The heartland of California is the Central Valley, which runs for 450 miles (725 km) through the centre of the state, forming a trough between the Coast Ranges to the west and the Sierra Nevada to the east. The valley is the state’s agricultural centre. Its single opening is the delta through which the Sacramento and San Joaquin rivers drain into San Francisco Bay. The valley is sealed off by the Cascade Range to the northeast and by the Klamath Mountains to the northwest. In the far north the terrain is rugged and heavily forested, becoming wetter on the coastal side and drier and barren in the higher northeast. In the south the Central Valley is closed off by the transverse ranges, most notably the Tehachapi Mountains, which are regarded as a dividing wall between southern and central California.

Most of eastern California is desert. The sparsely settled northeastern corner of the state is a jumble of barren plains and mountains, as well as a volcanic plateau. In the east-central region is the Trans-Sierra desert, which extends along the sheer east escarpment of the Sierra Nevada range and comprises part of the vast interstate Great Basin of the Basin and Range Province. The Trans-Sierra desert ranges from 2,000 to 7,400 feet (600 to 2,300 metres) above sea level. Its largest towns are in the Owens Valley, which was a fertile farmland until its groundwater flow was diverted to Los Angeles through a mammoth series of conduits built in 1908–13.

The Sierra Nevada rises just to the west of the Trans-Sierra desert. The eastern slope of the Sierra Nevada is sheer, dropping some 10,000 feet (3,000 metres) within a 10-mile (16-km) stretch near Owens Lake. On the west the range slopes in gradually declining foothills toward the Central Valley, comprising the San Joaquin and Sacramento river valleys. From the wall that rises near Lassen Peak in the north, the Sierra Nevada extends south for 430 miles (700 km) to the fringes of Los Angeles. Aside from Mount Whitney (14,494 feet [4,418 metres] above sea level), 10 other peaks in the Sierra Nevada exceed 14,000 feet (4,200 metres) in elevation. East-west passes are few but high; some are found at more than 9,000 feet (2,700 metres) in elevation. There are three national parks in the Sierra Nevada: Kings Canyon, Sequoia, and Yosemite. The last, which was designated a UNESCO World Heritage site in 1978, rises from the purplish foothills of the Mother Lode Country and extends through the ice-carved valleys of the Merced and Tuolumne rivers. Its valleys feature waterfalls and granite domes.

In the southeast lies the Mojave Desert, which, at more than 25,000 square miles (65,000 square km), occupies one-sixth of the land area of California. Its landmarks are broad basins and eroded mountains, fault blocks, and alluvial surfaces, most of which are more than 2,000 feet (600 metres) above sea level. Vegetation includes the evergreen creosote bush, yucca, saltbush, burroweed, encelia, cottonwood, and mesquite. Higher up are juniper and piñon pine.

Just south of the Mojave Desert is the lower Colorado Desert, an extension of the Sonoran Desert, which begins in the Coachella Valley. The Colorado Desert descends to the Imperial Valley adjacent to the Mexican border. The valley is a heavily irrigated agricultural area known for its winter crops. More than 4,000 square miles (10,500 square km) of the desert lie below sea level, including the 300-square-mile (800-square-km) Salton Sea, a lake with no outlet that was created in 1905–07 when the nearby Colorado River broke out of its channel.

The roughly 1,100-mile- (1,800-km-) long coastline of California is mountainous, most dramatically so in the Santa Lucia Range south of San Francisco, where towering cliffs rise about 800 feet (240 metres) above the ocean. Hills of lesser elevation flank entrances to the coast’s three major natural harbours, at San Diego, San Francisco, and Eureka. Coastal mountains, made up of many indistinct chains, are from about 20 to 40 miles (30 to 65 km) in width and from 2,000 to 8,000 feet (600 to 2,400 metres) in elevation.

Southern California’s dense settlement lies along a coastal plateau and in valleys ranging from about 10 to 60 miles (16 to 100 km) inland. Along the coast north of the Tehachapi Mountains, the population becomes sparser, though the central coastal region has grown rapidly since the 1990s. The populous coastal area around San Francisco Bay gives way to the less-developed northern coast, where lumbering and fishing villages lie beside creeks and rivers flowing from the Coast Ranges. This is the area of coastal redwood forests and Redwood National Park, which was designated a UNESCO World Heritage site in 1980.

The 800-mile (1,300-km) San Andreas Fault is a major fault line running through most of California. Tectonic movement along the fault has caused massive earthquakes, including the San Francisco earthquake of 1906. The Hayward Fault in the San Francisco Bay Area and the San Gabriel fault zone in metropolitan Los Angeles have produced several major earthquakes, though the destructive quake centred in the Los Angeles suburb of Northridge in 1994 occurred along one of the San Andreas’s larger secondary faults. Separate fault systems in the Sierra Nevada and the Klamath Mountains are tectonically active as well.

Water is chronically scarce in southern California and the desert regions, but excesses of rain and snowmelt cause winter flooding along the rivers of the northern coast. Complex systems of dams and aqueducts transport water from north to south, but not without the protests of those who regard the export of water from their regions as a bar to future growth or as a threat to environmental balance. The Colorado River Aqueduct at the Arizona border carries water from that river across the southern California desert and mountains to serve the Los Angeles metropolitan area. The California State Water Project, launched in 1960, is the largest water-transfer system ever undertaken. It is designed to deliver water daily from the Feather River (a tributary of the Sacramento River) in north-central California to communities as far south as the Mexican border.

The largest lake of the Sierra Nevada is Lake Tahoe, astride the California-Nevada border at an elevation of 6,229 feet (1,899 metres). A mountain-ringed alpine lake about 193 square miles (500 square km) in area, it has among the world’s greatest average depth and a maximum depth of about 1,640 feet (500 metres). Elsewhere in the Sierra lie hundreds of smaller lakes, some above the timberline in regions of tumbled granite and smooth-walled canyons. West of the Sierra Nevada is Clear Lake; at 67 square miles (174 square km), it is the largest natural lake wholly within the state. On the eastern flank of the Sierra are Mono Lake and Owens Lake, both long endangered by agricultural development.