The Western United States Part 19

In some places the climatic conditions which we should naturally expect seem to be reversed. Oranges are grown in the Great Valley of California as far north as Red Bluff, and actually ripen a month sooner than they do near Los Angeles, five hundred miles farther south. The early ripening of fruits in the Great Valley may be explained by the presence of the inclosing mountain ranges: the Sierra Nevada mountains upon the northeast shut off the cold winds of winter, while the Coast ranges upon the west break the cool summer winds which come from off the Pacific.

Another interesting fact connected with the climate of the West is the influence exerted by the direction of the mountain ranges. As these ranges usually lie across the path of the prevailing winds, their tempering influence is lost much more quickly than it otherwise would be. West of the Coast ranges the summers are cool and the winters are warm. Upon the eastern side of these mountains the winters are somewhat cooler and the summers very much warmer. In the dry, clear air of the desert valleys, far from the ocean, the daily range in temperature is sometimes as great as fifty degrees, while the winters are cool and the summers unbearably hot.

We all know how much cooler a hill-top is than a valley upon a summer day. Where the mountains rise abruptly to a great height, as, for example, does the San Bernardino Range of southern California, one can stand among stunted plants of an arctic climate and look down upon orange orchards where frost rarely forms. Mount Tamalpais, a peak of the Coast Range north of San Francisco, has an elevation of nearly three thousand feet. The summer temperature upon this mountain forms an exception to the general rule, for while the lowlands are buried in chilling fog, the air upon the summit is warm and pleasant.

[Ill.u.s.tration: FIG. 111.--ORANGE ORCHARDS CLOSE UNDER SNOW-CAPPED PEAKS

Highlands, California]

The north and south mountain ranges not only make the interior hotter than it would otherwise be, but rob it of much of the moisture which it should receive. The winter storms coming in from the ocean find the cool mountains lying across their path and quickly part with a large proportion of their moisture. Where the coast mountains are low, as is the case with a great part of California and of Oregon, more of the moisture pa.s.ses on to the next line of mountains, the Sierra Nevada-Cascade Range, the western slope of which is well watered. In the region of the Columbia the Cascade Range is also low, and the storms, which often follow one another in quick succession, sweep across the Columbia plateau and over the Rocky Mountains. Farther south, not only are the storms fewer in number, but the mountains are very much higher, so that the desert basins of the lower Colorado and Death Valley region are extremely dry.

One can in imagination stand upon the summit of the Sierra Nevada mountains, and upon the one hand look down upon barren valleys of vast extent, broken by mountains almost as barren, where nothing can be grown except by means of irrigation; and upon the other side, toward the coast, see a country plentifully visited by rain, and either covered with forests or given over to farming and fruit-raising.

The Rocky Mountains form the eastern barrier which the storms encounter.

Their summits are very high and are covered with deep snow during the winter. East of these mountains lie the Great Plains, where the precipitation is light until we go far enough toward the Mississippi Valley to reach the influence of the moist air currents from the Gulf of Mexico. Many storms originate over the region of the Gulf of California, particularly in the late summer, and supplement to some extent the light winter storms of Arizona and New Mexico.

The storms of which we have been speaking are known as cyclones.

This term does not refer to the local storms which occur in the Mississippi Valley and are frequently so destructive, but to great disturbances of the air. Sometimes the column of whirling air is more than a thousand miles in diameter. The air in a cyclone is circling and at the same time rising, so that the motion is spiral.

If you will study an eddy in a stream of water, you will get an idea of the nature of the motion, except that in the case of the water eddy the movement is downward. The motion of the particles in the dust-whirls which all have seen moving across the fields near noon on warm summer days ill.u.s.trate the movement of the air in one of these great storms. The direction of the air in a cyclone is opposite to that of the hands of a clock.

When the wind comes up from a southerly point, when high, thin clouds, gradually growing thicken, spread over the sky, and the barometer begins to fall, then it is known that a storm is corning.

If one will learn to watch the clouds and the winds carefully he may become able to predict a storm with almost as much certainty as if he had a barometer. This instrument registers the pressure of the air, which is always less within the area of a storm, because then the air is rising. So when the barometer falls we may always know that a storm is approaching.

The greater number of the storms which occur in the central and northern United States come in from the Pacific Ocean in the lat.i.tude of Was.h.i.+ngton. Continuing east or southeast they reach the Mississippi Valley, and then turn northeastward toward the St. Lawrence Valley.

In the summer months there are few storms, and they very rarely reach as far south as California. As winter approaches the storms become more frequent and severe, and move farther and farther south until the whole land as far as Mexico receives a wetting.

