The valleys parallel with the coast range, as well as those which extend eastwardly in all directions among the hills towards the great plain of the Sacramento, are of unsurpassed fertility. Their soil is a deep, black alluvian, and so porous that it remains perfectly unbroken by gullies, notwithstanding the great quantity of water which falls into it during the wet season. The productiveness of "California," says Frémont in his Memoir on that region, published in 1848, "is greatly modified by the structure of the country, and under this aspect may be considered in three divisions—the southern, below Point Concepcion and the Santa Barbara mountain, about latitude 35°; the northern, from Cape Mendocino, latitude 41°, to the Oregon boundary; and the middle, including the bay and basin of San Francisco and the coast between Point Concepcion and Cape Mendocino. Of these three divisions the rainy season is longest and heaviest in the north, and lightest in the south. Vegetation is governed accordingly—coming with the rains—decaying where they fail. Summer and winter, in our sense of the terms, are not applicable to this part of the country. It is not heat and cold, but wet and dry, which mark the seasons, and the winter months, instead of killing vegetation, revive it. The dry season makes a period of consecutive drought, the only winter in the vegetation of this country, which can hardly be said at any time to cease. In forests, where the soil is sheltered, in low lands of streams and hilly country, where the ground remains moist, grass continues constantly green and flowers bloom in all months of the year.
"In the southern half of the country the long summer drought has rendered irrigation necessary, and the experience of the missions, in their prosperous day, has shown that, in California, as elsewhere, the dryest plains are made productive, and the heaviest crops yielded by that mode of cultivation. With irrigation a succession of crops may be produced throughout the year."
The peculiarities of the climate of California are so well explained in a letter from the Honorable T. Butler King, that we extract his observations thereon as the most valuable portion of the report made by him to the United States Government in March, 1850.[82]
"The north-east winds, in their progress across the continent, towards the Pacific ocean, pass over the snow-capped ridges of the Rocky Mountains and the Sierra Nevada, and are of course deprived of all the moisture which can be extracted from them by the low temperature of that region of eternal snow; consequently no moisture can be precipitated from them, in the form of dew or rain, in a higher temperature than that to which they have been subjected. They pass therefore over the hills and plains of California, where the temperature is very high in summer, in a very dry state; and so far from being charged with moisture, they absorb, like a sponge, all that the atmosphere and surface of the earth can yield, until both become, apparently, perfectly dry.
"This process commences when the line of the sun's greatest attraction comes north in summer, bringing with it vast atmospheric movements. Their approach produces the dry season in California, which, governed by these laws, continues until some time after the sun repasses the equator in September, when, about the middle of November, the climate being relieved from these north-east currents of air, the south-west winds set in from the ocean, charged with moisture—the rains commence, and continue to fall, not constantly, as some persons have represented, but with sufficient frequency to designate the period of their continuance, as the wet season, from about the middle of November until the middle of May, in the latitude of San Francisco.
"It follows, as a matter of course, that the dry season commences first, and continues longest in the southern portions of the Territory, and that the climate of the northern part is influenced in a much less degree by the causes which I have mentioned than any other section of the country. Consequently, we find that as low down as latitude 39° rains are sufficiently frequent in summer to render irrigation quite unnecessary to the perfect maturity of any crop which is suited to the soil and climate.
"There is an extensive ocean current of cold water, which coming from the northern regions of the Pacific, or, perhaps, from the Arctic, flows along the coast of California. It arrives charged with, and in its progress, emits air, which appears in the form of fog when it comes in contact with a higher temperature of the American coast, as the Gulf-stream of the Atlantic exhales vapor when it meets, in any part of its progress, a lower temperature. This current has not been surveyed, and, therefore, its source, temperature, velocity, width, and course, have not been accurately ascertained.
"It is believed by Lieut. Maury, on what he considers sufficient evidence—and no higher authority can be cited—that this current comes from the coasts of China and Japan, flows northwardly to the peninsula of Kamptschatka, and, making a circuit to the eastward, strikes the American coast in about latitude 41° or 42°. It passes thence, southwardly, and finally loses itself in the tropics. * *
"As the summer advances in California, the moisture in the atmosphere and the earth, to a considerable depth, soon becomes exhausted; and the radiation of heat, from the extensive naked plains and hill-sides, is very great.
"The cold, dry currents of air from the north-east, after passing the Rocky Mountains and the Sierra Nevada, descend to the Pacific and absorb the moisture of the atmosphere to a great distance from the land. The cold air from the mountains, and that which accompanies the great ocean current from the north-west, thus become united, and vast banks of fog are generated, which, when driven by the wind, has a penetrating or cutting effect on the human skin, much more uncomfortable than would be felt in the humid atmosphere of the Atlantic at a much lower temperature.