A cinder cone in Lassen Volcanic National Park

The Natural History of the Sierra Nevada

Perched on Half Dome in Yosemite National Park after the climb of your life, you might spend an indolent hour imagining glaciers occupying the steep, granite canyons of this breathtaking vista. On your way up the dome, you touch places that were scraped by a glacier in the past 1 million years.

Venture to the edge of Half Dome and peer down 4,000 feet to Yosemite Valley. You can see where the rock cracked and broke as smaller glaciers flowed at the foot of the dome.

But it's not so easy to imagine what this scene looked like before glaciers and granite. From the top of Half Dome, you probably will not find a hint of an ocean in the eroded cleavages of Yosemite's cliffs. Even if you know the history of the Sierra Nevada, it is difficult to imagine coral, starfish, and coiled cephalopods in salt water where Yosemite Valley is now. Yet, if you were looking back about 400 million years ago into a Paleozoic panorama, you would see the Pacific Ocean and small sea creatures.

In the 4.5-billion-year history of earth, you would not be looking back very far. The 400-mile-long and 60-mile-wide Sierra Nevada is a young mountain range, and it is still rising. The origins of the Sierra—the longest continuous mountain range in the United States—can be traced to the Pacific Ocean before California existed.

Click here for a new window with a large version of this map.The North American West Coast was well east of the present-day Sierra, perhaps in Utah. The evidence of an ocean covering present-day California is still in the Sierra. Geologists have found marine sedimentary rocks—carbonates, such as limestone—dating back about 400 million years in the Eastern Sierra around Convict Lake and other places. Sediment from the North American continent had been eroding into the ocean for millions of years during a relatively quiet and stable geologic time. As the sediment layers cemented together, the continent was slowly extending into shallow sea floor.

But the quiet time was coming to an end. In the tumult to come, many of the sedimentary seabeds would be pushed vertical or squashed together in ways that seemed impossible to understand when geologists studied them in the nineteenth century. Today, scientists believe Plate Tectonics—the theory that continents drift on pieces of the earth's crust—set many changes in motion, including volcanoes, earthquakes, and mountain-building episodes.

Starting 400 million years ago, the volcanoes erupted sporadically for many millions of years off the coast of the North American Plate. Arc islands, similar to the environment of present-day Japan, began forming. Then, a mountain-building episode began around 230 million years ago, which some scientists believe marks the beginning of the White Mountains east of the Sierra. The activity occurred at the beginning of the Mesozoic Era as the earth's continents began to break apart from the single super continent known as Pangea. The North American Plate separated from Africa and Europe along the Mid-Atlantic Ridge. The North American Plate drifted west, colliding with the Pacific Plate.

These plate collisions develop belts called cordillera at the fringes of continents. On the western edge of the North American Plate, the Sierra today exists in a vast cordillera running south from Alaska to Tierra del Fuego. Its origins can be traced to the Mesozoic collision between the North American and Pacific Plates.

The thinner Pacific Plate was forced to dive below the North American Plate in the collision. On the upper side of the Pacific Plate, many miles of rocks melted and became magma. Some magma rose to the sea floor and erupted as volcanoes. But some magma remained below the surface, cooling and crystallizing into the granite that later was uplifted to become the White Mountains, which are east of the Sierra and Owens Valley.

Rainbow trout (Oncorhynchus mykiss)About 80 million years later, the North American Plate began moving faster and forcing a larger piece of the Pacific Plate to submerge. Chunks of the ocean floor and the continental plate were violently broken, folded, and forced upward to create an ancestral Sierra range, which rose perhaps 15,000 feet above sea level. Remnants of the ancestral range can still be seen in rock pendants today, but this early-day Sierra is not the massive batholith now visible.

The current Sierra batholith was forming below the earth's surface in huge plumes of magma that were created by the accelerating collision of tectonic plates. Much of this magma did not surface. Instead, it cooled and crystallized into giant blobs of granite that would rise millions of years later. From about 150 million years ago until about 80 million years ago, such granite magma pulsed dozens of times to create this batholith. It subsided and remained below the earth's surface until erosion and uplifting episodes began raising it about 30 million years ago.

