example, fireflies), and fungi. Curiously, no mammals bioluminesce. That we know of, although several species fluoresce, which is when organisms absorb light at one wavelength and emit it at another, often under ultraviolet (UV) light. The platypus is an example. But the ocean is definitely the place that animals and plants bioluminesce the most. Which makes sense because deep in the ocean, there is little or no light. Light is absorbed very quickly in the water, so while on land you might be able to see a single streetlight miles away, after about 800 feet, light largely disappears in the depths of the ocean. I know. I’ve been there.

It’s estimated that nearly 90 percent of the animals living in the open ocean, in waters below 1,500 feet, make their own light. Why they do this is in part a mystery, but scientists are pretty sure they understand the basic reasons animals do it: to eat, to not be eaten, and to mate. In other words, to survive. And to communicate.

The angler fish dangles a lighted lure in front of its face to attract prey. Some squid expel bioluminescent liquid, rather than ink, to confuse their predators. A few shrimp do too. Worms and small crustaceans use bioluminescence to attract mates. When it is attacked, the Atolla jellyfish (Atolla wyvillei) broadcasts a vivid, circular display of bioluminescent light, which scientists believe may be a kind of alarm system. The theory is that the light will attract a larger predator to go after whatever is attacking the jellyfish. While this is still a theory, a 2019 expedition that took the very first images of the giant squid used a fake Atolla jellyfish designed by the scientist Edith Widder to lure the squid into frame. I had the fortune of interviewing Dr. Widder, one of the world’s top experts on bioluminescence, several years ago for the New York Times.

Edith Widder holds a vial of bioluminescent plankton. Credit: Erik Olsen

Making light is clearly beneficial. That’s why, say evolutionary biologists, it appears that bioluminescence has arisen over forty separate times in evolutionary history. The process is called convergent evolution and is the same reason that bats and birds and insects all evolved to fly independently. Clearly, flying confers a major advantage. So does making light.

While the Internet is awash in images of bioluminescent creatures, very often the term is confused with fluorescence (mentioned above). Even reputable science organizations sometimes do this. Bioluminescence is not the same thing as fluorescence. Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. Many animals like scorpions and coral fluoresce, meaning that they appear to glow a bright otherworldly color when blue light is shone on them. The key idea here is that the animals are not generating their own light, but rather contain cells that reflect light in fluorescence.

Fluorescent (not bioluminescent) scorpion in Baja California, Mexico. Credit: Erik Olsen

So what about the recent explosion of bioluminescence in Southern California? The light we are seeing is made by tiny organisms, type of plankton called dinoflagellates (Lingulodinium polyedra) that occasionally “bloom” off-shore. Often, this is the result of recent storms that bring tons of nutrient-laden runoff into the ocean. The tiny plankton feed on nitrogen and other nutrients that enter the ocean from rivers and streams and city streets. A lot of the nutrients come from California’s vast farms, specifically the fertilizer used to grow California’s fruits and vegetables. With all that “food” coming into the ocean system, the algae rapidly multiply, creating red tides, or vast patches of ocean that turn dark brownish red, the color of pigment in the algae that helps protect it from sunlight. Michael Latz, a scientist at Scripps Institution of Oceanography at UC San Diego, says that the animals use bioluminescence as a predator avoidance behavior.

Sometimes red tides are toxic and can kill animals and make people sick who swim in the ocean. (That does not appear to be the case in California right now). At night, when they are still, the animals can’t be seen. But when the water is disturbed, which adds oxygen into the mix, a chemical reaction takes place in their bodies that causes luciferin (from the Latin lucifer or ‘light-bearer’) to oxidize and becomes catalyzed to make luciferase, which emits photons or particles of light. It’s not understood exactly how or why this happens, but we do know there are many kids of luciferase. In fact, scientists know the genes that create luciferases and have implanted them into organisms like mice, silkworms, and potatoes so that they glow. They’ve made bioluminescent plants, too. An Idaho-based start up called Light Bio, in fact, sells bioluminescent petunias that you can purchase.

Light Bio’s genetically engineered petunias glow green thanks to DNA added from bioluminescent mushrooms. Photo (Light Bio)

Perhaps the most magical thing about bioluminescence is that it doesn’t create heat. Almost all the lights we are familiar with, particularly incandescent light, like that from generic light bubs, generate a tremendous amount of heat. Of course, we have learned how to make this heatless chemical light ourselves, easily experienced when you crack and shake a glow stick, mixing together several chemicals in a process similar to the one animals in the ocean use to create bioluminescent light. But the light from glow sticks is not nearly strong enough to illuminate your back yard. In the last few decades, we’ve learned how to make another kind of light that produces little heat: LEDs. Though the process is very different, the concept is the same: talking a molecule or a material and promoting it to an excited state. Where electricity is used, in the case of LEDs, it’s called electroluminescence, where it’s a chemical reaction it’s chemiluminescence, of which bioluminescence is one form.

