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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Unraveling the Geology Behind Palos Verdes’ Ongoing Landslide Crisis

A neighborhood threatened by landslides at Portuguese Bend on Palos Verdes (Erik Olsen)

For decades, geologists and engineers have been aware that the Portuguese Bend region of Palos Verdes is prone to landslides. Early maps and aerial surveys from the 1930s show continuous movement from the upper hills towards the high cliffs and bluffs that reach the Pacific Ocean.

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Over the years, with a few exceptions, the ground movement was relatively slow, averaging about a foot per year. However, after the intense rains of the past year or two, the land is now shifting much more rapidly—up to 9 to 12 inches per week—plunging neighborhoods and communities built on this unstable terrain into panic and disarray. This accelerated movement has caused irreparable damage to some homes and led California to declare a state of emergency.

Aerial survey from the 1930s showing landslide potential at Portuguese Bend in Palos Verdes (Ranch Palos Verdes city government)

People have been allowed to build homes at Portuguese Bend largely due to a combination of historical oversight, demand for coastal real estate, and limited understanding of the area’s geologic instability when development first began. In the 1950s and 1960s, when much of the residential development in the area took place, there was less awareness and fewer regulations regarding the risks of building on unstable ground. Additionally, the picturesque coastal views and desirable location made Portuguese Bend an attractive area for developers and homeowners. Despite known landslide risks, building permits were often issued because of insufficient geotechnical assessments, political and economic pressures, and a lack of stringent land-use policies at the time. Over the years, as the understanding of the area’s geologic hazards has grown, there have been more restrictions and efforts to mitigate risks, but many homes already exist on land prone to movement.

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The situation is similar to building homes in fire-prone areas – well-known to Californians, of course – within the so-called Wildland-Urban Interface (WUI), where human development meets and mixes with natural landscapes, creating a high-risk zone for natural disasters.

Small landslide at Portuguese Bend in Palos Verdes (Erik Olsen)

Portuguese Bend is one of the most active landslide zones on the peninsula. Here, the earth moves continuously, almost imperceptibly at times, but the effects are undeniable. The land isn’t just sliding; it’s flowing—like a slow-moving river of rock and dirt—down a natural depression, a sort of bowl or gulch formed by the interplay of tectonic activity and erosion. This gradual yet relentless descent toward the sea is driven by a combination of factors: the underlying geology of ancient marine sediment layers, heavy rainfall, and the constant forces of gravity pulling on the steep slopes. As a result, roads buckle, homes crack, and entire sections of land shift over time.

The geological makeup of Palos Verdes is complex and varied. The most prominent rocks on the Palos Verdes Peninsula, and the most crucial in terms of slope stability, belong to the Miocene Monterey Formation, which we wrote about in a previous article. This formation, over 2,000 feet thick in some areas, has been divided into three distinct members based on their rock types: the Altamira Shale, the Valmonte Diatomite, and the Malaga Mudstone, arranged from oldest to youngest.

Portuguese Bend at Palos Verdes

The Altamira Shale primarily consists of thin-bedded sedimentary rocks formed from layers of clay, interspersed with numerous layers of tuff, or volcanic ash that has largely transformed into weak clays over time. Thick deposits of volcanic ash, laid down millions of years ago, have been compacted into a clay-like material known as bentonite. When bentonite comes into contact with water, it becomes extremely slippery, acting like a natural lubricant. This slippery nature has been a major factor in triggering landslides throughout the Rancho Palos Verdes area, where the land’s stability is continually undermined by these underlying geological conditions.

Another factor contributing to landslides is the region’s tectonic activity. Palos Verdes sits above several active faults, including the Palos Verdes Fault. The movement along these faults exerts stress on the rock formations, leading to fractures and cracks that weaken the slopes. These cracks often become pathways for water to seep into the ground, further destabilizing the already precarious terrain.

The road along the coast at Portuguese Point has been moving for decades, a slow but relentless reminder of the dynamic nature of California’s landscape. (Erik Olsen)

Water plays a crucial role in triggering landslides in this region. Heavy rains, especially those associated with El Niño events like the atmospheric rivers of the last few years, can lead to a rapid increase in groundwater levels. When water infiltrates the ground, it increases the pressure within the soil and rock, reducing the friction that holds everything together. In Palos Verdes, where irrigation, septic systems, and urban development are common, human activities can exacerbate this natural process by altering drainage patterns and increasing water saturation in vulnerable areas. This convergence of natural and human-made factors makes the slopes more prone to sliding, particularly during or after intense rainfall.

