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To an eastern friend familiar with the Swiss Alps I recently showed an aerial photograph of Mount Whitney. “What!” he exclaimed, in evident disappointment, “is the summit of Mount Whitney flat and featureless? I had imagined our highest peak to be a towering rock monument with sharp, sky-piercing summit.” “Yes,” was my reply, “Mount Whitney’s summit is merely a broad, gently sloping platform, which, I suppose, holds little appeal for an energetic mountaineer like you, but to a geologist specializing in the study of mountain uplifts and mountain sculpture that summit platform is a feature of quite unusual, indeed, altogether exceptional interest. I grant you that in point of spectacular beauty Mount Whitney cannot compare with the dazzling Jungfrau or the sharp-profiled Matterhorn, but, to one who can read it, the story told by its flat summit is far more significant and goes back to much more remote ages than any message conveyed by those glamorous alpine peaks. Indeed, the more fully I comprehend its story, by dint of repeated visits to and flights around and over Mount Whitney, the more venerable, the more precious seems that bit of flat land on its lofty summit. Upon it I have never set foot without a certain sense of reverence.”
Whereupon I was requested to explain.
Broadly speaking, in a mountain region of great altitude that is profoundly and thoroughly dissected by canyons and valleys, sharp crests and pointed peaks are the rule; for the precipitous sides of the canyons and valleys lead more or less directly up to the dividing ridges and summits, and there meet one another at acute angles. If, in addition, a region so dissected has been intensely glaciated, the sharpness of its crests and peaks is likely to be still more pronounced; for glaciers widen more than deepen the canyons they occupy, and this widening is done at the expense of the intermediate divides. The widening process, moreover, is carried all the way to the extreme canyon-heads, and as a result these are enlarged from V-shaped gulches and ravines to broadly U-shaped amphitheaters, or cirques. Biting into the mountains from opposite sides these cirques transform the crests and spurs between them to attentuated comb-ridges or cleavers, and sharpen the peaks to three- or four-edged pyramids with concave sides. These types of mountain sculpture are familiar to all who have climbed in the Alps, or for that matter, in other strongly glaciated alpine regions. They are characteristic also of the High Sierra, and predominate in any extended view of it.
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Figure 12.—Idealized representation of a portion of the tilted Sierra block, showing the “roots”
of the ancestral Sierras penetrating deep into the granite; also longitudinal crests and valleys.
Vertical scale exaggerated
Mount Whitney’s gently sloping tabular summit, it will be readily seen, belongs to an entirely different category. It is manifestly not an alpine mountain form. It could not possibly have been fashioned at its present high level by the erosional processes described. On the contrary, it is being destroyed by them; for, as the surrounding precipices continue to crumble and spall off, the platform will grow smaller and smaller until at last it will cease to exist. Evidently, it is a much older feature than any of the sharply sculptured alpine peaks around it; it is a remnant of an ancient landscape, the rest of which already has been carried away. What manner of landscape was this? How was it formed, and how long ago?
Be it understood, at the outset, that the Sierra Nevada, which is a huge tilted block of the earth’s crust, slanting toward the west, is not the first mountain range to occupy the region east of the Great Valley of California. Long before it was uplifted, another mountain range, or to be more accurate, a system of mountain ranges, stood in the same place. And that earlier mountain system, itself, was a late comer in geologic history; for it arose in the Mesozoic era, the era of giant reptiles, only about one hundred million years ago, after the earth had been troubled with spasmodic heavings and sinkings for upward of one and a half billion years.1 A complete record of all those successive disturbances probably will never be obtained, for the evidences grow more and more fragmentary, the farther back they are pursued; but this much is definitely known, that during those vast stretches of time the area now occupied by the Sierra Nevada was alternatingly ocean-bottom and land, and when it was land it bore, as a rule, hills and even mountains of some height.
With those remote and as yet vaguely known events we need not further concern ourselves in this study of Mount Whitney—though merely to be aware of their occurrence gives us a tremendous perspective of earth history. It is with the mountain system that preceded the advent of the present Sierra Nevada that we must begin. What has become of it? Are any of its mountains and valleys still in existence? No, they have been completely annihilated, eradicated from the face of the earth; but fortunately some of the roots, if we may call them such, remain incorporated in the body of the present Sierra, and from these it is possible with some confidence to infer the structure and even the topography of those ancestral Sierras. They were carved evidently from great wavelike folds or wrinkles in the earth’s crust produced by the buckling of originally flat lying strata, and they must have had the aspect of roughly parallel mountain ridges similar to those of the Appalachian system but trending in general from northwest to southeast. These ancestral Sierras were in existence for nearly 80 million years and in that time were gradually worn down by the processes of erosion until nothing remained, presumably, but rows of hills in a lowland that sloped gently down to the sea. Between those hills, which were composed of the more obdurate rocks, the streams followed belts of less resistant rocks, mostly in northwesterly or southeasterly directions.