Whether you are a religious person or not (I’m not) it’s no coincidence that one of the first things God said was, “Let there be light!” Light and light energy give us plants and animals to eat, and allows us to see. It heats our world, it fuels our cars (oil is really just dead organic material compressed over time, and that organic material would not have existed without sunlight). While some animals deep in the ocean can live without light, most of us cannot. And it’s a rather astounding feat of nature than when there is no light, many of the earth’s creatures have evolved to produce it themselves. If you don’t believe me, just go down to the Southern California shore in the evening when there is a red tide. Leave your flashlight at home. You won’t need it.

The Lost Island of Santarosae off California’s Coast

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Imagine a massive island off the coast of California roughly thrice the size of Maui, a lush and wild place where miniature mammoths once roamed and ancient humans hunted in the shadows of towering trees. This island once existed and it’s called Santarosae, and while it is gone now, it was once a thriving ecosystem, teeming with life. Its story provides a captivating window into the ever-changing natural history of the California coast region.

During the last Ice Age, approximately 20,000 to 25,000 years ago, when sea levels were significantly lower, Santarosae Island was a single, expansive landmass that now comprises most of California’s Channel Islands. As the cooler Pleistocene climate transitioned into the warmer Holocene (the epoch we are in now), the Earth’s oceans heated and expanded. Continental ice sheets and glaciers melted, releasing vast amounts of water and causing sea levels to rise dramatically.

At its peak, Santarosae was massive—four of today’s Channel Islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa) were all connected into a single landmass. It spanned around 1,500 square miles, making it a significant feature of the Pacific coast landscape. Today, only remnants remain in the form of those four separate islands, but evidence of Santarosae’s ancient past continues to reveal itself to scientists.

Map depicting the reconstructed geography of Santarosae.

Anacapa was the first to break away, around 10,300 to 10,900 years ago, as rising waters gradually submerged the narrow isthmus that once connected it to the rest of Santarosae. This slow disintegration of the super island was witnessed by the humans already inhabiting the region. Having arrived between 12,710 and 13,010 years ago, possibly even earlier, these early settlers likely traveled by boat, following the “kelp highway“—a rich, coastal ecosystem of underwater seaweed forests stretching from northern Japan and Kamchatka, along the southern shores of Beringia, down the Pacific Northwest, and into Baja California. For these early explorers, Santarosae would have appeared as a land of abundant resources.

One of the island’s most captivating features was its population of pygmy mammoths, found exclusively on Santarosae. Standing between 4.5 to 7 feet tall at the shoulder and weighing around 2,000 pounds, these miniaturized versions of mainland Columbian mammoths were about the size of a large horse and evolved to suit their isolated island habitat (see our story on the island biogeography of the Channel Islands). The reasons for their dwarfism stem from a phenomenon called island rule, where species on islands often shrink due to limited resources and isolation, as well as a shortage of predators. Despite their smaller size, these island-dwelling mammoths likely shared many characteristics with their larger relatives, including a similar body shape, short fur, and a large head. These mammoths roamed Santarosae until they disappeared around 13,000 years ago, coinciding with both climate changes and the arrival of humans.

Pygmy Mammoth excavation on the Channel Islands (NPS)

The first discovery of “elephant” remains on Santa Rosa Island was reported in 1873. Over time, additional excavations provided insight into the island’s mammoth population, which gradually became smaller over generations, eventually disappearing at the end of the Pleistocene. Notably, paleontological digs conducted on Santa Rosa Island in 1927 and 1928 unearthed the remains of a new species, Mammuthus exilis. In the 1940s and 1950s, Philip Orr of the Santa Barbara Museum of Natural History recovered further specimens while conducting archaeological and geological work on the island.

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Most pygmy mammoth remains have been discovered on Santa Rosa and San Miguel Islands, with fewer finds from Santa Cruz Island and even fewer from San Nicolas Island, which lies outside the Channel Islands National Park.

Santarosae was not just a wilderness for megafauna—it was home to some of the earliest known human settlers in North America. Archaeological discoveries, such as the remains of a 13,000-year-old woman unearthed on Santa Rosa Island, point to a sophisticated maritime culture. These ancient humans, likely ancestors of the Chumash people, navigated the waters around Santarosae in plank canoes, hunting seals, birds, and fish, while gathering plants and shellfish.

