All the valleys and cañons of the western flank of the Sierra, between 36° and 39° north latitude, naturally classify themselves under two genera, each containing two species. One genus comprehends all the slate valleys, the other all that are built of granite. The latter is far the more important, both on account of the greater extent of its geographical range and the grandeur and simplicity of its phenomena. All the valleys of both genera are valleys of erosion. Their chief distinguishing characteristic may be seen in the following descriptions:
1. Cross-sections, V-shaped, or somewhat rounded at bottom, walls irregular in structure, shattered and weak in appearance, because of the development of slaty cleavage planes and joints, which also prevent the formation of plane-faced precipice. Bottom showing the naked bed-rock, or covered by rocky debris, and sloping in the direction of the trend. Nearly all of the foothill valleys belong to this species. Some of the older specimens are smoothly covered with soil, but meadows and lakes are always wanting.
2. More or less widened, branching at the head. Bottom, with meadows, or groves or lakelets, or all together. Sections and wads about as in No. 1. Fine examples of this species occur on the head-waters of the San Joaquin.
1. Cross-sections narrowly or widely V-shaped. Walls seldom interrupted by side cañons, magnificently simple in structure and general surface character, and presenting plane precipices in great abundance. Bottom sloping in the direction of the trend, mostly bare, or covered with unstratified glacial and avalanche bowlders. Groves and meadows wanting.
2. Branching at head, with beveled and heavily abraded lips at foot. Bottom level meadowed, laked, or groved. Walls usually very high, often interrupted by side cañons. Sections as in No. 1. To this species belongs the far-famed Yosemite who origin we will now discuss.
We will henceforth make use of the word Yosemite both as a specific and geographical term.
Yosemite Valley is on the main Merced, in the middle region of the range. It is about seven miles long from east to west, with an average width at bottom of a little more than half a mile, and at the top of a mile and a half. The elevation of the bottom above sea level is about 4,000 feet. The average height of the walls is about 3,000 feet, made up of a series of sublime rock forms, varying greatly in size and structure, partially separated from one another by small side cañons. These immense wall-rocks, ranged picturesquely together, do not stand in line. Some advance their sublime fronts far out into the open valley, others recede. A few are nearly vertical, but far the greater number are inclined at angles ranging from twenty to seventy degrees. The meadows and sandy flats outspread between support a luxuriant growth of sedges and ferns, interrupted with thickets of azalea, willow and briar-rose. The warmer sloping ground along the base of the walls is planted with noble pines and oaks, while countless alpine flowers fringe the deep and dark side cañons, through which glad streams descend in falls and cascades, on their way from the high fountains to join the river. The life-giving Merced flows down the valley with a slow, stately current, curving hither and thither through garden and grove, bright and pure as the snow of its fountains. Such is Yosemite, the noblest of Sierra temples, everywhere expressing the working of Divine harmonious law, yet so little understood that it has been regarded as “an exceptional creation,” or rather exceptional destruction accomplished by violent and mysterious forces. The argument advanced to support this view is substantially as follows: It is too wide for a water-eroded valley, too irregular for a fissure valley, and too angular and local for a primary valley originating in a fold of the mountain surface during the process of upheaval; therefore, a portion of the mountain bottom must have suddenly fallen out, letting the super-incumbent domes and peaks fall rumbling into the abyss, like coal into the bunker of a ship. This violent hypothesis, which furnishes a kind of Tophet for the reception of bad mountains, commends itself to the favor of many, by seeming to account for the remarkable sheerness and angularity of the walls, and by its marvelousness and obscurity, calling for no investigation, but rather discouraging it. Because we can not observe the bed-rock to ascertain whether or not it is fractured, this engulfment hypothesis seems to rest safely under cover of darkness, yet a film of lake gravel and a meadow blanket are its only concealments, and, by comparison with exposed sections in other Yosemites where the sheer walls unite with the solid, unfissured bottom, even these are in effect removed. It becomes manifest, by a slight attention to facts, that the hypothetical subsidence must have been limited to the valley proper, because both at the head and foot we find the solid bed-rock.
