Driving Through the Most Dangerous Plate Boundary in the World: The Sea Floor that Became the Greatest Agricultural Region on Earth

Welcome to one of the strangest places on the planet! It's the size of West Virginia, but flatter than the Mississippi River Valley. It was once America's Serengeti, but 95% of the original landscape has been altered. It originated as the bottom of a sea, but now grows most of the nation's produce, and practically all of the nation's walnuts, almonds, and pistachios. It has been a major oil and natural gas producer. It is the Great Valley of California.

The Great Valley originated as a forearc basin, the seaway that is sometimes present between an oceanic trench/subduction zone and the margin of the continent. Tens of thousands of feet of sediment were deposited between the Jurassic Period and the mid-Cenozoic. As noted in the last post, the sediments have yielded up a fascinating collection of fossils over the years, including mosasaurs, plesiosaurs, ichthyosaurs, and even the fragmentary remains of a few dinosaurs. The valley was a seaway for the better part of 200 million years.

It is no longer a seaway. In the last few million years, California's tectonic framework underwent huge changes. The subduction zone was extinguished in the central and southern parts (subduction continues in the north state). A new plate boundary emerged: the San Andreas transform fault. Compressional forces along bends in the fault line raised the Coast Ranges, and the seaway of the Great Valley slowly gave way to river deltas, and then alluvial fans. In the last five million years, the Great Valley has been a terrestrial environment, with numerous river channels, gigantic lakes and vast grasslands. Large herds of grazing animals wandered the plains, pursued at times by terrifying predators (look for them in the next post of the series). Countless millions of birds made use of the wetlands during their long seasonal migrations.

The biggest and most far-ranging change in the Great Valley during the last five million years may have been that which took place only in the last 150: agricultural development. Millions of acres of grasslands, lakes and wetlands were drained and plowed. The rivers were dammed and diverted into artificial watercourses that took them hundreds of miles from their natural channels. Thousands of wells were drilled that brought prehistoric groundwater to the surface. Parts of the valley subsided thirty feet or more as the water was withdrawn. A mere 5% of the valley floor retains its natural character. Most of the animals are gone, shot to extinction (the California Grizzly Bear, for instance), or pushed to marginal environments in the Sierra Nevada or the Coast Ranges. The migratory birds are crowded into a few precious wildlife refuges up and down the valley.

I'm not really writing this to criticize the agricultural development of the valley. We have billions of people on the planet, and they insist on eating, so it would be foolish not to utilize some of the richest soils on the planet. I would even suggest to people who don't live in the valley that they might have a bit more respect for the people who work hard for low wages to plant and harvest the food that you eat. On the other hand, we do a lot of things wrong in our approach to agricultural development, and the waste of water is one of those things. The ongoing four-year drought has exacerbated the problem. There are problems with the overuse of pesticides and antibiotics, and with agricultural waste disposal. In many ways we are fouling (and paving over) our nest.

Still, living here does have some benefits. Given our journey through the most dangerous plate boundary on the planet, the Great Valley doesn't exactly look geologically menacing. It is relatively far away from the most active earthquake faults of the state, and is even farther away from the most dangerous of the state's volcanoes. We don't get hurricanes, violent thunderstorms or blizzards, and tornadoes are exceedingly rare. The idea of dangers from landslides is laughable (except that I know of at least one fatality in Modesto caused by a slide). But we do have two threats: droughts and flooding.We are in the midst of the worst drought in recorded history, but with the development of an El Nino weather pattern in the Pacific, we could have catastrophic floods in only a few months. We can never really predict what can happen. In 1861-62 the floods were widespread that the state capitol had to be removed to San Francisco for a few months. The valley was a gigantic lake twenty miles wide in places.

Flooding on the San Joaquin River in 2006.

The map below shows what could happen if we get a repeat of the 1861-62 floods, an event the meteorologists call an atmospheric river storm (ARKStorm). They also refer to this as the "other big one", because the potential for damage is greater than that of a major earthquake, at least in the Great Valley.

