California is the only state in the US with an extensive seacoast, high mountains, and deserts. The extreme diversity of the state's landforms is best illustrated by the fact that Mt. Whitney (14,494 ft/4,419 m), the highest point in the contiguous US, is situated no more than 80 mi (129 km) from the lowest point in the entire country, Death Valley (282 ft/86 m, below sea level). The mean elevation of the state is about 2,900 ft (885 m).
California's principal geographic regions are the Sierra Nevada in the east, the Coast Ranges in the west, the Central Valley between them, and the Mojave and Colorado deserts in the southeast. The mountain-walled Central Valley, more than 400 mi (640 km) long and about 50 mi (80 km) wide, is probably the state's most unusual topographic feature. It is drained in the north by the Sacramento River, about 320 mi (515 km) long, and in the south by the San Joaquin River, about 350 mi (560 km). The main channels of the two rivers meet at and empty into the northern arm of San Francisco Bay, flowing through the only significant break in the Coast Ranges, a mountain system that extends more than 1,200 mi (1,900 km) alongside the Pacific. Lesser ranges, including the Siskiyou Mountains in the north and the Tehachapi Mountains in the south, link the two major ranges and constitute the Central Valley's upper and lower limits.
California has 41 mountains exceeding 10,000 ft (3,050 m). After Mt. Whitney, the highest peaks in the state are Mt. Williamson, in the Sierra Nevada, at 14,375 ft (4,382 m) and Mt. Shasta (14,162 ft/4,317 m), an extinct volcano in the Cascades, the northern extension of the Sierra Nevada. Lassen Peak (10,457 ft/3,187 m), also in the Cascades, is a dormant volcano.
Beautiful Yosemite Valley, a narrow gorge in the middle of the High Sierra, is the activity center of Yosemite National Park. The Coast Ranges, with numerous forested spurs and ridges enclosing dozens of longitudinal valleys, vary in height from about 2,000 to 7,000 ft (600–2,100 m).
Melted snow from the Sierra Nevada feeds the state's principal rivers, the Sacramento and San Joaquin. The Coast Ranges are drained by the Klamath, Eel, Russian, Salinas, and other rivers. In the south, most rivers are dry creek beds except during the spring flood season; they either dry up from evaporation in the hot summer sun or disappear beneath the surface, like Death Valley's Amargosa River. The Salton Sea, in the Imperial Valley of the southeast, is the state's largest lake, occupying 374 sq mi (969 sq km). This saline sink was created accidentally in the early 1900s when Colorado River water, via an irrigation canal, flooded a natural depression 235 ft (72 m) below sea level in the Imperial Valley. Lake Tahoe, in the Sierra Nevada at the angle of the California-Nevada border, covers 192 sq mi (497 sq km).
The California coast is indented by two magnificent natural harbors, San Francisco Bay and San Diego Bay, and two smaller bays, Monterey and Humboldt. Two groups of islands lie off the California shore: the Santa Barbara Islands, situated west of Los Angeles and San Diego; and the rocky Farallon Islands, off San Francisco.
The Sierra Nevada and Coast Ranges were formed more than 100 million years ago by the uplifting of the earth's crust. The Central Valley and the Great Basin, including the Mojave Desert and Death Valley, were created by sinkage of the earth's crust; inland seas once filled these depressions but evaporated over eons of time. Subsequent volcanic activity, erosion of land, and movement of glaciers until the last Ice Age subsided some 10,000 years ago and gradually shaped the present topography of California. The San Andreas Fault, extending from north of San Francisco Bay for more than 600 mi (970 km) southeast to the Mojave Desert, is a major active earthquake zone and was responsible for the great San Francisco earthquake of 1906. Damage from that earthquake amounted to $24 million, with an additional $350–500 in fire losses (total losses would amount to about $6 billion in current dollars). More recently, the 1994 earthquake in Northridge caused damage estimated at $13–20 billion, making it the costliest earthquake in US history.
Because water is scarce in the southern part of the state and because an adequate water supply is essential both for agriculture and for industry, more than 1,000 dams and reservoirs have been built in California. By 1993, there were 1,336 reservoirs in the state. Popular reservoirs for recreation are located along the tributaries of the Sacramento and San Joaquim rivers. Clair Lake Eagle, also known as Trinity Lake, is located on the Trinity River. The reservoir has a surface area of 16,400 acres (6,640 ha). Lake Shasta, located on the Sacramento River, has a surface area of 15,800 acres (6,397 ha). Lake Berryessa, located on Putah Creek, has a surface area of 19,250 acres (7,794 ha). Lake New Melones, located on the Stanislaus River, has a surface area of 12,500 acres (5,061 ha). The San Luis Reservoir, fed by the California Aqueduct, has a surface area of 12,500 acres (5,061 ha). Don Pedro Lake, located on the Toulumme River, has a surface area of 13,000 acres (5,263 ha).