Physical Geography

In very general terms, most of California consists of two parallel mountain systems—the Sierra Nevada and the Coast Ranges—enclosing a great lowland, the Central Valley. The remainder of the state is largely desert and semidesert, with scattered, low mountain ranges.

The Sierra Nevada extends along or near the California-Nevada border for about 400 miles (640 km). It averages 40 to 80 miles (65 to 130 km) in width and is marked by high peaks and deep canyons. In the highest section, called the High Sierras, are 11 peaks that rise more than 14,000 feet (4,270 m) above sea level. Mount Whitney, at 14,494 feet (4,418 m), is the highest peak in the United States outside Alaska. Yosemite, Sequoia, and Kings Canyon national parks and several national forests and national monuments are in the Sierra Nevada.

The Coast Ranges, up to 50 miles (80 km) wide, include a number of mountain ranges separated by lovely valleys. Altitudes vary from about 2,000 to 9,000 feet (610 to 2,740 m). The mountains are continuous except for a wide gap made by San Francisco Bay, where the rivers of the Central Valley empty into the sea.

In northern California are the moderately rugged Klamath Mountains and the Cascade Range. Except for several volcanic peaks, mountains here crest roughly between 6,500 and 8,500 feet (1,980 arid 2,590 m). Mount Shasta, a snowcapped dormant volcano in the Cascades, rises to more than 14,000 feet (4,270 m), towering majestically over the entire region. Lassen Peak, at the southern end of the Cascade Range, erupted several times early in the 1900's and forms the core of Lassen Volcanic National Park.

The Central Valley is a wide, relatively flat expanse extending some 450 miles (720 km) through the central part of the state. The northern part is often called the Sacramento Valley, the southern part the San Joaquin Valley. Into this great valley flow most of the rivers that begin in the Sierra Nevada and Coast Ranges.

The southern end of the Central Valley is closed off by the Tehachapi Mountains, which stretch between the Sierra Nevada and the Coast Ranges. To the south, the San Gabriel, Santa Ana, and San Bernardino mountains form a barrier between the Pacific shore and the Mojave Desert. The Mojave is a largely barren expanse with numerous dry salt lakes, low mountains, and dry streambeds. Death Valley, site of the lowest point in the Western Hemisphere (282 feet [86 m] below sea level), curves northward from the desert between desolate ranges near the Nevada border. The Sonoran Desert occupies much of the area near the Mexican border.

The land east of the Sierra Nevada and Cascade Range consists of elevated plateaus and basins, forming part of the Great Basin of the western United States. Scattered across this sparsely populated part of the state are low mountain ranges and isolated peaks.

California is subject to frequent earthquakes, particularly in the coastal regions. They are caused primarily by shifting of the earth's crust along fractures known as faults. The San Andreas Fault extends from the Pacific Ocean off Cape Mendocino southeastward through the San Francisco and Los Angeles areas into northern Mexico. Numerous lesser faults occur elsewhere in the state. A few of the quakes have been strong, but most have been of only slight intensity. In 1906 a quake and a fire that followed devastated San Francisco.

The principal rivers within California are the Sacramento and the San Joaquin, which drain the Central Valley and empty into the sea by way of San Francisco Bay. Both rivers are fed by sizable tributaries flowing from adjacent mountains, particularly the Sierra Nevada. Beyond the Central Valley the chief rivers are the Colorado, in the southeast, and the Klamath, in the northwest. Many of the state's smaller rivers are dry during part of the year.

Dozens of lakes, both natural and man-made, are scattered across California. One of the largest, Lake Tahoe, lies in a beautiful setting high in the Sierra Nevada on the border with Nevada. The Salton Sea is a broad, shallow, below-sea-level lake formed when the Colorado River overflowed its banks in the early 1900's. Goose, Honey, Mono, and Clear lakes are also sizable bodies of water.

Much of California is dry, and water resources are distributed unevenly. The wettest area is the north, the driest the south. Extensive canal and aqueduct systems have been constructed to move water southward to meet constantly increasing urban and agricultural use. Among the large carriers are the California Aqueduct, the Los Angeles Aqueduct, and the Colorado River Aqueduct.

California is perhaps more widely known for its climate than for anything else in its natural environment. The climate is often described as being sunny, mild, and dry. Although that is generally true for much of the state, especially the south, there is a considerable range of climatic conditions. Differences are caused mainly by differences in latitude (California spans more than 10 degrees of latitude), by the varying elevation and topography within the state, and by distance from the sea.

Coastal California differs greatly from south to north. The southern one-third is warm and dry; the northern one-third is cool and moist; the central section is transitional. Average January and July temperatures, for example, vary from 55° and 70° F. (13° and 21° C.) at San Diego in the south to 47° and 56° F. (8° and 13° C.) at Eureka in the north. Average annual precipitation at the two cities is 10 and 40 inches (250 and 1,000 mm) respectively. Virtually all the precipitation comes during the rainy season from October through April. The rest of the year is dry. Much fog and mist occurs along the northern half of the coast.

The Central Valley has hotter summers and cooler winters than does most of the coast. It also has greater daily and seasonal temperature ranges. Sacramento, for example, has an average temperature of 45° F. (7° C.) in January and 75° F. (24° C.) in July. Precipitation in the Central Valley decreases from more than 20 inches (500 mm) in the north to roughly 5 inches (125 mm) in the far south. The wet and dry seasons are the same as along the coast.

The climate of the high mountains increases in severity as elevation increases. Many parts of the Sierra Nevada are cold and are blanketed by extremely deep snows. Mountain slopes facing the moisture-bearing winds from the Pacific receive the largest amounts of precipitation.

The plateaus and basins on the drier, leeward sides of the Sierra Nevada and Cascade Range, especially those in the northeast, lie at high elevations and have a continental climate similar to that of most western states. Winters are long and cold; summers are warm to hot.

The low-lying desert area of southeastern California is extremely hot in summer and warm in winter. Temperatures of more than 100° F. (38° C.) frequently occur; the highest temperature ever recorded in North America, 134° F. (57° C.), occurred in this area, in Death Valley, in 1913. Precipitation is scant. Much of the area receives less than 3 inches (80 mm) annually.

The vegetation of California is as varied as the state's climate and land forms. Forests, many of which are under federal administration, cover about two-fifths of the land. The major forest regions are the Sierra Nevada and the northern Coast Ranges. In the Sierras, pine and fir are common; giant sequoia is also found there, mainly in national parks. In the Coast Ranges, redwood, pine, and fir predominate.

The Central Valley, now extensively farmed with the aid of irrigation, was originally a grassland. On the lower slopes of the mountains enclosing the valley grows a mixture of pine, oak, and many other trees, as well as shrubs, grasses, and a profusion of wildflowers. Large areas, especially in southern California, are covered with chaparral (thickets of woody shrubs). In the arid southeast and extreme south is found an assortment of cacti and other desert plants. Unique to the Mojave Desert is the Joshua tree, a tall species of yucca now found mostly in Joshua Tree National Monument.