The breaking down of only one small portion of the mountain floor, leaving all adjacent to it undisturbed, would necessarily give rise to a very strongly marked line of demarcation, but no such line appears; on the contrary, the unchanged walls are continued indefinitely, up and down the river cañon, and lose their distinguishing characteristics in a gradual manner easily accounted for by changes in the structure of the rocks and lack of concentration of the glacial energy expended upon them. That there is comparatively so small a quantity of debris at the foot of Yosemite walls is advanced as an argument in favor of subsidence, on the grounds that the valley is very old, and that a vast quantity of debris must, therefore, have fallen from the walls by atmospheric agencies, and that the hypothetical “abyss” was exactly required to furnish storage for it. But the Yosemite Valley is not very old. It is very young, and no vast quantity of debris has ever fallen from its walls. Therefore, no abyss was required for its accommodation.
If, in accordance with the hypothesis, Yosemite is the only valley furnished with an abyss for the reception of debris, then we might expect to find all abyssless valleys choked up with the great quantity assumed to have fallen; but, on the contrary, we find their debris in the same condition as in Yosemite, and not more abundant. Indeed, in some portions of valleys as deep and sheer as Yosemite there is absolutely no talus, and that there never has been any is proved by both walls and bottom being solid and ice-polished. Many examples illustrative of this truth may be seen in the great Tuolumne and Kings River valleys.
Where the granite of Yosemite walls is intersected with feldspathic veins, as in the lowest of the Three Brothers and rocks near Cathedral Spires, large masses are loosened, from time to time, by the action of the atmosphere, and hurled to the bottom with such violence as to shake the whole valley; but the aggregate quantity which has been thus weathered off, so far from being sufficient to fill any great abyss, forms but a small part of the debris slopes actually found on the surface, all the larger angular taluses having been formed simultaneously by severe earthquake shocks that occurred three or four hundred years ago, as shown by their forms and the trees growing upon them. The attentive observer will perceive that wherever a large talus occurs, the wall immediately above it presents a scarred and shattered surface whose area is always proportional to the size of the talus, but where there is no talus the wall is invariably moutonée or striated, showing that it is young and has suffered little change since it came to light at the close of the glacial period. On the 23rd of March, 1872, I was so fortunate as to witness the sudden formation of one of these interesting taluses by the precipitation of the Yosemite Eagle Rock by the first heavy shock of the Inyo earthquake, whereby their local character and simultaneity of formation was fully accounted for. This new earthquake gave rise to the formation of many new taluses throughout the adjacent valleys, corresponding in every particular with the older and larger ones whose history we have been considering.
As to the important question, What part may water have played in the formation of Sierra valleys? we observe that, as far as Yosemite is concerned, the five large streams which flow through it are universally engaged in the work of filling it up. The granite of the region under consideration is but slightly susceptible of water denudation. Throughout the greater portion of the main upper Merced Valley the river has not eroded its channel to a depth exceeding three feet since it first began to flow at the close of the glacial epoch, although acting under every advantage of concentration and quick descent. The highest flood-mark the young river has yet recorded upon the clean glacial tablets of its banks is only seven or eight feet above the present level, at ordinary stages. Nevertheless, the aggregate annual quantity that formerly passed down these cañon valleys was undoubtedly far greater than passes at the present time, because on the gradual recession of the glaciers at the dose of the period, the supply would necessarily be more constant, from their melting all through the seasons. The evidence, however, is incontestable, which shows that the highest floods of Sierra rivers in the upper and middle regions of the range never much exceeded those of the present time.
Five immense glaciers from five to fifteen hundred feet in depth poured their icy floods into Yosemite, uniting to form one huge trunk, moved down through the valley with irresistible and never-ceasing energy, crushing and breaking up its strongest rocks, and scattering them in moraines far and near. Many, while admitting the possibility of ice having been the great agent in the production of Yosemite valleys, conjecture that earthquake fissures, or cracks from cooling or upheaval of the earth’s crust, were required to enable the glaciers to make a beginning and to guide them in the work. We have already shown [in the earlier chapter about mountain sculpture] that cleavage planes and joints exist in a latent or developed condition in all the granite of the region, and that these exert immense influence on its glacial erodibility. During five years’ observation in the Sierra, I have failed to discover a single fissure of any kind, although extensive areas of clean-swept glacial pavements afford ample opportunity for their detection, did they exist. Deep slots, with regular walls, appearing as if sawed, or mortised, frequently occur. These are formed by the disintegration of soft seams a few inches or feet in thickness, contained between walls of stronger granite. Such is the character of the so-called fissure said to exist in a hard portion of the south wall of Yosemite, opposite the Three Brothers, so frequently quoted in speculations upon the valley’s origin.