To combat this, construction teams have installed a series of dewatering wells and pumps to actively extract groundwater from deep within the hillside. By lowering the water table and reducing the amount of water that saturates the soil, these efforts help to decrease the pressure within the slope and mitigate the risk of further ground movement. This method of dewatering is a crucial element in stabilizing the land, as it helps prevent the soil from becoming too heavy and reduces the lubricating effect that water has on the bentonite clay layers.

Closed road at Portuguese Bend in Palos Verdes (Erik Olsen)

Coastal erosion is another critical factor. The rugged cliffs of Palos Verdes are constantly being eroded by the ocean’s waves, wind, and rain. Over time, wave action undercuts the base of the cliffs, removing the support for the upper layers and leaving them hanging precariously over the ocean. As the base erodes away, the upper cliffs become more susceptible to collapse. When combined with the weakened geology and increased groundwater levels, this coastal erosion sets the stage for dramatic landslides.

Portuguese Point cliffs are part of the constant coastal erosion process at Palos Verdes aerial photo (Erik Olsen)

Recent studies are shedding new light on why landslides in Palos Verdes continue to be a concern. Geologists are now using advanced technologies, such as ground-penetrating radar and satellite imagery, to better understand the underground conditions that contribute to landslides. A study from the University of California, Los Angeles, has explored how even minor shifts in groundwater levels, exacerbated by climate change and increasingly unpredictable weather patterns, can tip the balance and trigger significant slope failures. This research emphasizes that it’s not just the obvious heavy rainfall events that pose a threat; subtle changes in water content due to human irrigation, drought, or even slight variations in precipitation can also destabilize these slopes over time.

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Moreover, new geological mapping and subsurface studies have provided a clearer picture of the fault lines and the fractured rock layers beneath Palos Verdes. These studies suggest that the interaction between multiple fault zones may be more significant than previously thought, potentially increasing the region’s susceptibility to movement. Understanding these interactions is crucial for predicting future landslides and developing mitigation strategies.

But in the end, nature will likely have the final say.

Portuguese Bend in Palos Verdes (Erik Olsen)

The picture that emerges from these studies is one of a region where natural geological processes and human activities are in a delicate balance. It’s an ongoing fight that really offers a precarious vision of the future for residents and others who use the area for recreation. The weak rock formations, intersecting fault lines, and relentless coastal erosion create an environment where the land is always moving and on the brink of collapse. Add to this the unpredictable impacts of climate change, which can bring more intense storms and alter precipitation patterns, and it becomes clear why Palos Verdes is so prone to landslides.

Efforts to mitigate the risk are ongoing. Local governments and geologists are working to develop more effective monitoring systems and better land-use planning guidelines to manage development in these sensitive areas. Understanding the complex geology and hydrology of Palos Verdes is critical to preventing future disasters and protecting the communities that call this beautiful but unstable coastline home.

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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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California’s Monterey Formation: Unraveling the Secrets of a Fossil-Rich, Oil-Bearing Geological Wonder

Monterey Formation rocks near Newport Beach (Erik Olsen)

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California’s Monterey Formation is one of the most fascinating geological formations in the United States. Stretching along the California coast from San Francisco to Los Angeles, this formation is notable for its incredible diversity of siliceous rocks—rocks rich in silica, such as shale, chert, diatomite, and porcelanite. While these rocks are interesting to geologists, the Monterey Formation is also significant for its potential to explain the origins of petroleum deposits that have fueled California’s economy for over a century. NASA’s Jet Propulsion Laboratory once called it “California’s primary petroleum source rock.”

Fracture network of joints and cross-joints exposed on bedding surface of siliceous shale. Note linked, larger-aperture fracture in center with oxidation rim. Montaña de Oro State Park. (NASA JPL)

At the heart of the Monterey Formation’s geology is the unique composition of many different types of rock that come together in such a way that they create an ideal environment for trapping oil. The intricate layering of organic-rich shales, siliceous rocks, carbonates, and diatomites forms a complex network of porous and permeable spaces, allowing oil to migrate into these reservoirs. Over time, these rocks act like natural sponges, effectively capturing and holding large quantities of oil within their formations, making the Monterey Formation one of California’s most significant petroleum sources. It is estimated that over 38 billion barrels of oil have been produced to date from fields whose source rock is the Monterey.