During the time the batholith cooled, rich veins of gold and silver were laid down in the large cracks and crevices of the granite. As the granite cooled, heated quartz solutions rose and filled the fissures. Besides gold and silver, the quartz contained jade, copper, and other minerals. These large veins of quartz would later be bared through erosion. Gold and other metals were washed into streams, as any gold miner in the 1840s would attest. Huge deposits of the quartz remained buried in hillsides where miners would excavate it in the nineteenth century.

But the gold and the granite magma of today's Sierra were still beneath the earth 120 million years ago when tremendous erosion began on the 15,000-foot-high ancestral Sierra. The range was lowered to about 3,000 feet at its crest 60 million years ago. At about the time the dinosaurs went extinct, the Sierra was a collection of gently rolling hills in an area with a tropical climate. Much of its rock settled as alluvial deposits in the 400-mile Central Valley, which was still covered by the ocean.

The Mesozoic rocks of the ancestral Sierra are classified as metamorphic because they have changed, or metamorphosed, over time. They changed from such rocks as sandstone and shale to slate and schist. They are similar to their Paleozoic predecessors, but they can often be distinguished in the Sierra high country by the color on their exposed surfaces. These types of rock are usually gray, while the exposed Paleozoic rocks are reddish. One of the better places to find the Mesozoic rocks is in the Eastern Sierra on the John Muir Trail near Shadow Lake.

Sierra rocks are tougher to identify than it sounds, though. A lot of volcanic and earthquake activity took place from 30 million years ago until about 12,000 years ago, and parts of the Sierra are a virtual mosaic of different rocks. In the Northern Sierra, for instance, geologists found Cenozoic volcanic rock along with Paleozoic and Mesozoic metamorphic rock. Some of the oldest rock is on top of the younger rock.

There is plenty of debate about what happened to push the Sierra into its present-day configuration. It is generally agreed that volcanoes and uplifting episodes, which include massive earthquakes and other forces, worked together. The two did their most dramatic work over the last 10 million years, but they began to shape the present Sierra about 30 million years ago.

Violent volcanic eruptions began in the Northern Sierra as magma pushed up from the diving Pacific plate. The process produced three types of volcanic rock—andesite, basalt, and rhyolite. Andesitic lava has light and dark minerals in it, and is thick, so it tends to flow only short distances. Basaltic lava, filled with iron and magnesium, flows easily and travels greater distances but it normally is not associated with explosive eruptions. Rhyolitic lava is similar to granite, and resists flowing. Rhyolite is the type of rock found around explosive volcanoes, such as Mammoth Mountain.

Rhyolite can be found north of Yosemite National Park throughout the Sierra, where explosive volcanoes erupted about 30 million years ago. The explosions died down after about 10 million years, but another dramatic explosion took place in more recent times at Long Valley Caldera, a 19-mile-long and 10-mile-wide depression still visible today. During the explosion about 700,000 years ago, rhyolitic ash rained on the countryside, as the explosion flashed at perhaps 100 miles per hour. Scientists believe the temperature in the middle of the caldera was between 600 and 750 degrees Fahrenheit.

The Sierra landscape also displays andesite, especially in the Central and Northern Sierra. Andesitic eruptions followed the Northern Sierra rhyolite events about 20 million years ago and produced rough, chunky rock formations. In the Central Sierra, thick andesite features can be seen at the Dardanelles Cone in the Stanislaus National Forest. Donner Summit in the Tahoe National Forest also contains similar features.

Basalt remnants can be seen on the Eastern Sierra. In the Mammoth Lakes area, a 600- to 700-foot basalt flow moved down the ancient San Joaquin River about 100,000 years ago. The flow created the Devils Postpile—bizarre-looking vertical columns that are considered one of the most geometrically regular remnants in the world.