Upon the Pacific coast there is often very little warning of the coming of a storm, but in the Middle and Eastern States they may frequently be predicted several days in advance. With the pa.s.sing of one of these storms the temperature falls rapidly, and this lowering of temperature, together with the fierce wind, gives rise upon the Great Plains to "blizzards" or "northers." These storms endanger the lives of both men and animals.

At different times in the year, particularly in winter, spring, and early summer, warm, dry winds occur. Those winds which sweep down from the heights of the Rocky Mountains and quickly melt the snows are known as "chinooks." The hot north and east winds of California often do great damage to growing crops.

Now let us sum up briefly the factors which have together produced the climatic features of the Pacific slope.

(1) Ordinarily the factor of the greatest importance is lat.i.tude.

We should expect that Seattle would have a much colder climate than San Diego because it receives the sun's rays more slantingly.

(2) The influence of lat.i.tude is greatly modified by the temperate winds blowing from the Pacific, so that places far separated in lat.i.tude differ but little in average temperature, their summers being cooler and their winters warmer than we should expect them to be.

(3) The storms pa.s.s over the land with the general easterly movement of the air. The largest number pa.s.s east across the northern portion of the United States. The farther south we go the fewer are the storms and the less the rainfall. Along the coast of Was.h.i.+ngton the annual rainfall is nearly one hundred inches. At San Diego it is only about ten inches.

(4) The position of the mountain ranges causes the influence of the ocean on the air to be lost within a short distance toward the interior of the continent, so that the extremes of temperature rapidly become greater. The position of the mountains also affects the rainfall of the interior. Since a large proportion of the moisture is condensed upon their ocean slopes, the climate of each succeeding range toward the interior becomes more dry and desert-like. While in some of the lowlands thus cut off from the ocean the climate is extremely arid, yet the country is relieved from utter barrenness through the presence of mountain peaks and ranges, which often condense considerable moisture.

[Ill.u.s.tration: FIG. 112.--SCENE IN FORESTS OF WAs.h.i.+NGTON

Showing spruce and cedar]

(5) The higher a region is above the sea, the colder the climate.

The summit of a high mountain and the valley at its base may be in the same lat.i.tude, and yet one may possess an arctic climate while the other has a sub-tropical one.

The heavy rainfall in western Was.h.i.+ngton, Oregon, and northern California results in dense forests. To the south, the rainfall upon the lowlands is not sufficient to produce forests, but as it is greater upon the mountains, trees thrive upon their sides.

The elevation at which trees will grow becomes higher and higher as we go into the more desert regions, until in northern Arizona it is found to be above six thousand feet. The high plateaus are generally treeless, but are covered with such shrubs as greasewood and sage-brush.

We see now that our climate is the product of many factors. It frequently varies greatly in places only a few miles distant from each other. Consequently there may be a great variety of productions and industries in one small area, while in other regions the climate and productions are almost unchanged for hundreds of miles.

SOMETHING ABOUT IRRIGATION

Travellers from the Eastern States who visit New Mexico for the first time are attracted by many unusual sights. There are the interesting little donkeys, the low adobe houses of the native Mexicans, and the water ditches winding through the gardens and fields, which are divided into squares by low ridges of earth.

If the fields are seen in the winter time, when dry and barren, the meaning of their checkered appearance is not at first clear, but in the spring and summer one is not long in finding out all about them. When the time comes to sow the seed, water is turned into these squares from the ditches which traverse the valleys, and one square at a time is filled until the ground in each is thoroughly soaked. Afterward, when the ground has dried enough to be easily worked, the crop is put in. The seeds soon sprout under the influence of the warm sun, and the land becomes green with growing plants. The same method of moistening the ground is used for the orchards and vineyards.

What is the use of all this work? Why not wait for the rains to come and wet the earth, as the farmer does in the eastern United States? The Mexicans, who have tilled these valleys for more than two hundred years, ought certainly to have learned in all that time how to get the best returns. You may be sure that they would not water the ground in this way if it were not necessary. The fact is that over a large portion of the western half of the United States it does not rain enough to enable the farmer to grow his crops. The climate is generally very different from that of the Middle and Eastern States.

When the Mexicans moved northward into the valley of the Rio Grande River, into Arizona and California, they found a climate similar in many respects to that at home, and soon learned that it was necessary to water the land artificially in order to make it productive. Though in many places sufficient rain fell, yet the heaviest rainfall came in the late summer or winter, when the plants needed it less, while the spring and summer were long and dry. The Mexicans were not the first to practise watering the land, if we may judge from the ruins of ancient ditches constructed by the primitive Indian inhabitants. It is evident that they too made use of water in this manner for the growing of their corn and squashes.