Archaeologists excavate a anthropological site at the Channel Islands (NPS)

The island provided ample resources, but it wasn’t isolated from the rest of the world. The people of Santarosae were part of a complex trade network that stretched across the California coast. Evidence of these connections can be seen in the tools and materials found on the island, some of which came from distant sources. As sea levels rose, however, these early inhabitants had to adapt to the shrinking island, eventually migrating to the mainland.

Santarosae’s landscape during the Ice Age was strikingly different from what we see on today’s Channel Islands. Dense forests of pines, oaks, and other vegetation covered much of the island, supporting a rich diversity of life. The island’s topography included hills, valleys, and freshwater sources, offering an ideal environment for both humans and animals. As the climate warmed and sea levels rose, the island’s ecology shifted. Forests retreated, and the landscape began to resemble the wind-swept, scrubby terrain seen on the modern Channel Islands.

The rise in sea levels didn’t just transform the landscape; it also altered the ecosystems. Many of the animals, like the pygmy mammoths, couldn’t survive the changing conditions (or human hunters), while new species adapted to the shrinking landmass. Birds, insects, and plant species began to dominate, and the island ecosystems became more specialized.

Today, the remnants of Santarosae offer an invaluable window into the past. The Channel Islands National Park protects much of the area, and researchers continue to uncover clues about the island’s history. Ongoing archaeological digs and ecological studies on the islands help piece together the story of Santarosae’s people, animals, and landscape.

Tourists now enjoy the natural beauty of the Channel Islands (Erik Olsen)

For those who visit the Channel Islands today, it’s hard to imagine the ancient world of Santarosae—a much larger island teeming with life. But the remnants of this lost island still hold secrets waiting to be uncovered, offering a fascinating glimpse into California’s distant past and a reminder of how the forces of nature continually reshape our world.

Though Santarosae is now submerged, its influence is still a significant part of California’s natural history.

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New Research Sheds Light on the Saber-Toothed Cats of California, Fierce Predators of the Pleistocene

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Around 15,000 to 20,000 years ago, the landscape near present-day Los Angeles was a diverse mix of environments shaped by the end of the Ice Age. Cooler and wetter than today, it was dominated by savannah-like grasslands, wetlands, and patches of dense forests filled with towering oaks and pines. Prehistoric rivers and lakes dotted the landscape, nourishing a rich ecosystem teeming with life. Massive herbivores like mammoths, giant ground sloths, bison, and ancient camels roamed these plains, foraging on abundant grasses and shrubs.

Among these creatures of the Pleistocene Epoch, predators like saber-toothed cats (Smilodon fatalis) ruled, using the cover of forests and brush to ambush their prey. These large cats thrived alongside other carnivores like dire wolves and American lions, each species carving out its niche. However, the landscape was in flux—warming temperatures gradually dried out the environment, increasing the frequency of wildfires and altering the balance of flora and fauna. As human populations expanded and hunted large herbivores, the delicate ecosystem began to unravel, setting the stage for the extinction of many of the region’s iconic megafauna (more on this later).

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Saber-toothed cats are some of the most iconic prehistoric predators to have roamed California. Known for their distinctive long, blade-like canine teeth, these powerful carnivores thrived during a time when much of North America was covered in ice and the landscape teemed with large herbivores. Fossils of these magnificent creatures have been found across the state, with an impressive concentration in the famous La Brea Tar Pits in Los Angeles, revealing a vast amount of details about their biology, natural history, and the world they lived in. In fact, thousands of skeletons are preserved in the Rancho La Brea Tar Pits, making it the largest and most significant site for studying saber-tooth cats and other Pleistocene-era animals.

But first, let’s clear up a few things. The terms “saber-toothed tiger” and “saber-toothed cat” are often used interchangeably, but they refer to different concepts, and the distinction is important for scientific accuracy. “Saber-toothed tiger” is a misnomer because these prehistoric animals were not true tigers, nor were they closely related to them. Instead, they belonged to a now-extinct subfamily of felines called Machairodontinae, with the most famous genus being Smilodon. Modern tigers, on the other hand, belong to the Panthera genus and are part of a completely different evolutionary line. The term “saber-toothed cat” is more accurate because it reflects the broader diversity of species in this group, not just a single “tiger-like” animal. This distinction is crucial because it prevents confusion in understanding the evolutionary history of felines and avoids spreading inaccuracies in the scientific and popular understanding of extinct species.