During the volcanic fireworks, how did the huge Sierra batholith rise? The possible answers to that question cause a lot of arguments. In general, scientists believe erosion of the ancestral range and episodes of earthquakes explain the appearance of the newer granite. The most imaginative arguments usually focus on where and when the uplifts occurred. But there is no argument about the power of earthquakes to lift the mountain range.

In 1872, Lone Pine in the Owens Valley, just east of 14,497-foot Mount Whitney, was virtually destroyed, and 27 people were killed in a quake that raised part of the Southern and Eastern Sierra 13 feet. If only one such quake happened every 1,000 years, the Southern and Eastern Sierra would grow 13,000 feet higher in just 1 million years. Between the sinking Owens Valley and the rising Sierra over the last several million years, there has been a displacement of about 19,000 feet from the crest to the Owens Valley block. Only about 11,000 or 12,000 feet of it can be seen because the rest extends beneath the soil to the valley block.

The Northern Sierra is a slightly different story. It had risen close to its present height about 2 million years ago. The rise came mainly on the eastern side of range as faulting tilted the Sierra to the west. The western edge of the Sierra's subsurface block disappears beneath the Central Valley floor where it encounters the block from the Coastal Range. Like the rest of the Sierra, it is still rising.

How high could the Sierra rise? The simple math is staggering. Erosion takes about 18 inches from the mountains every 1,000 years. If the range is rising 13 feet or more every thousand years, the Sierra could one day be the world's tallest mountains.

Add Ice

About 30,000 years ago, the Grand Canyon of the Tuolumne River was on ice—actually, under ice, about 4,000 feet of it. The canyon is just north of the world-famous Yosemite Valley, which also was buried in ice at the time. This was the height of Sierra glacial advances in the Ice Age, and the Tuolumne River had the biggest Sierra glacier of them all. In addition to being 4,000 feet deep, it was 60 miles long, creating a monumental, low-speed battering ram moving only inches or feet per year. This and other Sierra glaciers transformed V-shaped valleys into U-shaped valleys with all the urgency of a tortoise taking a morning stroll. It could take centuries for a glacier to move 0.5 mile.

But, in geologic time, this mountain-altering process moved at the speed of a frightened deer compared to the Sierra's previous history. The granite that began forming in the earth 150 million years ago was drastically changed in less than 3 million years. It would be like catching the last three minutes of a 2.5-hour movie and seeing some of the most exciting developments.

The Sierra, like the Rocky Mountains and the Cascades, was high enough 3 million years ago to stop great glaciers advancing from Canada and the rest of North America. But because it was so cold in summer, the Sierra formed its own glaciers. Over many years, snow began melding together into what some geologists consider a metamorphic rock made of hardened ice. It is called "firn," which is pre-glacial ice that does not thaw in summer. Today in the Sierra, scientists refer to the "firn limit" as the lower edge of compacted snow that does not melt.

yellow-bellied marmot (Marmota flaviventris) At the approach of danger, including predators such as the eagle, the yellow-bellied marmot retreats toward its burrow, usually located beneath rocks.To build a glacier, about 100 feet of snow must accumulate and harden to start downhill in a canyon already cut by a stream. The glacier is not a solid block of ice, however. The upper levels of a glacier can be fractured with cracks that can develop into crevasses. Large crevasses can be as deep as 200 feet. Crossing any large glacier can be hazardous because overhanging snow can mask a crevasse, though the small Sierra glaciers today probably do not present the same hazards as those in Alaska and other parts of the world.

The largest glaciers in the Sierra occurred from Donner Pass south to the Kern River canyon. Major watershed basins, such as the San Joaquin, Kings, and Kaweah in the Southern Sierra, had extensive ice fields and glaciers. There were four periods of glaciation and long periods of interglacial warmth in the Sierra.

The massive glaciers did a lot of grinding, scraping, and polishing on the Sierra granite. In the process, the heavy ice would gouge the bedrock, picking up pieces of rock and carrying them. As the glacier moves, it would leave debris on either side in a pattern called a "lateral moraine." When glaciers melted, they also would drop the debris heaps called terminal moraine. Visitors to Yosemite Valley can see a well-defined terminal moraine in Bridalveil Meadow.