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Diatomite, a light, porous rock formed from the fossilized remains of diatoms, is a dominant feature. Diatoms, microscopic algae with silica-based cell walls, thrived in nutrient-rich waters, leading to the thick layers of sediments that later became diatomite. Chert, another key rock type in the formation, is formed from the recrystallization of biogenic silica, adding to the complexity of the geological record. Interspersed with these are organic-rich shales, which contain substantial amounts of organic material called kerogen. Over millions of years, kerogen undergoes a biological transformation becoming the oil and gas that now serve as the backbone of California’s petroleum industry (see our story on the history of the Long Beach oil industry).

The Monterey Formation displays a fascinating and unusual mixture of geological deposits, from deep ocean basins to shallow continental shelves. During the Miocene, upwelling currents along the California coast brought nutrient-rich waters to the surface, fostering high biological productivity and depositing vast amounts of biogenic silica, a form of silicon dioxide (SiO₂) that is produced by living organisms. Periods of fluctuating sea levels, driven by climate changes and tectonic shifts, further shaped the environment. During low sea levels, parts of the continental shelf were exposed, allowing for erosion from wind and sun. These would shift to periods of high sea levels, which allowed for denser, deep-water sedimentation. In some layers, the presence of evaporites—minerals that form from the evaporation of water—suggests extensive episodes of arid conditions, similar to what we are experiencing now with California’s recurring periods of drought.

Offshore oil platforms along California’s coast drill into the Monterey Formation, either tapping directly into its fractured shale or extracting oil that has migrated into more porous sandstone reservoirs. (Photo: Erik Olsen)

Much of the pioneering research on the geology, formation, and unique composition of the Monterey Formation was conducted by the late Robert Garrison, a distinguished professor of oceanography at the University of California, Santa Cruz. Garrison was considered the foremost expert on the Monterey Foundation, and his work was instrumental in revealing how the Monterey Formation’s diatomaceous and phosphatic deposits were shaped by a combination of oceanographic upwelling, climatic shifts, and tectonic activity during the Miocene epoch.

Petroleum geologists find the Monterey Formation especially intriguing because it serves as both a source and a reservoir for oil and gas, allowing them to better understand the processes of oil and gas generation, migration, and accumulation, as well as to develop more efficient extraction methods to maximize its economic potential. They are also quite beautiful. Walk along the beach near Crystal Cove in Orange County, for example, and examples of Monterey Formation rocks abound.

Monterey Formation rocks near Little Corona in Newport Beach (Erik Olsen)

Oil is formed from the remains of ancient marine organisms, such as plankton and algae, that were buried under layers of sediment and subjected to heat and pressure over millions of years, transforming them into hydrocarbons. Some of these hydrocarbons migrated into more permeable rocks, creating substantial oil fields that have been exploited for decades in Southern California. Certain layers of the Monterey Formation, particularly the fractured chert and dolomitic sections, also serve as excellent reservoirs due to their porosity and permeability, allowing them to store oil and gas for long periods of time.

Beyond its geological and economic importance, the Monterey Formation is a treasure trove for paleontologists. Its layers preserve a variety of marine fossils, including diatoms, radiolarians, foraminifera, and coccolithophores. These microfossils offer a detailed look at past ocean conditions, helping scientists reconstruct the climatic and oceanographic history of the Miocene epoch. Additionally, the formation contains fossils of larger marine vertebrates, such as whales, seals, and fish, providing further insight into the ecosystems of ancient oceans.

Microscope image of microfossils and organic matter in Monterey rocks. (Cal State Long Beach)

However, the Monterey Formation is not just a source of knowledge and resources; it also presents challenges, particularly in terms of potential environmental harm and geohazards like landslides. The soft, diatomaceous earth layers within the formation are prone to landslides, especially when water-saturated or fractured by tectonic action. This makes some coastal areas of California, where the Monterey Formation is exposed, particularly vulnerable to slope instability, posing risks for construction and development. Many recent news stories have documented the increasing rate at which the California coast is tumbling into the sea. An excellent recent book on the subject is Rosanna Xia’s California Against the Sea: Visions for Our Vanishing Coastline.

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California’s geology is a remarkable mosaic that tells a story of immense geological diversity and dynamic processes. Among its many treasures, the Monterey Formation stands out as a geological marvel—its intricate layers, rich fossil beds, and significant economic potential continue to captivate scientists and researchers from around the world. This unique formation is more than just rock; it is a time capsule that preserves millions of years of Earth’s history, from ancient marine ecosystems to dramatic shifts in climate and tectonic activity. As geologists, paleontologists, and environmental scientists delve deeper into its mysteries, the Monterey Formation reveals invaluable clues about the past while shaping our understanding of California’s ever-evolving landscape. It serves as a profound reminder of the powerful forces that have sculpted one of the most geologically varied regions on the planet and continues to inspire exploration and discovery in the fields of Earth science.

