California is stretched on 1.250 kilometers, a little more than the distance from Rotterdam to Rome. Bordered in north by Oregon, the east by Nevada and Arizona and in the south by Mexico, with 404.800 km2, it is the third American State for the surface after Alaska and Texas. In the west, the coast, of which developed reached 2.000 km, plunges in the Pacific Ocean.

California is a state of mountains. With the north-western angle is the solid mass of Klamath, bordered in the east by the chain of the southernmost Cascades. The Nevada Sierra prolongs the Cascades towards the south, is curved towards the west while decreasing by altitude and comes to be joined, with the collar of Tejon Pass, a series of chains directed of is in west, the Transverse Arrange. Coast Arrange, parallel with the ocean, only stopped by bay of San Francisco and some estuaries, close the loop, of the Transverse in Klamath. To the south of the Transverse, as a prolongation of Coast Arrange, Peninsular Ranges slip by to the point of Baja California. Is State is occupied by the province of the Basin & Range, where alternate desert chains and basins.

Peninsular, Transverse and Coast Ranges leave only one weak place to the coastal plains and, very often, fall right into the ocean. San Diego, Los Angeles, Monterey, San Francisco, installed close to the rare natural ports, extended on the bordering hills. Other agglomerations, much smaller, occupy estuaries, alluvial plains and the rare bands of ground available between sea and mountains.

Inside the long rectangle defined by the Sierra Nevada, the Transverses, Coast Arrange and the Cascades is the Central, long 720 km and broad Valley from 65 to 100. It accommodates the valleys of San Joaquin, in the south, and of Sacramento, in north, which run one towards the other with the length of the same line and meet to feed bay of San Francisco. Basin of filled up collapse of sediments, the Central Valley does not exceed 150 meters of altitude and goes down by places to the sea level. Its flatness, famous in the geographers, is a benefit for the farmers: Central Valley is the object of an intensive farm, very diversified, where citrus fruits, fruits, vine, rices, cereals and breeding are côtoient. The secondary cities, Fresno, Stockton and Bakersfield, are there.

With, on average, a thousand of meters of altitude, Coast Ranges consist of three to four chains separated by valleys. Parallels with the ocean, they make barrier with the wind and, as one moves away towards the east, precipitations decrease: the Central Valley receives only very little water. Coastal rivers and rivers run parallel with the chains, until they clear a passage towards the Central Valley or the Pacific.

The major part of precipitations takes place along the coast and on the Western slope of the Nevada Sierra, whose rivers run of is in west and dissect the mountain of deep canyons. Largest feed Sacramento, in the north of San Francisco. In the south, badly drained by San Joaquin, the plain was formerly an immense marsh, from which many ponds were drained in summer. An important canal system, built end of XIXme at the beginning of XXme century, made it possible to do of them one of the agricultural areas most productive of the United States.

To the east of the State extend from the desert or semi-desert areas, very dissimilar according to the latitude. In the north, wedged between the chain of the Cascades and the first mountains of the Basin and Arranges, the volcanic grounds of the Plate of Modocs, irrigated small rivers and constellated with lakes, remains sufficiently sprinkled to allow the breeding and the associated cultures. In the south, between Peninsular and Arizona, the desert of Colorado, in the prolongation of the Gulf of California, occupies Imperial and Coachella Valley. This “Low Desert” is a hot desert: altitude is there regularly with the lower part of the sea level, and the bottom of Salton Sea, a salt water big lake, is with - 84 meters. An almost permanent sun and the water of Rock, drawn from Colorado, transformed this desert into garden. In north, Coachella Valley shelters several average agglomerations, such as Palm Springs and Indio, where the pensioners come to seek heat and light, far from the tumult of Los Angeles.

In the north and the west of these valleys, the Mojave desert, of larger altitude (High Serves), almost unoccupied, is prolonged until in the Valley of Death. With the foot of the Nevada Sierra, in the east, the valley of Owens lengthens on 180 km. Since 1913, its water feeds Los Angeles with the detriment of the bordering farmers: without it, L.A. would have remained a small town. These arid zones belong to the area of the Basin & Range and, in the north of Mono Lake, the province of the Large Basin.

Even if some come from a relatively old base, all these reliefs are young: the tectonic movements are the cause and continue to modify them. A network of faults allows the permanent adjustment of the grounds these movements. It is the seat of ceaseless earthquakes whose great majority is unperceivable; most important, two or three times per century, have disastrous consequences. Most famous of these faults is that of San Andreas.

A cold current, from Alaska, maintains along the coast a moderate climate. Above the grounds, the ascending currents aspire the sea air, whose moisture condenses and forms tough fogs. The summer, it is all the basin of the Central Valley which is used as vacuum cleaner: the more the weather is hot in the valley and the more durable the fogs are strong and. This permanent moisture allows the existence, of the south of Monterey to Oregon, a species of sequoia, the redwoods, of which highest 120 meters reach.

Seventy percent of the population gather in five great agglomerations: Los Angeles, San Diego, Monterey, San Francisco, Sacramento. More than twenty percent live on the coast between San Diego and Monterey, and in the southernmost part of Valley Exchange. North, with a more rigorous climate and little of industrial activity, is depopulated. The population of the deserts, Coachella Valley put aside, is very weak.

These strong differences in a point to another in altitude, moisture, the duration of the seasons, the nature of the grounds cut out California in very different compartments, and one passes in a few tens of kilometers of the arid valley of Owens to the snow-covered peaks of the Nevada Sierra, of the choking heat of Valley Exchange to the tough fogs of the coast, of the gullied sides of Coast Ranges to the punt valley of Salinas and its cultures.