The influence of temperature upon precipitation, and the limits which it throws about arboreal vegetation, are here most forcibly illustrated. In Shasta valley, at an elevation of about 3,000 feet above the sea, where the average temperature is high as compared with that upon the mountain itself, the precipitation is always in the form of rain, but not sufficient in quantity, especially on account of its unequal distribution throughout the year, to support more than a scanty growth of stunted trees. In the autumn storm clouds gather about the summit, and showers become frequent, spreading over the land in copious rains. Before the spring eight ninths of all the annual rain has fallen and the country is brilliant with living green. As summer advances the refreshing showers disappear and the cloudless sky affords no protection from the burning sun; the bright green fades away and the earth gradually assumes that uninviting seared aspect which pervades all nature in the season of drought. Upon the lower slopes of the mountain, by its cooling influence upon the atmosphere, the rainfall is greatly increased, and the vegetation is luxuriant. The vegetation is almost wholly coniferous. Among nearly a score of species the sugar-pine is monarch, frequently attaining a diameter of twelve and a height of over two hundred feet. Farther up the mountain these gradually give way to the firs, whose tall, graceful forms are in perfect keeping with the majestic mountain behind them. Their black and yellow spotted trunks and branches, draped in long pendant moss, present a weird, almost dismal aspect, making a fit promenade for the mythical deities supposed by the aborigines to inhabit the mountains. To assume that in the timber belt the slopes of the mountain are everywhere covered with majestic trees, would certainly be wide of the truth, for within the forests are large treeless tracts, sometimes hundreds of acres in extent. From a distance these green, velvety acres appear to be very inviting pastures, and present the most desirable path of ascent. A closer examination, however, discovers to the observer that instead of grass these green fields are clothed in such a dense shrubbery of manzanita, ceanothus, and other bushy plants, as to be almost impassable. One attempt to cross a patch of chaparral, or “Devil’s acre,” as it is sometimes appropriately called in western vernacular, will convince the traveler that his best path lies in the forest.
As the timber gradually dwindles away from the foot of the mountain to almost nothing in Shasta valley, so also it diminishes in stature, from an altitude of 7,000 feet upwards to the snow region, where the precipitation is generally, if not always, in a solid form of snow in winter and sleet in summer.
Of the tree-like vegetation, one of the pines reaches farthest up the slopes. Its stem grows shorter and the top flattens until, at an elevation of about 9,000 feet, the branches are spread upon the ground, so that not unfrequently the pedestrian finds his best path upon the tree-tops. Beyond these, on the snowless slopes, are found only scattered blades of grass, and the welcome little hulsea, the edelweiss of our Alpine regions, with its bright flowers to alleviate the arctic desolation of the place. The red and yellow lichens cling to the rocks and the tiny prolococcus flourishes in the snow, so that one is frequently surprised, upon looking back, to see his bloody footsteps.
In the Alps, between the forests and the snow, are often found extensive pastures where the herds which furnish milk for the celebrated Swiss cheese are grazed during the milder seasons of the year. In northern California similar pastures do not occur about the snow-capped summits, probably on account of the unequal distribution of the annual rainfall.