A great deal of modern research has been conducted on the saber-tooth cat, ranging from genetic studies to isotopic analysis, fossil reconstruction, and insights into their ecological role during the Pleistocene Epoch. In fact, in 2020 researchers from the University of Copenhagen mapped the entire nuclear genome of a sabre-toothed cat known as Homotherium. The genetic study revealed new insights about a socially intelligent pack animal, that specialized in endurance-based hunting over long distances.

The cover of the 1908 October issue of *Sunset* magazine.

When you look at the fossilized skeletons of saber-toothed cats on display at the La Brea Tar Pits, it’s easy to imagine these powerful predators silently stalking their prey through the ancient landscapes, ready to spring with sharp, curved teeth bared and bloody from an earlier meal. Their upper canine teeth were long, sharp, and curved like sabers, often reaching lengths of up to 7 inches (18 cm). Unlike the teeth of modern big cats, which are built for biting and holding prey, the saber teeth were relatively fragile and not ideal for crushing bones. This suggests that these animals had to be precise in how they used their teeth to kill.

Saber toothed cat skull at La Brea Tar Pits (Erik Olsen)

Rather than relying on brute force to clamp down on their prey, saber-toothed cats likely used their teeth to deliver deep, slashing wounds to vulnerable areas, such as the neck, throat, or belly of large herbivores. Some scientists believe that after overpowering their prey with their strong forelimbs, they would deliver a quick, lethal bite, severing major blood vessels or the windpipe. The killing technique of saber-toothed cats was likely specialized for large, slow-moving prey like bison, mammoths, or camels.

Saber-toothed cat (*Smilodon fatalis*). (Indiana State Museum)

This precision style of hunting contrasts with how modern big cats, like lions, use their teeth to bite and hold, crushing the windpipe or suffocating their prey. The saber-toothed cat’s teeth were well-adapted to slicing, but not to the prolonged grip needed for suffocation.

A recent study on saber-toothed cats from paleontologist Jack Tseng of the University of California, Berkeley, reveals that juvenile cats retained their baby teeth alongside their developing adult fangs, likely as a stabilizing mechanism. This double-fanged stage, lasting up to 30 months, helped protect the growing sabers from breaking as young cats learned to hunt. Through computer simulations and mechanical tests, researchers demonstrated that the baby tooth acted as a buttress, reducing the risk of saber damage during this critical learning phase. This finding offers new insights into the hunting development of these prehistoric predators.

The cranium of a *Smilodon* with fully-erupted sabers (Jack Tseng)

Modern research is uncovering potential new insights into the saber-tooth cat’s behavior, including possible hunting techniques, social structures, and interactions with other species. Paleontologists have found fossilized throat bones in Smilodon at the La Brea Tar Pits similar to those in modern big cats like lions and tigers, suggesting that these prehistoric predators may have also roared with powerful vocalizations.

One of the most fascinating debates surrounding Smilodon is whether they hunted alone or in groups. Further fossil evidence from the La Brea Tar Pits suggests that these cats may have lived and hunted in social groups, similar to modern lions. Many Smilodon skeletons show evidence of healed injuries, which has led paleontologists to believe that they may have cared for each other in social settings, allowing injured individuals to recover rather than being abandoned. This level of social cooperation would have been an important adaptation in a world full of dangerous megafauna, enabling them to take down larger prey.

Prehistoric scene with saber-toothed cat.

The extinction of saber-toothed cats, specifically Smilodon, in California has been a subject of extensive research. A study from 2023 published in the prestigious journal Science shows just how quickly the largest animals disappeared from the La Brea fossil record. Scientists from the La Brea Tar Pits, including a University of Oregon professor and postdoctoral researcher, employed a computer model to explore how factors like wildfires, climate change, species loss, and human presence interacted. This revealed a far more intricate explanation for the extinctions than earlier theories, which often pinned the blame on a single factor such as human overhunting or climate shifts. According to the study, humans likely played a pivotal role by driving herbivores to extinction, which in turn led to an overgrowth of vegetation, creating fuel for wildfires. At the same time, the climate was becoming drier, compounding the problem, and leaving carnivores without sufficient prey to survive.

**Sequence of ecological events as recorded at Rancho La Brea, California.** (Natural History Museum of Los Angeles County)

Although most of the existing fossils came from the La Brea Tar Pits in Los Angeles, Smilodon was widely distributed across North America, from coast to coast, reaching as far north as Idaho and Nebraska and extending south into South America. It is most famously associated with California and Florida. The oldest known fossil of Smilodon dates back approximately 500,000 years, while the youngest, discovered during bank construction in Nashville, Tennessee, is just 9,400 years old.