Then, about 50 to 60 million years ago, shortly after the dawn of the Cenozoic era—the era of mammals and the latest great time divisions of geologic history—began the first uplifts that led to the rise of the present range. They tilted the Sierra region and the country to the east of it toward the southwest, and as a result a new system of southwestward flowing master streams came into existence; but many of the lesser streams between the ridges, unable to shift, maintained their southeasterly or northwesterly courses. Trenching deeper with every succeeding uplift, they eventually cut through the lowest of the folded strata and graved their valleys in the granite underneath—the granite which had welled up in a molten state from the depths of the earth and had crystallized under the folds of the ancestral Sierras. And so the northwest-southeast trend of those ancient mountains was perpetuated in the landscape of the present range.
Little attention—altogether too little—has been paid to the significance of the crests and valleys of the Sierra Nevada that trend in northwesterly or southeasterly directions, roughly parallel to the main crest-line and at right angles to the master canyons, which drain more or less directly down the western slope. These multiple crests, with their jagged peaks, have led us to speak, familiarly, of “the Sierras” and justify the use of the plural form. They are now seen to be the very oldest features in the landscape of the range, an inheritance from the long departed ancestral Sierras.
Some of the longitudinal crests of the Sierra Nevada are still composed of folded strata left from the earlier mountain system, but many of them are carved wholly out of granite. A striking example of the former kind is the Ritter Range, which is made largely of ancient folded volcanic rocks. The southeastward trending upper canyon of the Middle Fork of the San Joaquin, which parallels the Ritter Range as far south as the head of Pumice Flat, is cut in other volcanic rocks of the same relict mass, and closely follows the direction or “strike” of the
Aerial view of Mount Whitney and the Upper Kern Basin, with Table Mountain in the
distance. By Roy Curtis. Reno, Nevada
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Farther south, in the headwaters of the Kings River and in Sequoia National Park, where the folded structures of the ancestral Sierras bend gradually south-southeastward, the principal lineaments of the High Sierra notably bend in the same direction, although they are carved for the greater part out of granite. There, to mention only those most directly related to our theme, are the Great Western Divide, which contains stratified rocks in the vicinity of Mineral King and in the Kaweah Group; the upper Kern Canyon, which is cut entirely in granite, along a nearly straight north-south fault; and, to the east of it, the culminating crest of the Sierra Nevada, which bears Mount Whitney and is composed of granite throughout.
Aerial view of Mount Whitney and Mount Young with the Kaweah Peaks
beyond Kern Canyon. By Roy Curtis. Reno, Nevada
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The crest last mentioned deserves closer scruntiny. A distinct mountain range it is, stretching in a south-southeasterly direction for a distance of 17 miles—from the Shepherd Pass on the north, to the Cottonwood Pass on the south. Surmounted by seven of the eleven 14,000-foot peaks of the Sierra Nevada —Tyndall, Williamson, Barnard, Russell, Whitney, Muir, and Langley—and
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Figure 13.—East-west profile of Mount Whitney. The broken line
indicates the approximate outlines of ancient ‘’Whitney Hill.”
Vertical scale same as horizontal scale
That the Muir Crest, like the other longitudinal crests cited, has inherited its southeasterly trend from the ancestral Sierras, seems hardly open to doubt, for there is nothing in the joint-structure of its granitic rocks that could have determined that trend. The Kern Canyon, to the west of it, differs it is true, from the rank and file of longitudinal valleys in the Sierra Nevada in that its course is determined by a fault, a long fracture in the Sierra block, but, to judge from the older features of its landscape and from its great breadth, the upper Kern Basin as a whole has been developed from a very ancient valley and is essentially analogous to Center Basin and the canyons of East Creek and Sphinx Creek, to the north, and Cloud Canyon, to the northwest. It probably antedates the fault, though it is possible that the fault, too, is of great antiquity.