Yosemite Valley contains many of the most spectacular effects of glaciation, including large waterfalls. Bridalveil Fall, for instance, was created when a glacier shaved off the mouth of Bridalveil Creek at the place where it entered Yosemite Valley. The creek was left suspended high above the valley floor, forcing it to take a misty plunge now enjoyed each spring and summer by millions who visit Yosemite National Park.

Other glacial signatures, such as erratics or rocks left behind in odd places, can be seen in the Sierra. Fallen Leaf Lake, next to Lake Tahoe, is a glacial remnant. It is a moraine-dammed body of water created when a departing glacier dropped its granitic debris along a stream.

The last Ice Age ended about 12,000 years ago, and the large Sierra glaciers departed some time later. The 65 or 70 small glaciers now occupying the Sierra are not more than 4,000 years old, and none are more than 1 mile long. The largest are on Mount Lyell in Yosemite and the Palisades in the Eastern Sierra.

Rivers and Rainfall

Rivers, the conduits of glaciers and carriers of sediment from eroding landscapes, have been around longer than the Sierra. Flowing from North America west to the Precambrian ocean, rivers have been doing their job for about 1 billion years on this part of the globe, although rivers have existed for a much longer period.

Rivers are important in the Sierra, as in any mountain range, because they are quite literally the main drains for anything washed off the landscape—common sediment, gold, boulders, trees, and other material. They also do the heavy work of cutting canyons in granite.

If not for such erosion processes, the range would have grown much taller in the last 5 million years. Mount Whitney might be higher than Mount Everest, which is more than twice Whitney's present height of 14,497 feet. Oxygen and water in the atmosphere simply wear down the mountains, chemically assailing the rocks. Rivers are collectors of the water and the debris dislodged in the erosion process. The erosion and the rivers depend on California's winter storm cycle.

The western slope of the Sierra is usually battered by winter storms from November through April. The name Sierra Nevada literally means "snowy mountain range" in Spanish. The Sierra is one of the snowiest places anywhere in the United States. Locations above 8,000 feet in the Central Sierra routinely record more than 35 feet of snow annually, and big winters can produce more than 70 feet in many high-elevation meadows.

The storms incubate in the Pacific Ocean and move east into the Pacific Northwest and California. When a moist ocean air mass—a storm front—reaches the Sierra's western slope, it must begin climbing or rising to get over the mountains. As it rises, the air mass cannot hold as much moisture, so it must drop moisture as rain. This can sometimes be orographic precipitation, or rainfall that occurs in the mountains but not down in the Central Valley. Once a Sierra storm rises to about 7,000 feet, it begins to drop snow.

But, by the time the storm clears the Sierra crest and begins descending the sheer east side of the range, it begins to quickly warm up, lose altitude, and stop dropping precipitation. The Eastern Sierra receives much less precipitation than the western slope. Generally, the major streams on the western slope are much longer and flow more consistently than the Eastern Sierra streams.

The western-slope rivers can sometimes be intimidating. During a 1950 storm, the 265-mile American River in the Central Sierra had a peak discharge of 180,000 cubic feet per second or 90,000 acre-feet of water in one day. That single-day runoff would be enough water to supply a California city of 100,000 people for a year. The American River drains about a 2,000-square-mile watershed. In contrast on the east side of the crest during the same 1950 storm, the 60-mile Truckee River peaked at about 17,500 cubic feet per second.

Between 1 billion and 400 million years ago, such peak flows amounted to little more than a deep cleansing on the western edge of North America. In the early Paleozoic Era, plants began to appear, and peak-flowing rivers meant fresh sediment would be washed into new areas to help spread and renew vegetation. Boulders would be rolled downstream and shattered to create gravel where trout would later spawn. Many other benefits would accrue for the ecosystem.

But, in the last 100 years, as people began to dam the major rivers of the Sierra, the peak flows became destructive floods. Dams cannot tame the biggest floods on the Sierra, and a large amount of water occasionally must be released from the dams during large storms. The result is billions of dollars in damages to homes and downstream land where people build and farm too close to rivers. Ultimately, many have died in floods. The floods are still a boon to the ecosystem, but people sometimes tragically underestimate Sierra rivers.