Saber-toothed cat fossil skeleton at La Brea Tar Pits (Erik Olsen)

The La Brea tar pits are a unique and incredibly fruitful outdoor laboratory for understanding animals from 50,000 years of the Pleistocene and the environment in which they lived. Paleontologists have unearthed thousands of Smilodon bones, providing a wealth of information about their anatomy and behavior. The bones show a high rate of injuries, including broken bones and bite marks, which supports the idea that these cats faced significant risks when hunting. In addition to Los Angeles, saber-toothed cat fossils have been found in various parts of California, including San Diego and along the Central Valley, though the La Brea Tar Pits remains the most prolific source.

Imagine that. One of the greatest fossil sites in the world lies amidst the skyscrapers and traffic-clogged streets of Los Angeles. It’s kind of mind-boggling.

Despite their extinction, the legacy of saber-toothed cats endures in the fossil record and in our imagination. Because of it’s ability to capture public interest, ane because the fossil record is so abundant and varied, Smilodon fatalis is now the state fossil of California, symbolizing the state’s rich prehistoric past.

Looking back at John McPhee’s Assembling California: A Journey through Geology and Time

Sierra Nevada Mountains and Hot Creek Geological Site (Erik Olsen)

California’s diverse landscapes, rich history, and abundant natural phenomena have inspired many scientific-themed popular books, ranging from John Steinbeck’s “The Log from the Sea of Cortez,” with its focus on marine biology, to Mary Austin’s “The Land of Little Rain,” a lyrical examination of California’s desert environment, not to mention the late Marc Reisner’s Cadillac Desert, an epic history of California’s contentious relationship with water. (I’ve read it twice.)

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But when it comes to exploring the state’s geology – its mountains, coastlines, and, most notably, its fault lines – few books can match the prowess and eloquence of John McPhee’s “Assembling California“. Part of his Pulitzer-winning series, “Annals of the Former World,” the book offers a comprehensive and accessible tour through the geological history of California, crafting a fascinating narrative that is as engaging as it is informative.

John McPhee is an acclaimed American writer and pioneer of creative nonfiction, renowned for his deeply researched and beautifully crafted works that often explore topics related to nature, science, and geography. A long-time staff writer for The New Yorker and the author of over 30 books, McPhee is celebrated for his ability to turn seemingly ordinary subjects—such as geology, oranges, or transportation—into compelling narratives. His distinctive style blends meticulous research with accessible, often poetic prose that has been widely immitated. I’ve read several of McPhee’s books and while some of the work can be hard going, I’m usually very satisfied once I’m done. Assembling California is, in my opinion, one of his best.

Here’s an excerpt:

An old VW bus is best off climbing the Sierra from the west. Often likened to a raised trapdoor, the Sierra has a long and planar western slope and—near the state line—a plunging escarpment facing east. The shape of the Sierra is also like an airfoil, or a woodshed, with its long sloping back and its sheer front. The nineteenth-century geologist Clarence King compared it to “a sea-wave”—a crested ocean roller about to break upon Nevada. The image of the trapdoor best serves the tectonics. Hinged somewhere beneath the Great Valley, and sharply faulted on its eastern face, the range began to rise only a very short geologic time ago—perhaps three million years, or four million years—and it is still rising, still active, continually at play with the Richter scale and occasionally driven by great earthquakes (Owens Valley, 1872). In geologic ages just before the uplift, volcanic andesite flows spread themselves over the terrain like butterscotch syrup over ice cream. Successive andesite flows filled in local landscapes and hardened flat upon them. As the trapdoor rises—as this immense crustal block, the Sierra Nevada, tilts upward—the andesite flows tilt with it, and to see them now in the roadcuts of the interstate is to see the angle of the uplift.
John McPhee in Assembling California

The Sierra Nevada, a massive mountain range stretching like a spine nearly the length of California, provides the central geological narrative in “Assembling California”. Known for its stark beauty and dramatic peaks, the Sierras are also a textbook example of the immense forces that shape our planet. (We’ve written and will continue to write about them.) McPhee masterfully explicates how tectonic activity shaped this terrain over millions of years, giving readers a sense of the awe-inspiring age and dynamism of the Earth.

