I used to talk to my students about the geological hazards that we face as inhabitants of California's Great Valley (or Central Valley, for those who don't appreciate its actual greatness). I would go down the list of things to worry about: earthquakes, droughts, wildfires, volcanic eruptions, flooding, and so on. But then I somewhat jokingly described things we didn't have to worry about such as hurricanes (Florida's problem), tsunamis (a problem for coastal cities), tornadoes (Oklahoma's problem), and mass wasting (also known by the generic term 'landsliding').
Unfortunately, over the years I've become aware that some of those unlikely hazards actually can be a factor in living in the valley. We've had a fair number of tornadoes in recent years, including two that came within a few miles of my house (they weren't anything like the monsters of Tornado Alley in the Midwest, but still a bit scary). A powerful tropical storm hit Southern California last summer that came up just short of being a hurricane, and the heavy downpours were statewide. And then there is mass wasting (slope failures and landslides). I know of at least two fatalities caused by mass wasting in the last few years. One was a homeless person who had dug a tunnel into a river embankment that later collapsed, and another was a person who was driving along a freeway in heavy rains when the freeway embankment collapsed as a mudflow and spread across the lanes causing a fatal accident.
The Great Valley is famously flat so mass wasting doesn't seem to be much of a danger to those who live here, since landslides and other slope failures require, well, a slope to happen. But the valley is not quite so flat as people may think. The valley is 400 miles long, and most of it is close to sea level. Much of it is low-lying river floodplains, but other sections sit at slightly higher elevations because of complex history of climate change and glacial ice ages over the last 1,000,000 years. These bluffs and terraces protect my city and others nearby because even the worst floods are contained within the floodplains and do not spill over onto the terrace surfaces where cities like Modesto and Turlock have been built near the Tuolumne River.
During the ice ages glaciers never reached the valley floor, but meltwater from the Sierra Nevada glaciers swelled the rivers to several times their average flow, and they carried tremendous amounts of muddy sediment that spread widely across the valley floor building up alluvial fans. When the glaciers receded, the rivers flowed less, but carried clear water that was more capable of eroding the soft sediments of the alluvial fans, forming channels and floodplains several tens of feet deep. Once these channels developed, floods never covered the terraces again. It's the bluffs that form the boundaries of these terraces that provide the conditions that can result in slope failure.
The heavy rains of 2022-23 led to widespread flooding across many parts of California including some real problems on the Tuolumne River Parkway Trail when I regularly go birdwatching. I wrote about these in January of 2023 in the aftermath of one of the biggest storms. The most serious problem was the access road to our town's water treatment plant. It's on the river floodplain about 60 feet below the river terrace. Slumping had caused major cracks to form in and near the pavement.
Eventually the rains subsided and the soil dried up. The slide seemed to stabilize, but the threat to the roadway remained and would eventually have to be dealt with. That is what was new this week: the cranes and were in place to start the slope mitigation process.
The main problem is that the access road traverses unstable debris and soil that slumped in the 2023 event. They would need to re-engineer the slope by rebuilding it from scratch. Their strategy was complicated by the fact that all the equipment and materials had to traverse the very road they were trying to repair. Truckloads of heavy boulders were going down the road every few minutes. Meanwhile a huge long-reach excavator was digging away at the slope below the road!
After digging away and smoothing off the slope they covered it with felt matting and then started piling many tons of boulders on the slope. The boulders are intended to buttress the slope and hopefully keep it stable during future weather events.
It's a lot of work being done to keep a single paved road open, but it's a pretty important road since it provides the only access to the water-treatment plant for the city of Waterford. And thus we are dealing with slope mitigation in what is supposedly the flattest place in the country!
California's Great Valley is many things: one of the most important agricultural regions in the world, America's Serengeti Plains where millions of migratory birds spend the winter, and one of the most polluted air basins in the country. The pollution is a shame, causing all manner of health problems for those who live here, and obscuring the incredible mountains that ring the valley. Except on a few select days out of the year. Today was one of those days.