The Life Zones

Imagine traveling north from the great southwest deserts of the United States to northern Canada. The vegetation, animal life, and landscape would change remarkably for several reasons, including precipitation, temperature, soil, and geological features affecting the wind currents. But you wouldn't need to travel thousands of miles to see similar kinds of changes. Different elevations of the Sierra exhibit most of the same shifts in response to climate changes. As you ascend the Sierra and the air temperature drops, you find differences in the plants and animals. You pass through the Sierra's life zones.

American zoologist C.H. Merriam first noted the different zones of life that appear as he ascended the mountains of northern Arizona. Scientists do not suggest that the same vegetation and animals found in life zones of one mountain range would be found in others. The life within the different elevation zones of the Rocky Mountains differs from those in the Sierra Nevada. There are differences even from the Eastern Sierra to the western slopes of the Sierra. But the concept of life changing from zone to zone holds true for any mountain range.

The Sierra life zones have been sliced and parcelled a number of different ways, but one of the more universal views is that there are five distinct zones determined by elevation. For the western slope, they are the foothill, lower montane, upper montane, subalpine, and alpine zones. The eastern slope zones are the same except for the lowest zone, which is called pinion-sagebrush. The pinion-sagebrush zone is an adaptation to a drier climate, and it is ranges up to 7,000 feet compared to the 3,500- to 4,000-foot high point for the western slope foothill zone.

On the western slope, the lower montane ranges from about 3,500 feet to 6,000 feet. The upper montane runs from 6,000 to about 8,200 feet. The subalpine goes from 8,200 to about 10,500. The alpine is designated from 10,500 to above 13,000 feet. The elevations are similar on the Eastern Sierra, but slightly higher in elevation. The lower montane is compressed between 7,000 to 8,000 feet. The upper montane is between 8,000 and 9,000 feet. The subalpine is 9,000 to 11,000 feet. The alpine is 11,000 to above 13,500.

The higher the life zone, the shorter the growing season for plants. In the highest life zones, the subalpine and alpine, plants may only be able to grow seven weeks of the year. The rest of the year, prolonged freezes make plant growth difficult or impossible. Larger mammals, such as bears or mountain lions, do not generally live in the higher zones because there is not enough plant life to sustain prey or forage for them. Much of the Sierra's animal diversity and numbers are found from the montane down to the foothill or pinion-sagebrush life zones. The lower in elevation, the more animals you will find.


This stark, cold part of the Sierra is wind-blown and beautiful beneath the deepest blue skies in California—there's no smog up here. This life zone is above the timberline, meaning trees generally cannot survive at this elevation. The plants at California's rooftop are often divided into meadow and rock communities. They must survive in the tiny window of six or seven weeks during the summer when the snow finally disappears.

The alpine soil is rocky and well drained. Since the summers are often sunny and arid, plants must adapt to wind, dry conditions, and rocky soils. Plants do not grow large. Instead, they often grow close to the ground and send down deep taproots.

In the alpine meadows, there are grasses and sedges, such as alpine sedge (Carex subnigricans). The wildflowers also are low-growing species, including primrose monkey-flower (Mimulus primuloides). Few shrubs grow at this elevation, but dwarf huckleberry (Vaccinium nivictum) and a few others can adapt to the various wet places where snowmelt lingers.

Alpine rock plants are among the toughest vegetation in the Sierra. They generally must survive in even rockier soils than the meadow plants. The alpine spring
locoweed (Astragalus kentrophyta) is a good example. The mountain sorrel (Oxyria digyna) is a smaller shrub that can survive in rock crannies.

Very few animals are year-round residents in the alpine zone. The yellow-bellied marmot (Marmota flaviventris) is one of them. There are visitors from lower elevations, and they include the white-tailed jackrabbit (Lepus townsendii) and the Clark's nutcracker (Nucrifraga columbiana).