The greatest effects of earthquakes on the valley we have already noticed in avalanche taluses, which were formed by the precipitation of weak headlands, that fell like ripe fruit. The greatest obstacle in the way of reading the history of Yosemite valleys is not its complexity or obscurity, but simply the magnitude of the characters in which it is written. It would require years of enthusiastic study to master the English alphabet if it were carved upon the flank of the Sierra in letters sixty or seventy miles long, their bases set in the foothills, their tops leaning back among the glaciers and shattered peaks of the summit, often veiled with forests and thickets, and their continuity often broken by cross-gorges and hills. So also the sculptured alphabet cañons of the Sierra are magnificently simple, yet demand years of laborious research for their apprehension. A thousand blurred fragments must be conned and brooded over with studious care, and kept vital and formative on the edges, ready to knit like broken living bones, while a final judgment is being bravely withheld until the entire series of phenomena has been weighed and referred to an allunifying, all-explaining law. To one who can leisurely contemplate Yosemite from some commanding outlook, it offers, as a whole, a far more natural combination of features than is at all apparent in partial views obtained from the bottom. Its stupendous domes and battlements blend together and manifest delicate compliance to law, for the mind is then in some measure emancipated from the repressive and enslaving effects of their separate magnitudes, and gradually rises to a comprehension of their unity and of the poised harmony of their general relations.
Nature is not so poor as to possess only one of anything, nor
throughout her varied realms has she ever been known to offer
an exceptional creation whether of mountain or valley. When, therefore,
we explore the adjacent Sierra, we are not astonished to find
that there are many Yosemite valleys identical in general characters,
each presenting on a varying scale the same species of mural precipices,
level meadows, and lofty waterfalls. The laws which preside over
their distribution are as constant and apparent as those governing
the distribution of forest trees. They occur only in the middle
region of the chain, where the declivity is considerable and where
granite is Yosemitic in its internal structure. The position of
upon the Yosemitic zone indicates a marked and inseparable relation to
the ancient glaciers, which, when fully deciphered, amounts to cause and
effect. So constant and obvious is this connection between the various
Yosemites and the névé amphitheatres which
fountained the ancient ice-rivers, that an observer, inexperienced
in these phenomena, might easily
anticipate the position and size of any Yosemite by a study of the glacial
fountains above it, or the position and size of the fountains by a study of
their complementary Yosemite. All Yosemites occur at the junction of two
or more glacial cañons. Thus the greater and lesser
Yosemites of the Merced,
Hetch Hetchy, and those of the upper Tuolumne, those of Kings
River, and the San Joaquin, all occur immeditely below the confluence
of their ancient glaciers. If, in following down the cañon channel of the
Merced Glacier, from its origin in the névé
amphitheatres of the Lyell
group, we should find that its sudden expansion and deepening
at Yosemite occurs without a corresponding union of glacial tributary
and without any similar expansion elsewhere, then we might well be
driven to the doctrine of special marvels. But this emphatic deepening and
widening becomes harmonious when we observe smaller Yosemites
occurring at intervals all the way down, across the Yosemitic zone,
a tributary cañon unites with the trunk, until,
on reaching Yosemite
where the enlargement is greatest, we find the number of confluent
glacier-cañons is also greatest,
as may be observed by reference
to Fig. 1.
Fig. 1—Tuolumne Yosemite.
(A A A, Glaciers.)
Fig. 2.—Kings River Yosemite.
(B B B B, Glaciers.)
Fig. 3.—Merced Yosemite glaciers.
(A, Yosemite Creek; B, Hoffman;
C, Tenaya; D, South Lyell;
E, Illilouette; F, Pohono.)