A brief bit about the man: Born in 1931, McPhee studied at Princeton University and Cambridge, and his writing straddles diverse topics from basketball to nuclear energy. His primary strength lies in his ability to seamlessly interweave complex scientific principles with engrossing human stories (there’s always an interesting character and the heart of his work), making the intricate world of science both comprehensible and enjoyable to the lay reader. His skill and prolificacy have earned him numerous accolades, including the Pulitzer Prize.

Assembling California stands out for its illuminating journey through California’s intricate geological history. Traveling with the late geologist Eldridge Moores of the University of California Davis, McPhee unpacks the layered story of California’s geology from its seismic activity to its unique rock formations. There is an excellent excerpt in a 1992 issue of the New Yorker.

Moores was a renowned geologist known for his significant contributions to understanding the geological history and structure of the Earth, particularly in relation to plate tectonics. Born in 1938 in Phoenix, Arizona, he spent the bulk of his career as a professor of geology at Davis, where his research significantly advanced the theory of plate tectonics. He was particularly interested in the geology of his adopted home state, California. Moores also held the position of President of the Geological Society of America in 1996. Apart from his boundless energy, Moores’ real gift was his vision: his ability to “see” geologic history in a pile of rocks. His passionate teaching style and profound knowledge made him a beloved figure in the field of geology. Moores died in a tragic accident in 2018 while on a field trip in Greece, leaving a significant void in the geology world.

Moores explains to McPhee how the Sierra Nevada range didn’t just emerge from the Earth’s crust, as geologists long thought. Instead, the building blocks bubbled up from faraway rifts in the ocean floor called “spreading centers,” then transported thousands of miles on moving plates and piled up onto the North American continent.

Sierra Nevada Mountains and Owens River (Erik Olsen)

The movement of the Earth’s crust along fault lines, as in the well-known San Andreas Fault, is a central theme of the book. By explaining the shifting of tectonic plates, McPhee brings to life the reality of living in California: a landscape that is constantly, if imperceptibly, in motion. His descriptions of earthquakes, both historic and potential future ones, vividly underscore the seismic hazards associated with residing in the state. McPhee’s ability to humanize these impersonal geologic processes is a testament to his storytelling prowess. You will learn a lot about what happens to the California beneath your feet.

However, “Assembling California” is not just a tale of geological forces. McPhee also weaves in fascinating narratives about gold prospectors and vineyard owners, infusing the state’s human history into its ancient geological story. You really can’t tell the story of modern California without delving into the resource-driven economic narratives that are a fundamental part of the state’s history. We try to do a lot of that in this magazine.

For those who want to go beyond McPhee, another fine author is Simon Winchester, whose “Crack at the End of the World” picks up where McPhee left off, both in terms of theme and approach. Winchester, a British author and journalist known for his popular science writing, explores the devastating 1906 San Francisco earthquake. Like McPhee, Winchester expertly merges detailed geological explanations with human stories, providing a compelling account of one of the most significant natural disasters in American history. This is also a very fine book.

The legacy of “Assembling California” lies not just in its rich storytelling but also in the path it blazed for a new kind of popular science writing – one that’s engaging, comprehensive, and profoundly human. By understanding our planet’s past and the forces that shape it, we are better prepared to navigate its future. As readers, we owe a debt of gratitude to writers like McPhee and Winchester who, through their craft, help us appreciate the intricate dance between the Earth’s geological processes and human civilization.

Since McPhee wrote “Assembling California,” technology has made leaps and bounds in the field of geology. Advancements in technology like LIDAR (Light Detection and Ranging), which uses lasers to measure distances and can create high-resolution maps of the Earth’s surface, and improvements in seismograph technology and satellite imaging, have allowed scientists to study geological phenomena in greater detail and with better accuracy.

Geology, like all scientific disciplines, evolves over time as new techniques and technologies become available. This progress often refines our understanding of geological phenomena and can lead to new theories and models. We’re still learning a lot about how our state literally came together, with new research being done all the time that sheds light on our mountains, coasts and valleys.

More recent studies of the San Andreas Fault, for instance, have allowed us to better understand the fault’s behavior, including how frequently significant earthquakes occur and what triggers them. For example a 2022 study from Lamont-Doherty Earth Observatory suggests that the San Andreas Fault moves slowly in a process called “creep,” which was previously thought to release tectonic stress and reduce earthquake risk. However, this new research suggests that this creeping segment might instead be accumulating stress, potentially leading to larger and more destructive earthquakes than previously anticipated.

Not exactly good news, but it’s always better to know what’s happening and to have science that backs it up, and McvPhee was a master at helping us understand he way the world works.