In the Great Valley, geology conspired to transform a sea floor into the richest agricultural region on the planet. For all the flat lands, it is an interesting place to study. In the next post we'll take a look at the strange things we've found just beneath the surface. In a garbage dump of all places.

A Truly Great Valley: Ruminations on California's Most Valuable Resource

What is the most valuable mineral commodity in California, the so-called Golden State? Gold? Not hardly. We produced somewhere around 150 million ounces of the stuff over the last 160 years, netting riches for a few, and producing a sad heritage of scarred hillsides, fouled rivers and bays, and thousands of people (and their cultures) dead before their time.

So what is it? California has one of the largest ore bodies in the world of borate minerals, and we produce something like 50% of the world's supply of these important industrial chemicals. But their value pales in comparison to the most precious resource.

What about rare-earth elements?  For several decades California was the world's largest producer of these technologically important chemicals before being supplanted by China, which now produces around 95% of the world supply. Nope, it's not that one either.

There's oil, of course. We've been drilling it for more than a century, and currently produce around 200 million barrels a year. At current prices, maybe $15 billion a year. But that's not our most productive resource either.

No, our most valuable mineral resource is dirt. Or more specifically, soil. Our Great Valley is covered with it, and we produce incredible riches by converting the macronutrients stored on the surface of clay particles into carbohydrates, which are then consumed in large amounts by populations worldwide. In other words, we produce food. Lots and lots of food, more than 200 different kinds. For a variety of geological reasons, the soils in the Great Valley are among the richest, most productive on the planet. Our valley, comprising about 1% of the agricultural lands of the United States (about 15,000 sq. miles out of 1,500,000 sq. miles) produces about 25% of the country's table food.

I imagine that my description sounds a bit like a public relations campaign, but it's not. I was thinking about the valley, my home, as I traveled through the northern half of it on Thanksgiving weekend. For more than 200 miles, I passed one planted field after another pretty much without a break, other than a few widely spaced farm towns (Sacramento and Stockton being two huge urban exceptions). In that entire distance I could see but a view spots where the valley resembled anything like its natural condition, including the Sacramento National Wildlife Refuge near Willows, and a  handful of river crossings. We have, I realized, treated our most valuable mineral resource the same way we dealt with gold when it was discovered: get as much out of it as possible, and damn any repercussions. We've tried to squeeze every last bit of profit from the rich soil, through the addition of fertilizers, pesticides, herbicides and imported water until the natural ecosystem was in a shambles. Our valley is one of the most altered landscapes on the planet. The gold miners affected a few tens or hundreds of square miles with poisons and wastes. In the Great Valley we've affected around 15,000 square miles.

Of course, it couldn't be any other way. We have to eat, and the story of humans for the last 8,000 years or so is the development of agriculture leading to the development of cities and civilizations. We could not colonize a landscape like California without providing a source of food, shelter and water. The wistfulness in my thinking the other day is the fact that we did this thing with no planning, and no thought to sustainable development. The bounty of the valley was also sustaining millions of birds, grazing animals, amphibians, and fish, and we simply plowed over those habitats and many of the animals simply disappeared. It's only in the last few decades that we've started to recognize that we are truly part of a worldwide ecosystem, and that there is value in maintaining ecological diversity. We are finally setting aside some of the leftovers of our headlong development of the valley in an effort to provide for the millions of birds, fish and other animals that have depended on the valley for hundreds of thousands of years.

The Great Valley is a gigantic geological anomaly in the normally mountainous American west. It's incredibly flat, flatter maybe even than Florida or Louisiana. 400 miles long and around 30-40 miles wide, it is a vast trough that has been collecting sediments for around 140 million years, first as a seaway formed between a subduction zone and the coastline (a forearc basin), and later as a series of river floodplains and deltas. In places like Bakersfield, the thickness of the sediments approaches 10 miles. In my neck of the woods, they reach half that, a mere 25,000 feet or so (sort of an upside down Mt. Everest).