Gray, Red and Merced Peaks in Yosemite National Park
We had a fairly intense storm last night, and it was followed up by windy cold conditions that cleared the air. I took my customary walk along the Tuolumne River Parkway Trail. A section of the trail follows the bluff and on days like this, I get a wonderful panorama of the Sierra Nevada covering Yosemite National Park. A zoomed-in look provides a view of Gray, Red and Merced Peaks in the southern part of Yosemite (above).
A shift to the north reveals the high peaks of the Sierra Crest, including Mt. Maclure, Rodgers Peak, and Mt. Lyell, three of the higher peaks in Yosemite National Park (Mt. Dana, the 2nd highest, isn't visible). Some of the foreground peaks are rather famous as well. Mt. Starr King and Sentinel Dome are visible, and at the very left edge of the photo is the top portion of Half Dome! It's hard to pick out, but the CalTopo provides some identification of the different peaks.
Once a week, my errands take me past the intersection of Keyes and Hickman Road on the floor of California's Central Valley. There is usually nothing much to be seen there in the late afternoon hour, just some fields of crops and almond orchards. Nothing much that is, except for the rare clear days in our usually smoggy and dusty valley. On those days, the Sierra Nevada can be seen off in the distance, and from a narrow angle, one can see the looming edifice of Half Dome, rising 4,000 feet above Yosemite Valley. Today was one of those days.
It's been a little controversial, because there are some who think it is not possible to see the dome, and indeed it is not easy to see unless you know just where to look. My pictures are at zooms ranging from 60x to 120x. The picture below provides an idea of the appearance with the naked eye. The dome itself is mostly to the left of center. One has to keep in mind that the rock is something like forty miles away, and there are even effects caused by the curvature of the earth that make it look odd.
The previous day had been clearer, but I just couldn't get away to try for the picture. I had to sharpen the contrast and play with the other settings to bring out the dome. Some are surprised that it doesn't form the skyline, but the peaks behind reach elevations of 12,000 feet or more. Half Dome isn't even 9,000 feet high. I only discovered the view because the first time it was visible to me, there were clouds obscuring the peaks behind, causing the dome to stand out as if it were on the skyline.
We'll see if the storms next week clear out some of the dust and smog...
There's a difference between apologetics and polemics. The latter is an attack, but the former is a defense. I was writing a piece at my other blog, Geotripper's Birds of California about Sandhill Cranes, and in a few paragraphs it turned into an apologetic for living in the Great Valley of California, a place that few people find attractive. The thing is, when one searches carefully, there is much to see here in the way of beauty and grandeur. The Sandhill Cranes are but a single aspect. The original post follows:
These beautiful birds are among the reasons I took up bird photography a couple of years ago. I was astounded to find that Sandhill Cranes (Grus Canadensis) congregated by the tens of thousands very close to where I live, and I was not the least bit aware of it.
Living in the Central Valley of California (which I agree should always be called the Great Valley) is an exercise in frustration and futility. The natural environment, the greatest savanna environment in the United States, was almost completely co-opted by agricultural development, and then by urban development. It's not a great place for people to live...most of the jobs are poorly-paid manual labor, the soil, air and water are infused with pesticides, herbicides, and particulate air pollution, and health problems, especially asthma and related respiratory illnesses are rampant. Education is a low priority to those in power. We are consistently the first to suffer in economic downturns, and the last region to recover from them.
And yet there is still a greatness to this valley. In terms of the natural environment, dedicated people have worked tirelessly for decades to preserve the remnants of the rich ecosystem, and have worked even harder to rebuild some of the habitats as abandoned farmlands have come available. Thousands of acres of river floodplains have been replanted with native vegetation. There is now a string of wildlife refuges along the 400 mile length of the valley that provide shelter for the millions of winter migrants, the Sandhill Cranes, the Aleutian Cackling Geese, the Snow and Ross's Geese, and many others.
The Great Valley that existed hundreds and thousands of years ago is still available to observe and enjoy, and often only a few miles from the homes of everyone who lives here. In the Modesto-Turlock area, there are the San Luis and San Joaquin River National Wildlife Refuges. The Beckwith Road viewing platform (part of the San Joaquin refuge) is only an eight mile excursion from Modesto's biggest shopping mall. I was there last night and had a real treat. The Sandhill Cranes are elegant large birds, beautiful to photograph, but they are a bit wary (with good reason) of human beings. They tend to stay towards the interior of the refuge, being heard more than seen off in the distance.
