Historical geology is a real head trip (remember that term?). Stick geologists in the desert against a cliff like the one above, and they will make a few observations, pick up a few stones (and/or fossils), and in their mind's eye, they will be exploring a long-ago prairie that would have looked much like the one in the picture below (a bit of the rarest ecosystem in California, the prairie at Merced National Wildlife Refuge).
There would be differences of course. This current-day prairie is populated by a diverse group of birds and small mammals like ground squirrels and rabbits. But it lacks some of the components of a healthy modern wild prairie, mainly the larger grazing animals like deer, antelope, and bison, and the large carnivores that would prey on them. Coyotes and foxes still inhabit the region, and cattle or sheep are sometimes brought onto the prairie to help maintain the quality of the grasslands. But the larger canines and cats, i.e. the wolves and the lions, are long gone, as are the bears.
We were on the first full day of our exploration of Death Valley National Park. We weren't there yet, because we had a hundred miles of Mojave Desert to cross before we reached the park. Along the way we made a stop at one of California's most spectacular state parks, Red Rock Canyon (not to be confused with the Red Rock Canyon National Conservation Area outside of Las Vegas). Red Rock Canyon is on Highway 14 between the town of Mojave and Lone Pine, southeast of the Sierra Nevada. The place will look familiar to many, as the striking red and white cliffs have formed the backdrop to dozens if not hundreds of Hollywood movies (including some the opening scenes of the original Jurassic Park).
The plain hills to the south of our parking area (in the picture above) are composed of Paleozoic and older metamorphic rocks that have been displaced and uplifted along the Garlock Fault just south of the park. The rocks have been moved some forty miles from their original location by the left lateral movements of the fault zone. They have their own fascinating story, but what catches the eye are the much more colorful sedimentary layers that were deposited on the eroded surface of the metamorphic rocks between about 8 and 12.5 million years ago, a time period called the Miocene epoch.
For many of our students, this is the first real-world example of the basic principles of stratigraphy. We spent a few minutes talking about the birth of the science of geology in the observations of Nicolas Steno (superposition, lateral continuity, and original horizontality), and James Hutton (uniformitarianism). Then I unleashed them onto the rock exposures so they could evaluate the origins of the rocks and the sequence of events that produced the spectacular cliffs in front of us.
Understanding the changes of a prairie ecosystem through time is as easy as understanding "Saturday Night Live" (which for a fact might not be that easy). For more than forty years the underlying structure of the show has remained much the same; there's a guest host, there is a cold open ("It's Saturday Night!"), there are skits, there is the weekend news, there are fake ads, there are musical numbers. But cast is constantly in flux. There have been many people over the years who have filled in the niches: those who could mimic political figures, those who could act as the "straight man/woman", those who could sing. Sometimes the actors were so unmemorable that they disappeared without a trace after a few weeks or months. Others were successful, and remained for years. Others went on to greater things, like Hollywood movies. And that's how the prairie savanna has worked over the years.
Once our students have looked closely at the rocks, they've identified that there are fine layers representing deposition in lakes, other layers that formed on floodplains or alluvial fans. The terrestrial origin of many of the layers is supported by the bright red color, formed as iron in the rocks oxidized into natural rust. What we don't have time for (or permission for that matter) is a search for fossils, because it is the fossils that tell the fullest story of these rocks. Are these fossils the John Belushi-Dan Akroyd period of the grasslands? Or the Joe Piscopo-Eddie Murphy period? Or Kate McKinnon?
Grasses emerged as a dominant plant species in the middle of the Cenozoic period around 30-35 million years ago. The low-lying plants had a novel method of survival: instead of broad leaves easily chewed by forest-dwelling animals, the blades of grass incorporated silica into their structure, and the hard silica would soon destroy the teeth of most animals that tried to subsist on it. A general warming and drying of the world climate led to the expansion of the grasses at the expense of woodlands and tropical rainforests. Animals either adapted to the new conditions or went extinct. The early part of the Oligocene and early Miocene saw many changing species, especially in the horse clan. The ancestors of the horses were small browsers in the forests. As they adapted to the open grasslands, they became larger, and their feet went from three or four toes to hooves, which gave them great speed to escape predators. Their teeth evolved to grow throughout life, allowing them to survive nicely while grazing the grasslands.