The "primeval" valley was mostly a dry savanna or short-grass prairie, more desert-like in the south, more oak woodland in the north. Dozens of rivers flowed out of the Sierra Nevada, providing hundreds of miles of riparian habitat. The rivers at the south end of the valley ended in huge ephemeral lakes, the now dry Buena Vista and Tulare lakes. Until 11,000 or 12,000 years ago, the valley teemed with horses, camels, antelope, bison, mammoths, mastodons, sloths, bears, sabertooth cats, lions, and dire wolves. After the great extinction at the end of the last ice age, the valley still had vast herds of pronghorn antelope, deer, and tule elk who were hunted by wolves, coyotes, grizzly bears, and mountain lions, and the new arrivals, the humans.

For birds, the valley was paradise. Sure, when the weather got hot billions of them migrated far to the Arctic north where they could consume the trillions of bugs and breed, but when the winter came, they migrated back to the snow-free Great Valley and fed on the marsh grasses, berries, fish, amphibians and bugs that lived along the rivers, marshes, lakes and other wetlands in the verdant valley.

So it was that I was visiting one of the few spots in the valley where one could imagine the way things once were before the agricultural revolution. The Sacramento National Wildlife Refuge is one of a series of reclaimed farmlands and marshes that serve as a winter home of hundreds of thousands of geese, ducks, cranes, and other migratory fowl, as well as the yearlong resident birds and other animals. It is, in fact, a highly regulated landscape, with square plots that are flooded some years, dry in others, managed in such a way as to provide as much forage for the birds as possible. But it recalls the primeval environment. Driving along the auto loop, we were quietly amazed at the sheer numbers of birds. There were thousands of Snow Geese, and at one point literally all of them took flight. The rush of thousands of flapping wings was like the sound of a jet plane.

A lot of us kind of take the Great Valley for granted. It's actually not the nicest place in the world to live, with foul air, dust and heat in the summer, cold tule fogs in the winter, high unemployment rates, and crushing poverty in many areas. But it is we who feed the rest of the state, and much of the rest of the country. We've made a kind of devil's bargain with the land, wresting as much nutrition as we can from the soil, and leaving a bit of the leftovers for the others who inhabit the planet with us. But if you can, give our valley a look, especially on a clear winter's day. I suggest a stop at a place like the Sacramento National Wildlife Refuge just off Interstate 5 near Willows, or the Merced National Wildlife Refuge near Merced and Los Banos. You will be truly astounded to realize that we have our own small version of the Serengeti right here in the middle of the tilled fields.

Birds of My Neighborhood: Geotripper Finds a Moment of Incredible Majesty Amid Environmental Devastation

A White-faced Ibis (Plegadis chihi) at the Merced National Wildlife Refuge

I wonder if you've noticed an additional aspect to my blogging in recent weeks. It wasn't a New Year's resolution because it started well before Christmas, but I realized that I needed to get rid of a few pounds, so I started walking once or twice a day. When a new and more powerful camera landed in my hands, I realized I could get some decent pictures of the numerous birds species I've been encountering during my explorations along the cow pastures and canal levees that are prevalent in my neighborhood.

A Black Phoebe (Sayornis nigricans) at the Merced National Wildlife Refuge

So I've started blogging bird pictures on occasion, such as here, here, and here (click on the words for the link). Is there a geological link in observing birds? I've decided there is, especially in California's Great Valley. The science of the Earth is eclectic, drawing on many different disciplines, including chemistry, physics, astronomy, oceanography, meteorology, and on occasion, biology (think especially of paleontology). Sometimes there is a direct connection, such as when overgrazing or removal of beavers changes the pattern of stream erosion. And land-use issues are one of those areas where geologists can provide an important perspective.

Artificially flooded ancestral wetlands at the Merced National Wildlife Refuge. These are reclaimed farmlands.