It's deep into winter now, and food stores are kind of low. The refuge managers grow fields of corn and other crops for the sole use of the birds, and they'll plow down the corn in sections so the birds can feed easily. Once those crops are gone, the birds make do, and last night they were roaming the plowed fields close to the road and viewing platform. I got some of my closest shots in a long time.
This is part of the valley as it once was, and still is. It belongs to all of us, and it is right in our own backyard. And to our coastal and urban center friends, don't forget that there are some incredible sights to see on the valley floor when you are on your way to Yosemite or to one of the Sierra ski resorts. For our international visitors, there are more places to see than the travel brochures hint at. If you are interested in the natural world want to see some of the real California, not just the tourist meccas, then check out these places. The refuges are worthy of a look.
The fog here in the Great Valley is legendary. The so-called Tule Fogs can last for weeks, hiding the land in an impenetrable mist. People who would panic at the thought of driving with their eyes closed continue to speed through these fog banks where the visibility is measured in feet rather than tens of feet. One such accident in 2007 involved 90 cars and 18 big-rig trucks, with two people killed.
The Tule fog is a radiation fog, caused when heat from the ground radiates into the atmosphere at night, cooling the ground and causing condensation to take place. The fog persists as long as the temperature doesn't rise, and in the Great Valley, ringed is it is by high mountains, the conditions may persist for weeks at a time. Stable motionless air develops an inversion layer that can be difficult to break up unless a large storm blows in.
I was not prepared for the fogs when I made the valley my home nearly 30 years ago. I hated the gloomy days that seemed to never let up for weeks at a time. I had frightening near-misses on the highways. I even got lost a few times in the pre-GPS days, getting disoriented on backroads that were poor in signage. I was known to drop important projects and drive into the Sierra Nevada foothills for the sole purpose of getting into the sunshine. I hated descending back into the soupy mess.
The drought in California has caused a drop in the number of foggy days, since wet ground is a major requirement for forming the hated mist. Global warming plays a role, as warmer conditions are less likely to result in foggy conditions. Temperatures in some parts of the Great Valley are up by 3 to 4 degrees Fahrenheit. According to one report, the number of foggy days in Fresno declined from an average of 37 in 1980 to 22 in 2014. This has been a two-edged sword: besides the reality of the drought itself, the lack of cold wet conditions have caused a drop in agricultural production, as a number of fruit trees like cherries and peaches require the cold dark days to help the trees go dormant in winter.
I'm seeing fog on the early mornings when I make my way to work through the pasturelands outside my village. They've added an aura of mystery to the landscape, and haven't yet interfered with my driving, so I'm seeing beauty right now. We just finished a series of storms, and conditions will be stable and calm for the next 10 days or so. We'll see how I feel if and when the fog sets in.
Now that I've got your attention, let's get to the post (explanation below)
In the great Central Valley of California there are only two seasons -- spring and summer. The spring begins with the first rainstorm, which usually falls in November. In a few months the wonderful flowery vegetation is in full bloom, and by the end of May it is dead and dry and crisp, as if every plant had been roasted in an oven.
John Muir, My First Summer in the Sierra
It's true, really. Winter doesn't exactly happen in the Great Valley (called by some the lowly Central Valley). While much of the country lies buried beneath snowdrifts, and people wait longingly for the first signs of spring somewhere around March, we watch the grass growing. Sure, we have some deciduous trees that turn bright colors and drop their leaves (still waiting for that to happen, by the way), but many of our oaks are evergreens. As Muir noted, the spring begins with the first rainstorm. He mentioned November, but our storms came a few weeks early. And like magic the parched valley is already turning green again.