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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The Pacific Coast Highway (PCH): Icon of American Scenic Roadways

Pacific Coast Highway near Big Sur (Erik Olsen)

The Pacific Coast Highway (PCH), also known as California State Route 1, is one of the most iconic roads in the United States, renowned for its breathtaking views of the Pacific Ocean and rugged coastline. This scenic highway stretches over 650 miles from Dana Point in Orange County in Southern California to Mendocino County in Northern California, offering travelers unparalleled vistas and a quintessential Californian road trip experience. While some suggest that PCH runs from Mexico to Canada, that is mistaken. U.S. Route 101 continues north from California, running along the coast through Oregon and Washington, up to the Olympic Peninsula. That said, it is still the longest state route in California and the second-longest in the US after Montana Highway 200. The story of its construction is as dramatic and intricate as the landscape it traverses.

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The origins of the Pacific Coast Highway date back to the early 20th century, when the automobile was becoming an essential part of American life. The idea for a coastal highway was initially conceived to connect the state’s isolated coastal communities and improve access to California’s scenic beauty. The concept gained traction in the 1910s and 1920s, and construction began in earnest in the 1930s, to provide jobs during the Great Depression.

Lovely aerial of Pacific Coast Highway in Central California

“It took decades to get the highway built,” Carina Monica Montoya told the Los Angeles Times. Montoya is the author of, “Pacific Coast Highway In Los Angeles County” (The History Press, 2014).

The construction of the PCH was an engineering marvel, given the challenging terrain it had to navigate. The road had to be carved out of steep cliffs, cross numerous rivers, and be supported by bridges spanning deep ravines. One of the most significant and iconic portions of the highway, the Big Sur section, presented formidable challenges. This stretch of the road, which runs between San Simeon and Carmel, required extensive blasting and drilling into the rugged coastal mountains. The effort was spearheaded by the California Division of Highways (now CalTrans), with a workforce comprising both state employees and workers from the Civilian Conservation Corps (CCC), a New Deal program.

Key figures in the design and construction of the PCH included engineers and architects who had to innovate continuously to address the formidable natural obstacles. One notable engineer was John D. Isaacs, a prominent builder who contributed to the design and construction of several key bridges along the PCH, including the famous Bixby Creek Bridge. His innovative approach to bridge engineering helped overcome the difficulties presented by the steep canyons and coastal bluffs.

The Pacific Coast Highway took decades to complete fully, with different sections being opened to the public at various times. The Big Sur segment, for example, was officially completed in 1937 after nearly 18 years of labor. The total cost of constructing the highway is difficult to pinpoint precisely, given its piecemeal development, but it ran into tens of millions of dollars—an immense sum at the time.

The Pacific Coast Highway near Santa Monica, California, circa 1930s.

Several colorful characters also play a role in the highway’s history. The Pacific Coast Highway might not exist today if May Rindge, a resolute landowner, had succeeded in her long battle against the county. Since at least the 1890s, a primitive road, often submerged at high tide, hugged the rocky coast between Santa Monica and Malibu, passing under a natural arch and ending at a locked gate on Rindge’s 17,000-acre ranch.

As the owner of Rancho Topanga Malibu Sequit, Rindge was determined to protect her property. She and her late husband had long fought to keep homesteaders off their land. In 1906, she even forced the Southern Pacific Railroad to divert its Santa Barbara line around Malibu and through the San Fernando Valley.

In 1907, when the county proposed extending the coastal road through Malibu, Rindge posted armed guards at the entrances to her ranch and contested the county’s power of eminent domain in court. A stalemate ensued for years, but the road’s prospects improved in the early 1920s when it was included in the planned Roosevelt Highway. In 1923, the U.S. Supreme Court upheld the county’s right to appropriate the land for the highway, and in 1925, a superior court judge granted the county title to the right-of-way in exchange for $107,289, finally ending the dispute.

The book “The King and Queen of Malibu: The True Story of the Battle for Paradise” by David K. Randall (2016) tells the story of Ringe and a wonderful history of Malibu.

Today, the Pacific Coast Highway is one of the most famous and iconic strips of road in the world. Featured in countless commercials as well as movies and TV shoots, sections of PCH are immediately recognizable. Of course, it helps a lot that the highway in in such close proximity to legions of DPs (Directors of Photography) who live in Los Angeles and work in commercials and film. Shooting on the highway is an easy day trip from LA and Hollywood, although it can be difficult to get permits to film on the highway given it is such a busy working road.

