Geology And Geophysics

An Overview of the Terrain of California



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California is 45% forest despite being most populous state in the nation. It is also 25% desert, holding some of America's most arid territory. Crowded cities give way to farmland, rangeland, forests, and unpopulated terrain. It has the tallest trees on earth, the Coast Redwoods, Sequoia sempervirens; the most massive, the Giant Sequoias; and the oldest, the Bristlecone Pines, pinus longaeva.




The heart of California is its great Central Valley. A rich agricultural plain, it provides about one third of the food eaten in the United States. It is watered by two rivers, the Sacramento and the San Joaquin, which are dredged deep enough to allow shipping to the inland port cities of Stockton and Sacramento.




The great valley is divided into the San Joaquin and the Sacramento Valleys by the Delta. Here the two great rivers come together and form a mass of islands, each now surrounded by high levees to keep out the rivers that rose as the islands sank, each island troubled by the ceaseless wind that pours through a water gap to the San Francisco Bay. Water supplies for 23 million people are routed through these islands, sent south to Los Angeles, east to Sacramento, or diverted to the thirsty farms and fields of the great valley.




The San Joaquin is the southern half of the central valley. South of it is Tulare, which is classed by geologists as another valley because it has its own drainage. Tulare once held a lake of 570 square miles, but the lake is now farmland growing cotton, rice, and other crops. Merle Haggard wrote a song about working in the fields there as a child: Tulare Dust.




South of Tulare are the sere Tehachapi Mountains. These are part of the transverse ranges, mountains that extend east to west in the southern part of California. Other transverse ranges include the Santa Monica Mountains, the Santa Susanas, and the carved San Gabriels, all draining to the flat alluvial plains that hold Los Angeles and its sprawling suburbs.




Beyond the Tehachapis begins the Mohave Desert. This region receives less than six inches of rainfall a year. Death Valley, in the Mohave, holds the lowest point in North America at Badwater Flat, 282 feet below sea level. The desert also holds the ungainly Joshua Trees, a marker species for this desert. Many animal species, including the Desert Tortoise and the Desert Bighorn, are protected by this National Park, as are mysterious petroglyphs, and ruins of old settlements. This vast region blends into the Colorado
and Sonoran deserts that run east across the southwest U.S.
and south into Mexico.




The Sierra Nevada Mountains run north to south for 400 miles near the eastern border of California. Yosemite is here, a national park that includes a glacier-carved valley surrounded by broken granite domes, hanging subsidiary valleys, waterfalls, and soaring vistas. North of Yosemite, a week-long hike away, is Lake Tahoe, a huge mountain lake shared with the state of Nevada. The Sierras also hold he highest peak in the lower 48 states, Mount Whitney, 14,505 feet tall, and groves of Giant Sequoias, Sequoiandendron giganteum, the most massive trees on earth. The Palisade Glacier, found in the Sierras, is the southern-most glacier in the United States.




East of the Sierras, in their rain shadow, is the territory of basin and range. Here the high desert is formed into long valleys dropped between lifted ranges, in a pattern called horst and graben. Mono
Lake is here, an alkaline lake holding tufa towers formed in the alkaline waters of this ancient lake with no outlet. The White Mountains are also here, with stands of twisted Bristlecone Pines, the oldest trees in the world. The Methuselah Tree, hidden here, is over 4,700 years old.




The northern end of the Central Valley is called the Sacramento Valley, named for its river. North of it are the Klamath Mountains, the southern end of the Cascade Range, and the Modoc Plateau.




The region of the Klamath Mountains extends into Oregon. It is an area of jumbled terrain, an amazing mix of soils, biomes, and cultures. Some of the ground is serpentine soil, hostile to non-native life. The mountains are steep and sometimes jagged, the valleys deep and filled with rushing streams. There are thirty species of conifers here, ranging from huge Coast Redwoods to the rare Foxtail Pines that survive at the treeline where little else can. The last species of tree discovered in America was discovered here. There are rare orchids in narrow boggy valleys, and the eerie cobra lily, which traps insect prey and devours it. There are legends of the Sasquatch, a creature that is a hybrid of bear, ape, and man.




The Modoc Plateau is in the rain shadow of the Klamaths and the Cascades. It's a high lava plateau with a harsh climate. Wildlife includes herds of mule deer, pronghorn antelope, and wild horses. One typical tree is the Modoc Cypress, Cupressus bakeri. It grows slowly on serpentine soils and old lava flows, where it has little competition. Of sparse gray-green foliage, it is well adapted to scarcity. Its cones only open to drop seeds after a forest fire brings the death of the parent tree.




The Cascades, just east of the Klamaths, are part of the Ring of Fire, the chain of volcanoes that encircle the Pacific Ocean. Beautiful Mount Shasta is here, sometimes sighted as a perfect snow-covered cone from the north end of the Sacramento Valley. Mount Lassen is nearby, one of the least visited of the national parks. Both mountains are volcanoes, both believed to be dormant, each with volcanic features like bubbling mud pots and boiling springs.




West and south of the Klamaths stretch the misty Coast Ranges. North of San Francisco the ranges are wrapped in ocean fog and here the hugely tall Coast Redwoods grow best. This land is folded into ridges that run north to south, causing rivers to run far north or south before they turn to reach the sea. Behind the front ranges the land is drier, and here are forests of oak woodland and open grassy areas. South of San Francisco are the Santa Cruz Mountains, with Redwoods where rainfall is high and oak woodland or grassland where it is not. The San Andreas Fault, site of some of California's most destructive earthquakes runs through these mountains. South of them are the Santa Lucias, the mountains of light, dropping abruptly onto the breathtaking vertical coast of Big Sur.





California has offshore islands too, with two groups of note. The Farallon Islands, 27 miles from the Golden Gate and legally part of San Francisco, are a wildlife sanctuary where no humans are allowed except for researchers. They are rocky granitic outcrops alive with birds.




The Channel Islands begin west of Los Angeles and continue south nearly to Mexico. There are eight islands, five of which form a National Park. The U.S. Navy controls two of the islands, San Clemente and lonely San Nicholas. Santa Catalina, the remaining island, is the only one with a population center, the hillside resort town of Avalon, twenty six miles from shore.




California is a place of great contrasts, from its searing deserts to its soaring fog-shrouded redwoods. Lofty Mount Whitney is only 200 miles from the lowest point in Death Valley, and marathon hikers do make the trip between. There are remote islands and resort islands, wild mountain solitude and tidy orchards blooming in spring. Everyone should see California.

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