For various reasons, it's been about two weeks since I've walked our nice little river trail where the Tuolumne River leaves the Sierra Nevada and flows into the Great Valley. The last time I was there, the landscape was parched. It had been nearly six months since any rain had fallen in the area, and it showed. There were weeds and dry grass everywhere, and every step raised a puff of dust. Then "the storm" happened, a record-setting late October storm that dropped two inches of rain in two days. A few days later, the green grass was sprouting everywhere. There is an entirely different feel to the Parkway Trail now.
I lived in an area that had winter seasons once, spending two years in Reno, Nevada, at 4,500 feet. I recall driving from Reno into the Central Valley at Christmas, struggling through a snowstorm on Donner Summit. When we reached the valley floor, it was warm (!), and I could smell the chlorophyll in the air. The greenery was stunning after what had been a month or more of snow storms. And that's what central California is like for most of the winter. It's the reason that Arctic birds like the Sandhill Cranes and Snow Geese like to spend the winter on the valley floor. They have access to food throughout the winter.
The storms of course had a huge effect on the river flows in the Sierra Nevada. Last weekend, we saw the effects of the rain in Yosemite Valley. The runoff of the Merced River resembled flows in early spring (at least for a few days). The Tuolumne River was less changed. The flow of the river is controlled by the turbines of Don Pedro Reservoir, a huge dam about 20 miles upstream. The river flows through a number of pools, and the reflections of the sky were beautiful. This was the spot where I saw some River Otters a few weeks ago (you can be sure that I'm always watching for them).
The water was so calm and peaceful. Occasionally a Hyacinth floated by, which explains the picture at the top of the post (turn the picture upside down and it will make more sense). The Hyacinth is actually a scourge throughout the rivers of the Great Valley. It is an introduced species that grows rapidly and chokes river channels. It causes oxygen levels in the river to plummet and many animal and plant species can't compete with the weed. The drought exacerbated the problem, as the rivers were not able to flush out the channels of the weed. Luckily, this year there was a bit of extra water, allowing higher surge flows that seemed to clear some of the channels. There is certainly less hyacinth along my stretch of the river.
It was nice to be home for a few days! We'll enjoy our "spring" for a while. When spring arrives for most other people, we'll be sliding into the dry summer season, and then I'll be jealous of you...
Red-shouldered Hawk at entrance to the Sacramento National Wildlife Refuge
Every so often, I remember what an extraordinary place I live in. It's sometimes easy to forget while dealing with the air pollution, the lingering drought, and the seemingly non-ending recession, but California's Great Valley is one of the most important provinces in the United States. It provides something like 25% of the nation's fruits and vegetables, and is the world's leading producer of almonds and a number of other products. Despite being almost completely altered by agricultural and urban development, a few remnants of the original landscape survive. It's a reminder that America once had its own version of the plains of the Serengeti (translation: "endless plains").
Along the auto tour route at the Sacramento National Wildlife Refuge
The Great Valley extends for 400 miles from Redding to Bakersfield, averaging 50 miles in width. It is extraordinarily flat, with most parts lying below 300 feet in elevation. Practically the only exception is an extinct volcano called the Sutter Buttes north of Sacramento, which rise some 2,000 feet over the valley floor. The mountains loom on the horizon of the Sacramento National Wildlife Refuge, where I paid a visit a few weeks ago. It was like exploring the Great Valley in another geological age.
The refuge is a year-round home for many species, but it really comes alive during the winter, when tens of thousands of migratory birds arrive from the far north. A seven mile-long auto route allows for a leisurely exploration. It's a great place to be introduced to the natural landscape of the valley, although there are many others that are equally spectacular (the Merced, San Luis, and San Joaquin being other excellent choices). I just happened to take most of these pictures during my visit at the Sacramento NWR last month.
Gadwalls at the Sacramento NWR
The Great Valley originated as a shallow sea along the subduction zone and trench that dominated the western coast of the North American continent for more than a hundred million years during the Mesozoic Era, the time of the dinosaurs. The sea occupied a sedimentary trough called a forearc basin. As the basin filled with sediment, the weight of the layers pressed the crust downward, allowing more sediments to accumulate. Over time, vast thicknesses piled up, in places reaching 25,000 to 50,000 feet (7,500 to 15,000 meters).