The highest forests of the Sierra are found here. If you hike up to the timberline anywhere from Kings Canyon National Park up to Lake Tahoe, you will probably see the distorted, heavy trunks of the whitebark pine (Pinus albicaulis) along ridgelines and in windy passes. Other trees near the timberline include the mountain hemlock (Tsuga mertensiana), the foxtail pine (Pinus balfouriana), and the lodgepole pine (Pinus murrayana).

Soils in the subalpine are not usually filled with nutrients, and the winter storms leave 250 to 400 inches of snow annually. With the heavy snowfall, high winds, and low temperatures, trees near the timberline are not very large, nor do they grow very fast.

Many types of shrubs and wildflowers occupy the subalpine as well. This vegetation often can be found in both the upper and lower montane zones as well. Shrubs such as greenleaf manzanita (Arctostaphylos patula) can be found in a wide range of elevations from the subalpine all the way down to the lower montane. The Sierra primrose (Primula suffrutescens) is a wildflower that can usually be found in rocky subalpine areas.

The animal communities are larger in the subalpine areas compared to the alpine zone. Birds, reptiles, amphibians, and mammals live and visit subalpine elevations in the Sierra. There are not a lot of predators at this elevation because prey is more abundant in the montane and foothill areas. The American badger (Taxidea taxus) and the gray fox (Urocyon cinereoargenteus) often hunt for food in the subalpine zone.

Upper and Lower Montane

The heart of the Sierra's conifers is between 3,000 feet and about 8,500 feet in elevation—the upper and lower montane. Biologists separate this part of the forest into elevation belts where certain types of trees dominate the landscape. For instance, the red fir (Abies magnifica) forest occupies the upper montane in well-drained soils between 6,500 and 8,500 feet. The white fir (Abies concolor) ranges from 4,000 to 8,000 feet. The ponderosa pine (Pinus ponderosa) is found from 2,800 feet to about 6,500 feet.

Notice the overlap. The forest belts contain more than a dozen different conifers and many broadleaf trees, and the boundaries are not at all distinct. Four or five different species of conifers, including those from different life zones, can be found in a single stand. You might find both the white and red fir in the same area. One of the more common trees throughout the upper and lower montane is the black oak (Quercus kelloggii), which is found on open, dry ridges from the foothill life zone all the way to 8,000 feet in some areas of the Sierra's western slope. There is not as much variety on the Eastern Sierra, but the mixed conifer forests can be found there between 6,000 and 8,000 feet.

The general rule on the western slope is that the various forest belts extend to higher elevations as you travel south. The phenomenon is largely a function of precipitation and temperature. The Northern Sierra is wetter and cooler than the Southern Sierra because Pacific storms often enter California from the northwest and lose moisture before they reach the Southern Sierra. A shrub that could be found at 3,500 feet in the Northern Sierra can sometimes be found at 5,000 feet or even higher in the Southern Sierra. The same is true for wildflowers. More than 100 miles north of the Southern Sierra, the Fendler's meadow rue (Thalictrum fendleri) can occur all the way down to 3,500 feet. But in the Southern Sierra, it can be found all the way up to 10,000 feet.

The animals in the montane life zones include the larger mammals, such as the mule deer (Odocoileus hemionus), mountain lion (Felix concolor), and black bear (Ursus americanus). Many animals, such as bighorn sheep (Ovis canadensis) will move with the seasons to find food. In winter, the sheep will move down into lower meadows when the snowpack begins to cover their higher elevation feeding grounds.


The foothills of the Sierra can range from 500 feet to 4,000 or even 5,000 feet, based solely on plant species and climate. Other than vegetation and weather, there is no other physical or geological quality that distinguishes this zone from the rest of the range. But foothill vegetation is quite distinctive, including woodland, chaparral, and grassland ecosystems. These plant communities are specially suited to the often dry conditions of foothills, which receive as little as 12 to 15 inches of rainfall a year in the Southern Sierra.

Probably the most dominant woodland tree is the oak, specifically the blue oak (Quercus douglasii). But there are other kinds of oak, including the stately valley oak (Quercus lobata) and interior live oak (Quercus wislizenii). The digger pine (Pinus sabiniana) can be found in many stands of woodland oaks.