To those who are fond of novelty, the greatest interest of the upper portion of Mt. Shasta attaches to its glaciers. They are five in number, and all are found side by side upon its northern half, forming an almost continuous covering above 10,000 feet for that portion of the mountain point. Upon the northern and western slope of the mountain is the Whitney glacier, with its prominent terminal moraines. Next to the eastward is the Bulam glacier, with the large pile of debris at the lower end. Then comes the broad Hottums glacier and the Wintum. The Konwakitong, which is the smallest of the group, lies upon the southeast side of the mountain. Whitney glacier is more like those of the Alps than any other one of the group. Its snow-field lies upon the northwestern slope of the mountains, from whence the icy mass moves down a shallow depression between Shasta and Shastina. Mr. Ricksecker, who has made a careful topographical survey of the mountain, has measured the dimensions of all its glaciers. The limits of the Whitney glacier are well defined; its width varies from 1,000 to 2,000 feet, with a length of about two and one-fifth miles, reaching from the summit of the mountain down to an altitude of 9,500 feet above the sea. It is but little more than a decade since the first glaciers were discovered within the United States, and we should not be disappointed to learn that the largest of them, about the culminating point of the Cascade Range, would appear Liliputian beside the great glacier of the Bernese Oberland, and yet the former are as truly glaciers as the latter. In the upper portion of its course, passing over prominent irregularities in its bed, the Whitney glacier becomes deeply fractured, producing the extremely jagged surface, corresponding to the surfaces of the Alpine glaciers. Lower down the crevasses develop, and these, with the great fissure which separates it from the steep slopes of Shastina, attest the motion of the icy mass. They frequently open and become yawning chasms, reaching 100 feet into the clear, green ice beneath. Near its middle, upon the eastern margin, the Whitney glacier receives large contributions of sand, gravel and bowlders, from the vertical cliffs around which it turns to move in a more northerly direction. In this way a prominent lateral moraine is developed. From the very steep slopes of Shastina, upon the western side, the glacier receives additions in the form of avalanches. Here the snow clings to its rocky bed until the strain resulting from accumulation is great enough to break it from its moorings and precipitate it upon the glacier below. The most striking feature of the Whitney glacier, and that which is of greatest interest from a geological point of view, is its terminal moraine, which appears to be fully a mile in length. Its apparent length is much greater than the real, from the fact that the glacial ice extends far down beneath the covering of detritus. It is so huge a pile of light colored debris, just above the timber line, that it is plainly visible from afar off.
In comparing the morainal material about Mt. Shasta with that of Alpine glaciers, a feature that is particularly noticeable is the smallness of the bowlders. Upon Alpine glaciers they frequently have a diameter greater than ten feet, but about the Whitney and other glaciers of Mt. Shasta they are rarely as much as three feet in diameter. This is readily explained by the fact that the glaciers of Mt. Shasta do not move in deep valleys bounded by long, deep slopes, with many high cliffs which afford an opportunity for the formation of large bowlders. Although the Whitney glacier has its boundaries more clearly defined than any of the other glaciers about Mt. Shasta by the depression in which it moves, the valley is very shallow, and one looks in vain along its slopes for traces of polished rocks like those so magnificently displayed on the way from Meiningen to Grimsel, in the valley of the Aar. Below the terminal moraine the milky water of Whitney creek wends its way down the northern slope, plunges over a fall hundreds of feet high, into a deep cañon, and near the base of the mountain is swallowed up by the thirsty air and earth. The presence of marginal crevasses, lateral and terminal moraines, and the characteristic milky stream which issues from the lower end, are proofs that the Whitney glacier still moves, but the rate of motion has not yet been determined. The row of stakes planted last July were covered with snow before the party could reach them again in the latter part of October.
Upon the northwestern slope of the mountain, besides the Whitney glacier, there is the Bulam, differing chiefly in that it is contained in a broader, less definite valley, and forming an intermediate step toward the Hottum glacier, which is one of the most important and remarkable of the group. Unlike ordinary glaciers, it has no valley in which it is confined, but lies upon the convex surface of the mountain. Its upper surface, instead of being concave anywhere, is convex throughout from side to side, and its width (123 miles) is almost as great as its length (162 miles). At several places the surface of the glacier is made very rough by the inequalities of its bed. This is especially true of its southern portion, where prominent cliffs form the only medial moraine discovered upon Mt. Shasta. Throughout the greater part of its expanse the glacier is deeply crevassed, exposing the green ice occasionally to the depth of a hundred feet. The thickness of this glacier has been greatly overestimated. In reality, instead of being 1,800 to 2,500 feet thick, it does not appear where greatest to be more than a few hundred, for at a number of places it is so thin that its bed is exposed. Its terminal moraine is a huge pile, nearly half a mile in width, measured in the direction of glacial motion.