The fossil-bearing rocks at Red Canyon are called the Dove Spring Formation (formerly the Ricardo Formation). The cast of characters are familiar in the sense that they fill the roles of many species on the prairies and wetlands today, but there were some unfamiliar characters as well. More than a hundred species of plants and animals have been found, making this one of the richest and most diverse fossil assemblages in the American West. They include the smallest mammalian members of the ecosystem such as mice, ground squirrels, rabbits and even a pika. The larger grazers were represented by ten (yes, ten) species of horse (compared to the three existing in the present day), four camel species, and three species of antelope. There were the surprising ones, two rhinoceros species, and two elephant ancestors (gomphotherium). The carnivores are represented by eight species of canine ancestors (some are called the "bone-crushing dogs"), and three species of felids (cats), including an early saber-tooth. There is a fair candidate for the ancestor of bears and dogs called a "bear dog" (Amphicyon). For a complete listing of the fossils found at Red Rock, check out this technical report from 2009.
So our investigation of an ancient savanna prairie revealed some of the early players in the drama that has played out across North America over millions of years. Some of the players (genera) were diverse and widespread but ultimately died out in North America (the horses and camels, rhinos and elephants). Other lineages survived, including the deer, the pronghorns, and predators like the wolves, coyotes, mountain lions, and foxes. The bears still lurk nearby in the mountains and would no doubt reoccupy the grasslands if the farms disappeared. Like "Saturday Night Live", the show continues and hasn't suffered cancellation, but a great many changes have taken place. The prairies of 12 million years ago can still be found in California today, but with a new cast and a different look.
River Otter at the Sacramento National Wildlife Refuge
California's Great Valley (called by some less proud people the Central Valley) is the most agriculturally productive place on the planet, producing something like a quarter of the nation's nuts, fruits and vegetables on about 2 percent of the land. The agricultural and accompanying urban development has altered 95% of the original savanna landscape. Prior to the arrival of the Europeans in the 1800s the valley was a vast prairie/grassland that stretched for 400 miles, broken up here and there by a vast network of rivers and wetland marshes fed by numerous streams flowing from the Sierra Nevada.
Raccoon at the Sacramento National Wildlife Refuge
For several million years the valley was the wintering ground for millions, maybe billions of migratory birds that spent their summers breeding in the Arctic. The arrival of humans and their alteration of the landscape disrupted this intricate ecosystem. The birds continued to migrate in reduced numbers and with their natural food sources gone, they started going after the crops being grown by farmers. This became an untenable situation, and there were those who advocating shooting the birds to extinction, but cooler heads prevailed, and work began on establishing a chain of national and state bird refuges at strategic locations up and down the valley. These refuges provide us an idea of the primeval appearance of the valley.
Deer at the Sacramento National Wildlife Refuge
It turns out of course that birds weren't the only creatures displaced by human development. The original valley was a savanna with multitudes of grazing animals and their predators. There were elk, deer, and pronghorns, along with wolves, coyotes, foxes, bobcats, mountain lions, and bears. Prior to 12,000 years ago, there were mammoths, mastodons, giant sloths, saber-tooth cats, and giant short-faced bears. To a degree, the refuges that were originally meant for birds also provide shelter for the remnants of this incredible ecosystem. In my travels, I've seen the elk and deer pictured in this post along with river otters, raccoons, foxes, and coyotes.
Tule Elk at the San Luis National Wildlife Refuge
Today's post was prompted by my sighting yesterday of three River Otters crossing a road at the Sacramento National Wildlife Refuge. They were moving so fast that by the time I was able to raise my camera, only one was left, and I got but a single shot.
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.