Chaparral is found in abundance along the Southern Sierra, but not as much to the north where damper conditions favor the woodlands. Chaparral grows on hot, dry slopes in brush thickets, and there are many plant species in the community. They include common buckbrush (Ceanothus cuneatus) and chaparral pea (Pickeringia montana).

The lower foothills are dominated by grassland species. Bunch grasses are the dominant plants, though the natives have been largely replaced by such exotics as foxtail fescue (Festuca megalura). Grassland wildflower displays in spring are quite extraordinary in heavy rainfall years.

Though the deciduous trees drop their leaves and some other vegetation goes dormant during winter, the foothills come alive in the winter months. Many creatures, including migrating birds, come down from the montane zones to warm up and find food. But many animals, such as the red-tailed hawk (Buteo jamaicensis) and the bobcat (Lynx rufus), live here year-round.


The high desert conditions of the Eastern Sierra create a pinion-sagebrush life zone from 7,000 feet down to about 4,000 feet, which is the elevation of the Owens Valley floor. This life zone is quite different from the western slope foothills because it is far more arid and higher in elevation. Rainfall totals can average as low as 6 inches annually on the valley floor, and perhaps 18 inches at 7,000 feet. Western slope totals are easily twice as high at comparable elevations.

The lower plant communities are filled with Great Basin sagebrush (Artemisia tridentata), which grows well in sandy soil. The Eastern Sierra is known for the sagebrush fragrance that is carried by the wind. But there are many other interesting plants, such as the desert peach (Prunus andersonii).

The upper part of the pinion-sagebrush zone is dominated by the pinion pine (Pinus monophylla) and associated plants, such as mountain mahogany (Cercocarpus betuloides). Quaking aspen (Populus tremuloides) is also found in the higher elevations of the upper pinion-sagebrush zone. The most common streamside tree in this upper area is water birch (Betula occidentalis).

The largest mammals in the pinion-sagebrush zone are deer and bighorn sheep, which eat the shrubs and herbs at these elevations. Many desert animals are found here, too. Birds and small mammals are lighter in color here than elsewhere in the Sierra because the lighter color reduces body heat and provides a better camouflage. These animals include the desert horned lizard (Phrynosoma platyrhnos), sagebrush chipmunk (Eutamias minimus), and pinion jay (Gymnorhinus cyanocephalus).

People in the Sierra

Volcanoes, earthquakes, glaciers, and rivers shaped the Sierra over the last 400 million years. Over the last 10,000 years, Native Americans have been making small, beneficial changes to the landscape. But during the last 150 years, European-American settlers have moved in and made some less than positive and rather astonishing alterations.

The transformations began in the late 1840s when gold mining mania brought a wave of development that resulted in roads, settlements, lumber harvesting, and river damming. Later in the century, thousands of acres were clear-cut by loggers, entire ridges were destroyed by hydraulic miners, and meadows were trampled by grazing livestock. Indeed, gold mining spawned massive commercial and industrial development and a half century of unrestricted resource extraction and ecosystem alteration. Mining, grazing, logging, and transportation came to dominate these mountains.

A conservation backlash followed. In the twentieth century national parks were established, and many thousands of acres were protected. But even with their good intentions, the conservationist thinking—which helped spur the federal government to snuff out as many fires as possible in the Sierra—was not informed enough to avoid another tragic mistake. In removing fire from the forest, the Sierra lost its most effective natural limit on the growth of the forest. People unknowingly created a boon for thick brush, smaller trees, and other vegetation. Now there is enough vegetation, or fuel, to turn many ordinary, natural fires into catastrophic wildfires that could consume thousands of forest acres, choke inland valleys with smoke, and threaten people.

Federal managers and scientists all over the 20 million acres of the Sierra are struggling to figure out the best protections for the range. The job is complicated because 36 percent of the land is in private hands. The rest is held by public agencies, such as the U.S. Forest Service, the Bureau of Land Management, the state of California, the National Park Service, and others. These agencies, private individuals, and commercial interests do not always agree on how to manage the forests.