Next south of the Hottum glacier is the Wintum, which attains a length of over two miles, and ends with an abrupt front of ice in a cañon. Upon the southeastern slope of Mt. Shasta, at the head of a large cañon, is the Konwakitong glacier. Notwithstanding its diminutive size, its crevasses and the muddy stream it initiates indicate clearly that the ice mass continues to move. The amount of moraine material upon its borders is small, and yet, of all the glaciers about Mt. Shasta, it is the only one which has left a prominent record of important changes. The country adjacent to the west side of the Konwakitong cañon has been distinctly glaciated so as to leave no doubt that the Konwakitong glacier was once very much larger than it is at the present time. The rocks on which it moved have been deeply striated, and so abraded as to produce the smooth, rounded surfaces so common in glaciated regions. At the time of its greatest extension the glacier was 5.8 miles in length and occupied an area of at least seven square miles, being over twenty times its present size. Its limit is marked at several places by a prominent terminal moraine. The thickness of the glacier where greatest was not more than 200 feet, for several hills within the glaciated area were not covered. The striated surfaces and moraines do not extend up the slopes of those hills more than 200 feet above their bases. The thinness of the glacier is completely in harmony with the limited extent of its erosion, although the rocks are distinctly planed off, so that the low knobs and edges have regularly curved outlines. It is evident that a great thickness of rock has been removed by the ice, and that the period of ice erosion has been comparatively brief. During the lapse of time, however, there have been important climatic oscillations, embracing epochs of glacial advance and recession. None of the glaciers about Mt. Shasta, excepting the Wintum, terminate in cañons, but all of them give rise to muddy streams which flow in cañons to the mountain’s base. The cañons are purely the product of aqueous erosion, and contain numerous waterfalls, whence the streams in descending leap over the ends of old lava flows 50 to 300 feet in height.
In strong contrast with the arctic condition of Mt. Shasta to-day, are the circumstances attending its upbuilding, when it was an active volcano belching forth streams of fiery lava that flowed down the slopes now occupied by ice. It is the battlefield of the elements within the earth against those above it. In its early days the forces beneath were victorious, and built up the mountains in the face of wind and weather, but gradually the volcanic energy died away and the low temperature called into play those destructive agents which are now reversing the process and gradually reducing the mountain toward a general level. A microscopical examination of the rocks of Mt. Shasta reveals the fact that it is composed chiefly, if not wholly, of three kinds of lava. Several small areas of metamorphic rocks occur within its borders, but there is no evidence to show that they form any considerable portion of the mountain.
The range in mineralogical composition of the lavas is not extensive. There are only four minerals which deserved to be ranked as essential and characteristic constituents: they are plagioclase, feldspar, pyroxene, generally in the form of hypersthene hornblende, and olivine. The kind of lava which has by far the widest distribution upon the slopes of Mt. Shasta is composed essentially of plagioclase, feldspar and hypersthene, with some angite, and belongs to the variety of volcanic rocks which, on account of composition, and the place where first discovered, has been designated hypersthene andesite. Lava of this type has been shown by Messrs. Cross and Giddings of the Geological Survey to be widely distributed beyond the Mississippi. Upon the western slope of the mountain, especially in the vicinity of the prominent volcanic cone, the form of which suggests its name sugar loaf, the lava contains prominent crystals of hornblende instead of so much hypersthene and angite, and closely resembles the celebrated hornblende andesite lava from among the extinct volcanoes of central France. The third variety of lava which enters into the structure of Mt. Shasta is familiar to every one as basalt. It occurs in relatively small quantities, and has been extruded low down upon the slopes of the mountain. From the fact that there are three kinds of lava in the structure of Mt. Shasta, it must not be concluded that they all issued from the same volcanic vent, nor that they were effused from three separate and distinct openings. In reality, contributions to the upbuilding of Mt. Shasta have been made by over twenty volcanic orifices, of which two have been principal and far more prolific than all the parasitic events combined. This enumeration does not include those large fissures in the side of the cone, which are evidently attributable to the hydrostatic pressure of the molten mass within. The small number of parasitic cones on the slopes of Mt. Shasta is somewhat remarkable, especially when we compare it with the largest volcano in Europe. Although it is much higher than Etna, its base is less expansive, and its size about half that of the mighty monarch of the Mediterranean. Upon the irregular slopes of Etna there are 200 prominent subsidiary cones, beside over 400 of smaller size. On the contrary, Mt. Shasta has but a score of such accessories, and the remarkable regularity of its acute form forcibly expresses the highly concentrated type of volcanic energy which it represents.