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Why Parkfield, California is the Nation’s Earthquake Capital

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When Big Joe Turner sang “Shake, Rattle and Roll,” he probably wasn’t thinking about a dusty little town in Central California, but in Parkfield, it’s practically the town motto.

Parkfield, California, is a quiet, dusty farming town tucked into the rolling hills of the Cholame Valley, just off Highway 46 (worth the drive if you ever have the chance). A few miles down the road lies an historic intersection, the place where James Dean was killed in a near head on collision crash in his Porsche 550 Spyder on September 30, 1955. The collision ended a blazing young career just as it was taking off and cemented Dean’s image as a tragic icon of American cinema. While tourists still visit the nearby memorial, Parkfield itself is better known to scientists than to star-watchers.

Parkfield is an unremarkable town, with one exception: it lies directly atop the San Andreas Fault and is known as the Earthquake Capital of the World. This is not because there are so many earthquakes there, although there are, but because it has one of the highest densities of seismic technology anywhere. In addition to the larger magnitude 6.0 earthquakes that tend to strike about every 22 years, Parkfield also experiences a steady rhythm of smaller quakes. These minor tremors, often below magnitude 1.0, happen with such regularity, that scientists have compared them to “seismic pulsars” for their consistent, almost clock-like behavior. (And for what it’s worth, Petrolia, California actually has the most earthquakes).

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The San Andreas Fault is one of the best known, and most active faults in the world. In the Parkfield area, the San Andreas Fault is constantly shifting—millimeter by millimeter, day by day. This continuous movement is unique to the region, as the fault remains relatively locked in both the northern section around San Francisco and the southern section near Palmdale. While the fault in these other areas stays immobile, the central part near Parkfield steadily creeps, creating a contrast that puts pressure on the locked sections to the north and south.

Parkfield’s main strip, stretching just a quarter mile, hosts a small collection of buildings, including a one-room elementary school, the USGS-Berkeley earthquake monitoring site, a Cal Fire station, and the Parkfield Cafe and Lodge. Outside the cafe, a row of mismatched mailboxes serves the dozen or so homes scattered along a few dirt roads branching off the main street. Parkfield might be a small, obscure town to most Californians, but to geologists fascinated by the workings of the Earth, it’s the epicenter of seismic research.

Every hillside and valley, grassy nook and riverbed is home to some kind of instrument that measures earthquakes. Over the years, these instruments have become more sophisticated and expensive, making it necessary in many cases to fence them off with the threat of arrest. These instruments monitor, hour by hour, or better, millisecond by millisecond, the stirrings of the earth. To geologists, it is ground zero for seismic measurement.

The town is proud of its reputation. A water tower boasts the tourism slogan: BE HERE WHEN IT HAPPENS (see photo). There is also an iron bridge in the town that has the distinction of standing astride the San Andreas Fault. One one side of the creek that runs beneath the bridge is the North American tectonic plate. On the other is the Pacific tectonic plate. Those two plates are moving south and north respectively at a rate of about 2 inches a year. As we all know, that movement creates immense pressure as the two plates seem otherwise locked in place. That pressure will have to be released at some point. It always has. When that happens, we can expect a potentially devastating earthquake that will rock the state from top to bottom.

The writer Simon Winchester calls the fault an “ever-evolving giant that slumbers lightly under the earth’s surface and stirs, dangerously and often, according to its own whims and its own rules.”

Since 1985, a focused earthquake prediction experiment has been in progress in Parkfield. Known as “The Parkfield Experiment“, the project’s stated purpose is to “better understand the physics of earthquakes — what actually happens on the fault and in the surrounding region before, during and after an earthquake.”

Since the mid-1980s, scientists have deployed an array of advanced monitoring devices, including seismometers, strainmeters, creepmeters, and GPS sensors, to capture detailed data on ground movement and strain accumulation. These instruments are designed to measure subtle changes in the Earth’s crust, helping researchers predict seismic events and understand the processes leading up to an earthquake. By continuously collecting data, the experiment has provided valuable insights into the mechanics of fault movement and the potential for earthquake prediction.

An art installation, known as the Parkfield Interventional EQ Fieldwork (PIEQF), used earthquake waves recorded by the USGS seismic network in California to trigger a hydraulic shake table which was installed in an excavated trench. (USGS)

Experts also once bored a 10,000-foot-deep hole into the ground in Parkfield, into which they placed a large array of sensors to measure the earth’s movements. The goal of the $300 million project, called the San Andreas Fault Observatory at Depth, or SAFOD, was to allow scientists to study how faults work and how earthquakes happen. The drilling stopped in 2007, but Parkfield remains a hot spot for geologic research.