Much stress has been laid on the mere uncompared arithmetical depth of Yosemite, but this is a character of no consequence to the consideration of its origin. The greatest Merced Yosemite is 3,000 feet deep; the Tuolumne, 2,000; another, 1,000; but what geologist would be so unphilosophical as to decide against the identity of their origin from difference in depth only. One pine tree is 100 feet high, lean and crooked, from repressing winds and the poverty of the soil which nourished it; while another, more fortunate in the conditions of its life, is 200 feet high, erect and vigorous. So, also, one Yosemite is 3,000 feet deep because of the favorable structure of its rocks and the depth and number of ice-rivers that excavated it; another is half as deep, because of the strength of its rocks, or the scantiness of the glacial force exerted upon it. What would be thought of a botanist who should announce that our gigantic Sequoia was not a tree at all, offering as a reason that it was too large for a tree, and, in describing it, should confine himself to some particularly knotty portion of the trunk? In Yosemite there is an evergreen oak double the size of ordinary oaks of the region, whose trunk is craggy and angular as the valley itself, and colored like the granite bowlders on which it is growing. At a little distance this trunk would scarcely be recognized as part of a tree, until viewed in relation to its branches, leaves and fruit. It is an admirable type of the craggy Merced cañon-tree, whose angular Yosemite does not appear as a natural portion thereof until viewed in its relation to its wide-spreading branches, with their fruit and foliage of meadow and lake.
We present a ground-plan of three Yosemite valleys, showing
the positions of their principal glaciers, and the relation of
their trends and areas to them. The large arrows in Figs. 1, 2,
3 show the positions and directions of movement of the main confluent
glaciers concerned in the erosion of three Yosemites. With regard
to the number of their main glaciers, the Tuolumne Yosemite may
be called a Yosemite of the third power; the Kings River
Yosemite, of the fourth power; and the Merced Yosemite, of the
fifth power. The granite in which each of these three Yosemites
is excavated is of the same general quality; therefore, the differences
of width, depth, and trend observed, are due almost entirely to
the number, magnitude, declivity and mode of combination of the
glacial system of each. The similarity of their ground-plans
is obvious from a single glance at the figures; their cross-sections
are no less similar. One of the most characteristic from each
of the valleys under consideration is shown in Figs. 4, 5 and
6, drawn on the same scale.
Fig. 4.—Section across the
Hetch Hetchy Valley, or
lower Tuolumne Yosemite
Fig. 5.—Section across the
Kings River Yosemite
Fig. 6.—Section across
Fig. 7.—Idealized section
across Merced Yosemite
The perpendicularity of Yosemite walls is apt to be greatly over-estimated. If the slopes of the Merced Yosemite walls were to be carefully measured with a clinometer at intervals of say 100 yards, it would be found that the average angle they make with the horizon is less than 50°, as shown in Fig. 7. It is not possible that the bottom could drop out of a valley thus shaped, no matter how great the upheaval or down-heaval, or side-heaval.
Having shown that Yosemite, so-called, is not unique in its
ground-plan or cross-sections, we will now consider
some of the most remarkable of its rock forms. The beautiful San
Joaquin Dome in the cañon of the San Joaquin, near the
confluence of the south fork, looking south (Fig. 9),
shows remarkable resemblance to the Yosemite Half Dome, as seen
from Tenaya Cañon (Fig. 8).
Fig. 10.—North Face of Half Dome,
Fig. 11.—North Face of Half Dome
of Kings River Yosemite Valley
Fig. 12 is a view of the back or south side of Half Dome, Yosemite,
showing its moutonée condition; Fig. 13 represents
El Capitan of Yosemite, situated on the north side of the valley;
Fig. 14, El Capitan of Big Tuolumne Cañon, near the middle,
situated on the north side; Fig. 15, El Capitan of Big Tuolumne
Cañon, near the head, situated on the north side.
The far-famed El Capitan rock presents a sheer cleaved front, over three thousand feet high, and is scarcely less impressive than the great dome. We have collected fine specimens of this clearly defined rock form from all the principal Yosemites of the region. Nevertheless, it also has been considered exceptional. Their origin is easily explained. They are simply split ends of ridges which have been broken through by glaciers.
For their perfect development the granite must be strong, and
have some of its vertical cleavage planes well developed, nearly
to the exclusion of all the others, especially of those belonging
to the diagonal and horizontal series. A powerful trunk glacier
must sweep past in front
nearly in the direction of its cutting planes, with small glaciers,
tributary to the first, one on each side of the ridge out of which
the Capitan is to be made.
When the principal surface features of the Sierra were being blocked out, the main ice-sheet was continuous and moved in a southerly direction, therefore the most perfect Capitans are invariably found on the north sides of valleys trending east and west. The reason will be readily perceived by referring to Fig. 8 of Chapter I.
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