How differently the pre-nineteenth century inhabitants, the Native Americans, saw the Sierra. Instead of relentless development or rigid preservation, they seemed to understand how to coexist with the ecosystem and maintain it. Evidence of their Sierra lifestyles has been traced back thousands of years in parts of the range. Before the nineteenth century, Native Americans numbered more than 50,000 individuals and spanned the Sierra, ranging from the Tubatulabal in the southern Kern River basin to the Northern Sierra tribes of the Maidu.

The Tubatulabal, Maidu, Yokuts, Miwok, Mono, Paiute, Washoe, and others practiced land management that would sustain plant diversity and maintain their cultural and agricultural pursuits. Their chief tool was fire, which was used to burn meadows, clear vegetation in wooded areas, and disperse seeds. They also transplanted native vegetation and weeded to promote its growth. They pruned, irrigated, and selectively harvested. In many recent discussions with tribal elders about the Sierra, the Native Americans say the range's decline is no mystery: No one is caring for areas the way they did many centuries before Europeans arrived.

Jedediah Smith is believed to be the first person of European background to cross the Sierra during an expedition in 1826 and 1827. He came from the south, trekking along the foothills from the Southern Sierra to the Central Sierra, and he saw many large mammals including vast herds of tule elk (Cervus elaphus nannodes). He eventually crossed west to east at Ebbets Pass in the Central Sierra. Brigades of fur trappers and hunters soon followed, taking elk, bear, deer, antelope, beaver, and other creatures.

Twenty-one years after Smith passed through the Central Sierra, James Marshall found tiny gold nuggets in the South Fork of the American River, just west of present-day El Dorado National Forest. About 500,000 people flooded into California in search of riches. Saw mills sprang up to cut timber for houses and other buildings. About $750 billion of gold was produced over the next several decades. The ecosystem suffered as miners devised hydraulic mining, using strong blasts of water to strip away soils from hillsides and reveal veins of gold.

But as the gold and silver booms ended, loggers became the focus of commercial expansion in the Sierra. The lumber industry provided the timbers, ties, and other products for the Central Pacific and other railroads. California needed lumber to build homes and businesses. However, there were less than 100 lumber mills in the 1850s. By the late 1800s, historians believe the figure had more than tripled and more than a third of the Sierra's forests were taken. Some logging operations removed 70 million board feet annually, decimating the Sierra tree stock in some areas—especially yellow or ponderosa pine (Pinus ponderosa). Many mature giant sequoias (Sequoia giganteum), some 2,000 years old, were cut down in the Southern Sierra. The brittle wood was almost useless in construction, except as fence posts and roof shingles.

At the same time, sheep and cattle grazing affected the foothills, montane, and even subalpine in the Sierra. In the decades between 1860 and 1900, millions of sheep overgrazed Sierra meadows, though no one knows for sure how many animals there were. Because dairy cattle herds needed higher quality rangeland, they were often kept at the lower elevations where they damaged the grasslands.

Government regulation began to grip the Sierra after 1900. In a 40-year period, the U.S. Forest Service, the California Division of Forestry, the National Park Service, and other agencies regulated public lands and had an influence on private land. Dam construction for irrigation and hydroelectric purposes began under the auspices of government regulation, though the agencies and their regulations would become far more restrictive as scientific knowledge evolved during the twentieth century.

By the latter part of the twentieth century, people began to move into the mountains in droves. The population grew from about 300,000 in 1970 to 650,000 in 1990. Almost three-quarters of the people live on the western slope in the foothills. By 2040, projections show the population will grow to about 2 million. Federal officials and scientists are vigorously pursuing plans to protect the range and the people. With all these concerns, officials must plan for a problem nobody faced in 1950: recreation run amok. They must find a way to let millions of people hike, fish, boat, horseback ride, camp, photograph, and see the sights in the Sierra's backcountry playgrounds—yet they must somehow protect these pristine areas as well.

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