Additionally, the Berkeley Seismological Laboratory operates the High-Resolution Seismic Network (HRSN) in the Parkfield area. This network comprises geophone arrays aimed at monitoring microseismicity along the San Andreas Fault, providing valuable data on the fault’s behavior.

Parkfield remains critical to better understanding seismic dangers in California. The fault zone is poorly understood at depth and so far, the predictability of earthquakes in the near term is pretty limited. But devices like these could help improve prediction, especially if there is a large quake. But that’s the rub, really. We need to experience a large earthquake to get the best data to know how to predict later ones. So it is in California.

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How Theodore Roosevelt’s 1903 trip to California gave birth to modern conservation

Theodore Roosevelt and John Muir in Yosemite. Credit: National Park Service

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Theodore Roosevelt is our hero.

The 26th President of the United States was a soldier, a historian, an amateur scientist, a best-selling writer, an avid outdoorsman and much much more. He has been called the “father of conservation,” because, as president, he authorized the creation of 150 national forests, 18 national monuments, 5 national parks, 4 national game preserves, and 51 federal bird reservations. We think he deserves the moniker.

*President Roosevelt and John Muir at the base of the Grizzly Giant.*
*Credit: Photographer: Joseph Nisbet LeConte; Yosemite NP Archives*

But many people may be unaware that TR has a very important California connection. 121 years ago, in 1903, just two years after becoming our nation’s youngest president at the age of forty-two, following the assassination of President William McKinley, Roosevelt embarked on one of the most important Presidential trips in the history of America.

In 1903, President Theodore Roosevelt embarked on a grand tour of the western United States. At the time, Roosevelt was already known for his passion for the outdoors and his desire to protect the nation’s natural resources. This trip would cement his legacy as a conservationist and lead to the expansion of America’s national parks.

The impact of his trip to California is still being felt today.

The trip, taken by railroad, took Roosevelt across the American continent. The 3,000-mile journey began in April from Washington D.C., and took TR through twenty-five states, and lasted nine weeks. He traveled through the American West and stopped at Yellowstone National Park for a hiking and camping trip with naturalist and essayist John Burroughs. He continued on and ended up touring a large swath of the state of California, including Yosemite, which had been declared a national park in 1890.

Yellowstone National Park (National Park Service)

It was a tenuous time for the American environment. Millions of buffalo had been slaughtered across the plains, often for sport, their carcasses left to rot in the sun. The passenger pigeon, a bird that once filled the skies by the billions, had been exterminated. But America was also in the midst of a nature renaissance, and Roosevelt was one of its pivotal figures. The impact of his trip to California is still felt today.

Millions of buffalo were slaughtered during the western expansion of the United States (Wikipedia)

In California, Teddy Roosevelt’s journey was a mix of official duties and personal exploration, reflecting his dual role as a statesman and an outdoorsman. After arriving in San Francisco, Roosevelt was greeted with great fanfare, delivering speeches to large crowds and meeting with local dignitaries. His visit to the city included a tour of its bustling port, symbolizing the growing importance of California as a gateway to the Pacific. Roosevelt also visited Stanford University, where he spoke about education, progress, and the future of the American West. His time in the urban centers highlighted California’s rapid development and its significance in the nation’s expansion.

However, the most profound part of Roosevelt’s time in California came during his visit to Yosemite National Park. He met with naturalist John Muir on May 15th, 1903. The meeting took place on a train in the dusty town of Raymond, California, the closest station to Yosemite. From there, the men traveled 40 miles (about 8 hours) by stagecoach, which gave them the opportunity to get acquainted. They stopped in Mariposa Grove, where TR saw his first sequoia and had his picture taken driving through the “Tunnel Tree,” which no longer stands.

That first night, President Roosevelt dismissed his aides and the press, which was unusual for him because he was a publicity hound. In the wilds of Yosemite, he and Muir spent three days “roughing it,” camping beneath the stars and enjoying conversation around a campfire. It was during those conversations that Muir made the case for the preservation of forests and other natural resources. Likely, these talks created the impetus for Roosevelt’s support for the 1906 Antiquities Act, arguably one of the most important pieces of conservation law in the United States. With the power to proclaim lands as monuments in the public interest, Roosevelt in 1908 set aside some 800,000 acres as Grand Canyon National Monument. Congress later gave it a national park status.

Arguably, no other President has had such a singular impact on protecting American lands, and it’s fair to say, we think, that his visit to California had a lot to do with it.

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