A number of features on the east flank of the Muir Crest, furthermore, point unmistakably to the former existence, several miles farther to eastward, of another longitudinal valley of great antiquity, a valley that long antedated the down-faulting of Owens Valley and the formation of the imposing east front of the Sierra Nevada. Most definite is the evidence presented by the eastern spur of Mount Le Conte which terminates in Lone Pine Peak, and by similar spurs east of Mount Langley. There is, therefore, ample warrant for the belief that the Muir Crest was developed, by valley-deepening to the west and the east of it, from a row of lowland hills, relics of the destroyed ancestral Sierras.
Is it then to be inferred, you may ask, that the summit platform of Mount Whitney is a remnant of one of those ancient lowland hills? A daring thought, it seems, yet that is precisely what its configuration appears to indicate. Indeed, that summit platform has, so far as it is preserved, all the characteristics of a lowland hill. Its gentle westward slope could not possibly have been fashioned
Aerial view of Mount Whitney (from the north). Mount Russell. Mount Hitchcock,
and Mount Langley. By Francis P. Farquhar
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The landscape of the High Sierra affords many bits of supporting evidence for this interpretation of Mount Whitney’s origin. In the first place, Mount Langley’s summit, which is but a few hundred feet lower than Mount Whitney’s, is of the same gently sloping tabular type. Its summit profile, when carefully plotted like that of Mount Whitney, and then extended westward to the axis of Rock Creek Canyon, indicates for the original “Langley Hill” a height closely comparable to that of “Whitney Hill.”
Again, the Great Western Divide and its long north-northwestward and south-southeastward trending spurs, which must have originated in much the same way as the Muir Crest, bear several peaks with flat or gently sloping tabular summits. Most noteworthy is Table Mountain (13,646), but hardly less typical, though less clean cut, is the tabular peak (13,300) between Milestone Mountain and the Colby Pass, which might well be called Milestone Mesa. And on the Kern Ridge nearby are two more unnamed mountains with gently sloping summit platforms, 13,560 and 13,206 feet high, respectively. These tabular summits ranging within a few hundred feet of one another in altitude, clearly represent remnants of a group of ancient hills. The fact that they average about 1000 feet lower in altitude than the comparable summits on the Muir Crest does not argue against the probability of their having been derived from the same ancient landscape as the latter, for the Great Western Divide stands 10 to 15 miles west of the Muir Crest and consequently about a thousand feet lower on the westward sloping body of the Sierra Nevada.
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Aerial view of the Muir Crest. Lone Pine and the Alabama Hills in the foreground.
By Roy Curtis, Reno, Nevada
Farther north in the range still other tabular peaks dominate its sky line. Notable examples are Mount Darwin, which has two detached summit platforms, 13,841 and 13,701 feet in altitude, respectively; and Kuna, Koip, and Blacktop peaks, in Yosemite National Park, which together form a continuous platform 3 1/2 miles long and ranging between 12,500 and 13,000 feet in altitude. Parker Peak (12,850), Mount Gibbs (12,700), and Mount Dana (13,050) bear remnants of the same ancient undulating landscape. The acuminate peak of Mount Dana is the most prominent hill of all, but even it rises only 700 feet above the platform at its east base. To those who have firsthand acquaintance with these crests it is readily evident that their tabular summits, which decline steadily northward with the entire body of the range, represent isolated remnants of a once continuous landscape of moderate relief, an ancient lowland now raised to great height on the present range.