Northern Pintails at the Sacramento NWR
The subduction zone began to transform into a new plate boundary beginning about 30 million years ago. Instead of the convergence of the crust, the plates began to slide laterally, forming the San Andreas fault system (this type of boundary is actually called a transform boundary). The crust along the transform crumpled, causing the uplift of the Coast Ranges just a few million years ago (the mountains are among the youngest ranges in the world). The shallow sea receded and became dry land in recent geologic time.
Ring-necked Pheasants are masters of camouflage...well sort of.
The valley has a Mediterranean climate, with warm dry summers and cool (but not cold) wet winters. The amount of precipitation ranges from very low in the south to relatively high in the north, but for the most part the ground cover is a grassland savanna, with oak woodlands in the wetter areas. Numerous rivers flowing from the adjacent Sierra Nevada supported mile after mile of riparian habitats and wetlands. Swamps and marshes dominate the delta of the Sacramento and San Joaquin rivers. These environments provide habitat for a staggering variety of wildlife.
The original prairies supported vast herds of elk and pronghorns, along with deer, and numerous smaller species of rodents. In earlier times, the landscape supported mammoths and mastodons, bison, ground sloths, horses, and camels. When humans arrived, this rich habitat was forever changed. Many of the species went extinct, or were driven elsewhere. Only about 5% of the original landscape remains.
Despite the horrible destruction of the original ecosystem, patches survived. The vast flocks of migratory birds, though much diminished, still flew into the valley and occupied what corners they could. Members of a subspecies of the elk endemic to the valley, the Tule Elk, were once common across the valley floor. They were hunted mercilessly for hides and meat until they were thought to be extinct around the 1860s. A single breeding pair was discovered in 1874, and after twenty years only two dozen of the elk survived in a single refuge in the south valley.
Ring-necked Ducks at the Sacramento NWR
In the early 1900s, a new ethos emerged, the idea that humans needed to nurture and protect the ecosystem that sustained life on the planet (although few at the time would have worded it this way!). In some cases, the actions came about because favored species had become depleted from over-hunting. In other cases, it happened because migratory birds were damaging agricultural fields because they had no other sources of food. Whatever the reasons and motives, the result was the establishment of hundreds of wildlife refuges across the United States. A series of refuges span the length of the Great Valley like a string of pearls. Animals once on the edge of extinction were brought back from the brink. The Tule Elk now number in the thousands. The Aleutian Cackling Goose, also once thought extinct (a flock of 600 survived on a remote and rarely visited island) number in the hundreds of thousands. The refuges have played a pivotal role in survival of dozens of endangered species.
It is an amazing privilege to experience a place like the Sacramento National Wildlife Refuge (and the dozens of others across the valley) in fall and winter as the migratory flocks arrive. I was stunned to find that this incredible movement of birds was taking place here literally under my nose (okay, over my nose) during the first 25 years I was living here. I was so busy exploring the more showy Sierra Nevada or California coastline that I failed to recognize the treasure that lay just a few miles away from my backyard. I can barely describe the noise of tens of thousands of birds taking flight all at once. It's not just their calling back and forth. It's the sheer compression of all those wings beating at once.
The Snow, Ross's, White-fronted, and Cackling Geese are the very visible and charismatic parts of the ecosystem of the valley, but they are only part of a chain that includes many other species of plants and animals. The challenge of the refuges is in re-creating and sustaining the entire "circle of life", as certain Disney movies might put it. With this basic challenge there is a myriad of conflicts and compromises with the many other stakeholders of our valley, especially when it comes to the issue of water.
Ross's Geese at the Sacramento NWR
My videos from the Sacramento NWR didn't quite work out, but a week later I caught the same species of geese at the San Joaquin National Wildlife Refuge. There are thousands of them taking to the air all at once.
There is another critical part missing from this ecosystem. It's the loss of predators. There are still birds of prey like the Red-shoulder Hawk at the beginning of the post, and the Red-tailed Hawk below. There are the occasional foxes and coyotes that have learned to survive among the human invaders. People have brought their cats and dogs. But the valley was once home to the California Grizzly Bear, the much-larger Short-faced Bear, the American Lion, the Sabertooth Cat, and the Dire Wolf. These animals died out at the end of the Ice Age, although the Grizzly survived into the 20th century. When the large grazing animals disappeared, so did the larger predators.