This turning of water upon the land to make it productive is termed "irrigation." The work is performed in different ways, as we shall see later. Irrigation is now carried on through all portions of the United States where the rainfall is light and streams of water are available.

To one who has lived in a country where there is plenty of rain, it seems to involve a great deal of work to prepare the land and to conduct water to it. One may feel pity for the farmer who has to support himself in this manner in so barren a country. I am sure, however, that if any such person will stop to think, he will remember times when in his own fertile home the expected rain did not come, and the vegetation wilted and dried up. He may have become discouraged because of a number of "dry years," but probably never thought that he had the means at hand to make up, at least in part, for the shortcomings of Nature, in sending too much rain one year, and another year too little.

[Ill.u.s.tration: FIG. 113.--WATER-WHEEL FOR LIFTING WATER FOR IRRIGATION, VIRGIN RIVER, SOUTHERN UTAH]

It would doubtless have paid such a farmer many fold to have been prepared at the coming of a dry year to turn the water from a neighboring stream over his lands. This process would have involved a good deal of labor; but how the plants would have rejoiced, and how abundantly they would have repaid him for the extra trouble!

The showers come without regard to the time when growing things need them most, but with irrigation the crops are independent of the weather. The farmer may be sure that, if he prepares the ground properly and sows the seed, the returns will be all that he can wish. In many localities several crops may be raised in a year by this method where otherwise only one would grow.

Now let us see how the water is taken from the streams and what are the different methods employed to distribute it over the land.

Almost every valley is traversed by a stream, great or small. It may be a river, with a large volume of water, or a creek which completely dries up during the long, rainless summers of the West.

[Ill.u.s.tration: FIG. 114.--GARDEN IRRIGATION, LAS CRUCES, NEW MEXICO]

In rare cases the stream may flow upon a built-up channel which is as high as the valley, but usually it is sunken below the level of the floor of the valley, and enclosed by banks of greater or less height. How is the water to be sent over the land? Where the current is swift you may sometimes see a slowly turning water-wheel, having at the ends of the spokes little cups, which dip up the water as the wheel revolves and pour it into a flume that runs back over the land. At some places engines are used to pump the water from the stream and lift it to the desired height.

[Ill.u.s.tration: FIG. 115.--IRRIGATING AN ALFALFA FIELD, ARIZONA]

Generally, however, another method is employed: the water is taken out of the stream in an artificial channel dug in the earth. But in order to get the water at a sufficient height to make it flow over the fields, it is necessary to start a ditch or ca.n.a.l at a favorable point some distance up the stream, perhaps miles from the garden.

The ditch is made with a slope just sufficient for the water to flow. The slope must be less than that of the river from which the water is taken, so as to carry the stream, at last, high enough to cover the lands to be irrigated.

Visit almost any valley in the West where agriculture or fruit-growing is being carried on, and you will at once notice the lines of the ditches, apparently level, as they wind around the hillsides. At convenient distances there are gates to let out the water for the orchards and fields.

The ground may be moistened in different ways. The first method is that employed by the Mexicans, who, if we except the Cliff Dwellers, were the first to introduce irrigation into our country. This consists in dividing the land into squares by embankments and allowing the water to flood each in succession. The method is known as irrigation by checks, and can be used conveniently only upon nearly level land.

In many orchards a series of shallow furrows is ploughed between the rows of trees, and the water is allowed to flow down these until the soil is thoroughly soaked. In alfalfa fields the water is often turned upon the upper end and permitted to work its way across until it reaches the lower edge, soaking the ground as it goes. The slopes must in every case be so gentle that the current will not be strong enough to carry away the soil.

Once in every two to four weeks throughout the spring and summer, the exact period depending upon the rapidity with which the ground dries, the wetting is repeated. If the soil is light the water must be turned on more often and a larger supply is required.

It frequently happens that the stream from which the water is taken so nearly dries up in the summer, when the water is most needed, that the cultivated lands suffer severely. During the winter little if any irrigation is necessary, but at that time the streams are so full that they frequently run over their banks and do great damage.

How to preserve the water thus going to waste and have it at hand for summer use has been an important problem in regions where every particle of water is valuable. Study of the question has led to the examination of the streams with reference to the building of reservoirs to hold back the flood waters. A reservoir may be formed of a natural lake in the mountains in which the stream rises, by placing a dam across its outlet and so making it hold more water.