It is now in order to relate briefly how by successive steps lofty Mount Whitney has evolved from lowly “Whitney Hill.” This story, of course, has to do primarily with the successive uptiltings of the Sierra Nevada and the cycles of erosion that were initiated by them. But where, you will probably ask, is the record of those uplifts to be found? In the features of the landscape itself. Professor Lawson was the first to spell out the principal chapters of that history from an analysis of the landscape of the upper Kern Basin, and that classic analysis will here be followed, though with certain modifications and additions indicated by the more complete knowledge now at hand.3
Be it observed, in the first place, that Mount Whitney outtops by fully one thousand feet all the other mountains in its immediate neighborhood that have rounded or gently sloping summits—notably Mount Young4 (13,493) and Mount Hitchcock (13,188). The disparity in height is manifest in the aerial view looking northwestward over Mount Whitney and Mount Young. It is likewise patent from the profile plot in Figure 13, which shows that the summit of Mount Young originally rose but a few hundred feet above the vale at the west base of “Whitney Hill.” Mount Langley similarly outtops the rounded summit (13,481) of the unnamed massif to the west of Rock Creek Canyon, as well as Lone Pine Peak (12,951), to the northeast, and Cirque Peak (12,863), to the south. The smoothly curving slopes of these lesser mountains, moreover, descend to levels close to 12,000 feet, and appear to have been fashioned with reference to much lower valley-floors than the summit platforms of either Mount Whitney or Mount Langley. It is to be inferred, therefore, that the intial uplift of the region caused the streams to intrench themselves a thousand feet or more on both sides of the Muir Crest. During the ensuing stillstand of the earth’s crust their valleys widened gradually and the mountain slopes were worn back to moderate angles. Mount Whitney, as a result of this first uplift, probably gained some two thousand feet in altitude above the sea, and, because of the valley-cutting, came to stand 500 or 600 feet higher above its immediate base. Moreover, long spurs were carved on both sides of the Muir Crest, spurs such as are now represented by Mount Young and Lone Pine Peak.
To the west of Cirque Peak, and about 1500 feet below the level of its rounded summit, is an undulating plateau that stretches unbroken for a distance of seven miles toward the Kern Canyon. The principal valley on that plateau, broad and level, goes by the name of Siberian Outpost. For the summit tract, which is of far greater extent than the valley, and even more frigid and more windswept, the name Boreal Plateau has recently been proposed. This plateau unquestionably represents a large remnant of an erosion surface of moderate relief that was formed throughout the upper Kern Basin during a prolonged period of erosion following a second great uplift. Other remnants of this ancient erosion surface are Guyot Flat, to the northwest of Mount Guyot, and the Bighorn Plateau, between Wallace Creek and Tyndall Creek. The valley profiles for this stage of development of the upper Kern Basin are not all drawn at the time of this writing, and consequently only rough estimates can here be given for the magnitude of the second uplift and the consequent further gain in height of Mount Whitney. The peak was raised presumably about 3000 feet higher, and therefore attained an altitude of, roughly, 7000 feet above the sea. As a result of further valley cutting by Whitney Creek its height above its west base was increased probably to somewhat more than 2000 feet.
About 1500 feet below the general level of the Boreal Plateau, again, lie the broad, gently sloping rock-benches that flank the Kern Canyon proper. Representative of these is the Chagoopa Plateau, which rises from an elevation of 8600 feet at the canyon rim to about 10,500 feet at the base of the mountains. Those benches clearly are remnants of a former floor of the Kern Basin that was developed to great breadth during an erosion cycle following a third uplift. The magnitude of that uplift also can, for the present, only be estimated roughly. It amounted probably to some 2000 feet, and therefore raised the summit of Mount Whitney to an altitude of about 9000 feet.
The Kern Canyon itself was, of course, trenched in consequence of the last
great uplift. That uplift took place, to judge from the best data now available,
about the beginning of the Ice Age, and the canyon is therefore really a product
of alternating stream and glacial erosion. Like the Yosemite, its upper portion
was three times invaded and remodeled by a mighty trunk glacier, and to the
repeated glacial remodeling it owes its pronounced U-shape. The depth of the
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Table Mountain on the Great Western Divide, with its gently sloping tabular summit,
represents the same ancient landscape surface as Mount Whitney and other summits on
the Muir Crest, ten miles to the east. Milestone Mountain in the middle distance with the
Red Spur on the skyline.
The recency of the last uplift accounts also for the slight headway which Whitney Creek has made in cutting its valley down to the level of the main
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Trail to Mount Whitney. By Cedric Wright
The extent to which the upland valley of Whitney Creek has been remodeled by glacial action varies considerably in its different parts. In its lower portion where the ice never exceeded 600 feet in depth—as is shown by the lateral moraines—the valley suffered but moderate changes, but at the immediate base of Mount Whitney, where the two branches of the “Whitney Glacier” coalesced, a radical transformation was effected. The ice there attained a depth of over 1000 feet, and because of this greater depth and the longer duration of its action, it was able to add several hundred feet to the depth of the canyon and even more to its breadth. There can be no doubt that the present broad U-shape of Whitney Canyon was evolved by glaciation from a relatively narrow preglacial V-shape, but so thoroughgoing has been the transformation that it is difficult from the present topography to judge what the preglacial features may have looked like.