One of the most important land-use issues in the Great Valley involves agricultural and urban development and the conflict it causes with the natural habitat that existed prior to the arrival of European settlers. Some 95% of the valley has been plowed over, and all the major (and most of the minor) rivers have been dammed, diverted, or otherwise changed in the service of agriculture. In more recent years, urban growth has paved over prime agricultural acreage, creating a conflict within a conflict. The ramifications of these conflicts extend far beyond the Great Valley. They reach from the northernmost Arctic wastes to the equator, and into South America. The Great Valley, as it turns out, is one of the most critical stops on the migratory flyway for myriads of bird species. Our choices in the valley determine the health of ecosystems thousands of miles away. And most of the wetlands that made the valley such an important flyway stop were drained and plowed decades ago.

Black-necked Stilt (Himantopus mexicanus) at the Merced National Wildlife Refuge

That is why I am kind of thrilled to be writing today about the bird species of my home turf. I have driven by a couple of wildlife refuges for two decades without stopping (what can I say? I live next to the Sierra Nevada and the California Coast; they are a huge distraction). In the last few months, we've been stopping and having a look, and yesterday at the Merced National Wildlife Refuge I saw an incredible thing.

Great Egret (Ardea alba) at the Merced National Wildlife Refuge

The first thing to realize is that the destruction of wetlands has been recognized for many decades, and for years some visionaries have worked to establish protected wetlands. In some cases they have reclaimed former agricultural acreage in a concerted effort to reconstruct some of the original environment that once characterized the valley. There is now a mosaic of wildlife refuges surrounding my community, lined up like islands in a sea of farms and ranches reaching from one end of the valley to the other (a 400 mile stretch). We can never fully recover what was, and will never see the spectacle of millions upon millions of birds descending on the valley floor, but we can see the tens of thousands of the survivors.

Sandhill Cranes (Grus canadensis) at the Merced Refuge

That's what I saw yesterday. I'm admitting my own stupid ignorance here, but I had no idea that we had an American version of the Serengeti Plains a short way from my house. We've probably all seen television documentaries and footage of vast flocks of birds flying and flocking, but I'd never seen such a thing for myself. We headed out to the Merced National Wildlife Refuge because we'd heard they had flooded the wetlands, and that some Sandhill Cranes might be seen. We saw some cranes, but that's not what I found stunning. It was the Ross's (or maybe Snow) Geese.

Ross's Geese (Chen rossii) and Coots at the Merced Refuge

The Ross's Geese spend their summers in the far northern islands of Canada, and spend their winters in California. As we drove the loop road through the refuge, we could see vast flocks off in the distance, and from more than a mile away we could hear their noise. As we drew closer, we could see that there were thousands of them, maybe tens of thousands (some sources mention 60,000 geese). They were chattering and honking, and it was almost deafening. Then the extraordinary thing happened. There was a hush that made us look up, and then a sound like a jet engine began to roar. The ground actually seemed to tremble. Every single one of the ten thousand or so geese was taking flight at once. In less than 20 seconds they were all airborne. I have no idea what set them off, but it was like nothing I've ever seen in my life.

Ross's Geese taking flight

I got a good video of the event, but the compression process during uploading removes the high definition and makes it hard to easily visualize what was happening. I can only say to try and imagine what this piddly movie is showing, and then someday give yourself the opportunity to visit the wildlife refuge during the winter and see it happening for yourself. It's free!

Try something new each day. Your life will be richer for it!

A Different Kind of Snow...

There was supposed to be a snowstorm in San Francisco last night, the first in a very long time, and snow levels in our valley were supposed to reach as low as 100 feet or so, so we set out to see if any had fallen in the Sierra Nevada foothills above our home. If there was any, it melted early, but we found a different kind of snow on the almond orchards that cover the low hills: blossoms!

I can't help but think that the blossoms are blooming earlier every year, but it always happens, and my hay fever follows soon thereafter. Still, it is a beautiful sight to see thousands of acres of flowers and deliriously happy bees. California's Central Valley (we call it the Great Valley) is one of the most productive agricultural regions in the world, but it rarely offers much to look at in a scenery sense, or in a geological sense for that matter.

But for a few weeks in the spring, it's a happening place, and is well worth a visit.