That said, the highway faces significant challenges due to climate change and coastal erosion. Rising sea levels and increased storm activity are accelerating the natural erosion processes along California’s coast. This has led to frequent landslides and road closures, particularly in the Big Sur region. One notable event was the massive landslide in 2017 at Mud Creek, which buried a section of the highway under 40 feet of debris, closing it for over a year and requiring extensive repairs. A timelapse of the landslide produced by the United States Geological Service can be seen here.

The Pacific Coast Highway in Newport Beach (Erik Olsen)

The New Yorker ran a piece on the concerns about the highway’s future viability as a means to travel long distances along the coast.

The Washington Post wrote back in 2021, “the engineering folly of a road built on sheer cliffs has meant that closures are annual events — the “whens,” not “ifs” — for the people and the economy it supports.”

The most recent slide to afflict the region took place in April 2024 following heavy rains, when large chunks of the road broke off, tumbling down a cliff and into the ocean near Rock Creek Bridge. Safety officials closed off about 40 miles of road as crews worked to assess the damage and stabilize the road.

Rosanna Xia, a reporter for the Los Angeles Times, masterfully chronicles the problems facing PCH and the California coast in general due to climate change and erosion in her book California Against the Sea: Visions for Our Vanishing Coastline.

Although the Pacific Coast Highway remains one of the greatest road trip routes of all time, the challenges in maintaining its full length are significant for the state and its residents. Despite its enduring popularity, the highway often operates in sections due to frequent closures and repairs caused by natural disasters like landslides, erosion, and wildfires. These ongoing issues demand substantial resources and effort to keep the entire highway operational, making its full-length service a constant struggle.

Still, it remains a pretty excellent place to take a drive. As the Boss once put it, roll down the window and let the wind blow back your hair.

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Black Gold Beach or How Oil Transformed Long Beach and Built the Southern California Economy

Signal Hill oil development (Photo: The Huntington Library, Art Museum, and Botanical Gardens)

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Southern California is best known for its sun-soaked beaches and Hollywood glamour, but it also has a wilder, largely forgotten past: it was once an oil kingdom. It’s a story even many Californians don’t know, a tale of spectacular gushers, fortunes won and lost, and larger-than-life characters straight out of a movie. Without oil, Los Angeles, and much of Southern California, would be very different places today.

The story of oil in Southern California is inextricably linked to the Long Beach fields, an area that once seemed more like a scene from Texas or There Will Be Blood than the Golden State. The discovery of oil in this region wasn’t just a footnote in economic journals; it was a seismic event that transformed the landscape, both literally and metaphorically. And it provided an industrial center of gravity to a region of the state that was just beginning to emerge as one of the world’s great gateways of commerce.

The early 20th century was the beginning of the era of oil in California. On June 23, 1921 at 9:30 a.m., the Alamitos No. 1 oil well on Signal Hill in Long Beach was drilling 2,765 feet beneath the surface when the drill struck an underground oil deposit. This oil was under high pressure due to natural gas, blowing a gusher of oil over 100 feet high, and heralding the start of the Long Beach oil boom.

This event marked the discovery of one of the most prolific oil fields in the Los Angeles basin. Throughout the 1920s, Signal Hill, along with the nearby Santa Fe Springs field, experienced numerous blowouts, which erupted into dramatic pillars of flame that could be seen for miles. These incidents eventually prompted calls for stricter safety regulations. Consequently, in 1929, the state mandated the use of blow-out prevention equipment on all oil wells drilled in California.

Signal Hill quickly mushroomed into a forest of oil derricks, with fortunes being made overnight. As one of the most productive oil fields in the world, the Long Beach field was at one point yielding a staggering one-third of California’s total oil production. By the mid-1920s, California was producing nearly a quarter of the world’s entire petroleum supply, much of it from the Long Beach area.

Signal Hill, Long Beach oil development. (Public domain)

That so much oil is present beneath the surface of this stretch of Southern California is a gift of geology. Millions of years ago, the area that is now Long Beach was covered by the ocean. This marine environment was ideal for the accumulation of organic material, such as the remains of tiny plants and animals, on the ocean floor.

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Over time, layers of sediment buried this organic matter. The high pressure and temperatures associated with deep burial initiated the transformation of this organic material into hydrocarbons – essentially, the formation of oil. Southern California is, of course, known for its active tectonics, influenced by the Pacific and North American Plate boundary. This tectonic activity has created a complex network of faults and folds in the earth’s crust in the Long Beach area.