Red-tailed Hawk at the Sacramento NWR
The Great Valley is a challenge. It's a challenge to live here, it's a challenge to fully understand. In the face of so many land-use issues, it is challenge to one's sanity. But it is also a fascinating place, one that retains a precious link to the past, when it was a functioning ecosystem with a diversity of animals and plants that was the rival to any African savanna. It's worth the effort to explore and understand this landscape.
If you are one of my Modesto-area readers, please be sure to pay a visit to the Great Valley Museum of Natural History. The new museum is a wonderful resource for beginning to understanding the valley as it is and how it once was.
I tell my students on occasion that they live in a place that is relatively free of the most serious geological hazards. We are a fair distance from the earthquake faults that wreak havoc on the coastal cities (the San Andreas and Hayward faults, for instance). We mostly live on a river terrace so serious floods do not impact most of the city (the floodplain developments are an exception of course). We live far from volcanoes or steep slopes that can fail. But I also warn them that there is no place in the world that is entirely free of geologic hazards. I got reminded of that today. A tornado touched down just a few miles from my house, causing some serious damage, but thankfully no one was hurt. Friends were witness to the event. It was uncomfortably close.
Tornadoes are not all that rare in California. No one could mistake our funnel clouds for the monsters that regularly roar down through Tornado Alley in the central United States, but there have been 403 confirmed events between 1950 and 2013. The majority have been weak, as only 25 of them reached EF2 or more. But they do happen, and there was enough energy in the latest storm to produce one this afternoon.
It's been a wild weather month here in central California. I went walking to see the retreating edge of the tornado-forming storm from the new parkway they're building along the Tuolumne River. It's looking very different than it has for most of the last four years. It's wet. Ponds of water covered parts of the recently aligned trail.
We've had three major storms in as many weeks, and they followed two weaker storms last month. The month is half over, but it is already the second wettest November in the twenty-five years I've been keeping records at my home east of Modesto in the Great Valley. We've received 2.48 inches, which is equivalent to nearly a fifth of year's normal precipitation. It would be nice if this were a harbinger of more storms to come. We've been in the throes of the worst drought in the historical record. Last year's snowpack in the Sierra Nevada amounted to less than five percent of normal. Our reservoirs are just about empty, and the shortfall would not be made up even if we had a record year of precipitation.
As much as we hope for an end to the drought, it's a clear case of being careful what you wish for. El Nino weather years are known for producing intense weather events, causing flooding and mudslides in central and southern California. And the El Nino that has been building in the Pacific Ocean this year is a record-breaker, a storm-maker on steroids. Our storms so far haven't even been warm storms out of the south. The main effects aren't really expected for another month or so.
As I walked this afternoon, I noted that there was already a small slope failure along the trail. It did no damage, but it's a warning of what may be coming. I was reminded of the floods of 1997 when the Tuolumne River was flowing at 70,000 cubic feet per second, the highest ever recorded. The river threatened numerous bridges, and flooded more than 1,000 homes downstream. And the flood could have been worse had Don Pedro Reservoir upstream hadn't held back the highest flows (at one point, the inflows exceeded 130,000 cubic feet per second).
One thing I am anxious to see happen is a high enough runoff to scoop out the hyacinth plants that are threatening to cover the river. The invasive weed crowds out the native plants, blocks light from the river bottom, and lowers the oxygen content of the water. It's been around for years, but the infestation has been particular bad in this year of constantly low flows.
I turned around and reveled in the sunset and fall colors that have finally arrived. I know that a lot of you live in places where the fall colors are astounding and all, but California is simply a darn nice place to live, despite all her problems. Here I was walking in a light shirt and short pants, in the middle of November still enjoying the changing leaves of the trees. I can visit snow if I want to, but I won't be shoveling it. It's been a tough four years of drought, but maybe the tide is turning. A record wet November is certainly a good start. I can do without the tornadoes, though.
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