The folding of the earth’s layers into anticlines (a type of fold that is convex up and has its oldest beds at its core) and the formation of fault traps (where displaced rocks create a seal that traps oil) are particularly important. These structures create reservoirs where oil can accumulate and be preserved over geological time scales.

As the oil flowed, so did the stories of those who sought their fortune in black gold. Perhaps the most famous of these was Edward L. Doheny, a name synonymous with California oil. Doheny, an ambitious prospector, was one of the first to recognize the potential of the Los Angeles Basin’s oil fields. His success in the oil industry was meteoric, but it was not without controversy, as he was later embroiled in the infamous Teapot Dome scandal.

Portrait of oil magnate Edward L. Doheny (Wikipedia)

The impact of oil production in Southern California extended beyond economics. It reshaped the region’s landscape, both physically and culturally. Towns sprung up around oil fields, and workers flocked to the area, drawn by the promise of jobs and prosperity. Long Beach, once a sleepy coastal town, burgeoned into a bustling city.

During the 1920s, regulations on well spacing were minimal, allowing Signal Hill to market narrow town lots. These lots were swiftly purchased by aspiring oil tycoons who installed wells so close to each other that they almost touched. Despite the dense placement, the wells generally remained profitable, though they rapidly depleted the oil field. The hill earned the nickname “Porcupine Hill” due to its appearance from afar, bristling with numerous wooden oil derricks since the more compact “nodding-donkey” pumpjack had not yet been developed.

The booming oil industry in the region attracted a massive influx of workers and investments. As oil fields expanded, Long Beach rapidly transformed from a seaside resort into an industrial powerhouse. The surge in economic activity and the availability of abundant oil fueled the growth of industries in and around Long Beach, including the burgeoning shipping and maritime sectors.

Container ships outside the Port of Los Angeles during the Covid lockdown in 2020. (Photo: Erik Olsen)

The construction of the Port of Los Angeles, which began in earnest in the early 1900s, was driven by the need to support the growing economic activities in Southern California, including agriculture, manufacturing, and oil. The proximity of Long Beach to the port, only about 20 miles south, meant that it was strategically positioned to benefit from and contribute to the port’s activities. The port served as a critical node for shipping oil, among other goods, which further integrated Long Beach, and Southern California as a whole, into the global trade system.

Signal Hill in Long Beach today. (Erik Olsen)

Moreover, the infrastructure developments necessary to support the oil industry, such as roads, railroads, and later pipelines, also facilitated the growth of the port. These developments enhanced the logistical capabilities of the region, making it more attractive for commercial and industrial activities. The oil boom thus not only transformed Long Beach but also had a cascading effect on the development of the Port of Los Angeles, cementing the region’s role as a vital hub in international trade and commerce.

As big and diverse in industry Los Angeles has become, it mostly started with oil. The fact that Los Angeles is now hardly known for oil, but better known for its massive entertainment and tourism economies is an astonishing transformation.

Of course, the influx of wealth and people also brought challenges, including environmental concerns and the need for regulatory oversight. It is well known that several major oil spills have taken place off the coast, ruining beaches and killing animals by the millions. In 1969, the Santa Barbara oil spill released vast quantities of oil into the ocean, creating an environmental disaster along the California coastline. This catastrophic event galvanized public awareness and activism, leading to the creation of the first Earth Day, as well as significant environmental legislation, including the establishment of the U.S. Environmental Protection Agency.

The oil slick visible around Platform A in the Santa Barbara Channel emanated from fissures in the seabed. (Photo: USGS)

Oil spills continue to take place in Southern California and the existence of 26 rigs off the coast are a reminder of that oil boom era. Those rigs are coming to the end of their productive life, however, and an on-gong controversy is what to do with them. Remove them or leave them — or part of them — as artificial reefs?

Over time, oil production in Southern California has waxed and waned. The easily accessible oil has largely been extracted, and production has declined from its mid-20th-century peak. Yet, the legacy of this era persists. It’s etched into the region’s physical and cultural landscape, from the bobbing oil derricks still dotting Signal Hill to the fortunes and institutions built on oil money.

The story of oil in Southern California, particularly the Long Beach fields, is a saga of geologic luck, ambition, ingenuity, and, at times, dangerous greed. It’s a chapter in the state’s history that’s as rich and complex as the oil that still lies beneath its surface, and yet it remains largely unknown to many people who think of Southern California as a paradise of sand and rolling waves.

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