During the first half of the Ice Age there also took place the tremendous dislocation of the earth’s crust that resulted in the formation of the imposing eastern front of the Sierra Nevada. Opinions of geologists still differ as regards the precise nature of that dislocation, but it seems probable from the latest field data now at hand, that it consisted in the main of a sinking of Owens Valley between parallel faults at the bases of the Sierra Nevada and the Inyo Range; also, that this subsidence occurred after the Sierra Nevada had attained approximately its present height and had suffered its first glaciation. The dislocation probably was not instantaneous, but was effected by many successive jerky movements spaced at intervals over a period thousands of years in length.
While it was thus growing, the eastern front of the Sierra Nevada was constantly subject to erosion, the more intense because of its steepness, and so it became deeply gashed by canyons and gulches. The extent to which it has been dissected and worn back is at first difficult to evaluate. Standing on the extreme summit of Mount Whitney, at the brink of its great east-facing cliff, one is apt to gain the impression that the fault fracture is right at one’s feet, yet it is manifest from the projecting spur that terminates in Lone Pine Peak, and from the long spurs to the east of Mount Langley, all of which bear remnants of ancient erosion surfaces, that the original fault escarpment must have stood at least four or five miles east of Mount Whitney’s summit.
Stream erosion on the eastern front of the range was supplemented at least twice by glacial erosion, most vigorously at the heads of the canyons and gulches, less so toward their lower ends. Capacious cirques were developed on the northerly and easterly sides of the peaks, and as the curving cirque walls receded under the combined attacks of quarrying glaciers and rock-splitting frosts, they bit deeper and deeper into the body of the Muir Crest, destroying the old preglacial slopes and spurs, carrying away even the main divide, as in the stretch between Mount Whitney and the Whitney Pass, where only the western slope now remains. In some places, as to the south of Mount Le Conte, the divide, attacked from both sides, was transformed to a narrow, pinnacled comb-ridge; elsewhere, as between Mount Whitney and Mount Russell, it was reduced by the headward quarrying of opposing glaciers to a low, frail rock-partition, and in a few spots, as between Mount McAdie and Mount Mallory, the divide was demolished altogether and replaced by a smoothly concave saddle or col.
A very massive, full-bodied mountain preglacial Mount Whitney must have
been, else it would have been reduced, like its smaller neighbor, Mount Russell,
to an attenuated alpine crag. To judge from its present outlines, its entire eastern
half has been cut away by cirque glaciers. Those glaciers were small but doubtless
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Wasting blocks of aplite. summit of Mount Whitney. By François Matthes
From the north side of the mountain a broad slice was removed by the widening of the glacial canyon that lies between it and Mount Russell, and on the
west side the lower preglacial slope was destroyed by the glacial widening of
Whitney Canyon. The southeast side lost a small slice as a result of the incision
of a narrow cleft, the northernmost of the series of clefts that gash the crestline
at intervals for more than a mile to the south of Mount Whitney. These clefts—
the breathtaking “windows” that afford occasional peeps to the eastward from
the trail—are not glacial features, but have been etched out, so to speak, by frost
action seconded by snow avalanches along vertical zones in which the granite as
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House on Mount Whitney and frost-heaved blocks of aplite. By François Matthes
One of the most astounding features of Mount Whitney is that, although situated in the center of a district from which glaciers formerly radiated in all directions, its own summit platform and the upper portions of its sides have remained unglaciated. Not the slightest evidence of glacial action, whether in the form of polish, striae, or moraines, is to be found on the summit platform; and as for the canyons at the immediate base of the mountain, these, it is clear from the moderate height to which their walls appear smoothed by lengthwise glacial corrasion, were never filled with ice to more than one-half of their depth. The effects of glacial corrasion which they exhibit are, of course, only those produced by the later glaciers, but it is manifest from the height and the gradients of the older moraines on the sides of Whitney Canyon that the earlier glaciers, there as in other parts of the Sierra Nevada, had no greater depth in the cirques and upper canyons than the later glaciers.
A similar dearth of glacial ice prevailed throughout the entire extent of the Muir Crest, as is shown by the low “ice lines” in all its canyons and by its numerous unglaciated summits and spurs. This state of things, which must have contrasted with the superabundance of glacial ice in the upper San Joaquin and upper Tuolumne basins, was due in part to the position of the Muir Crest close to the southern limit of glaciation in the Sierra Nevada, which coincides approximately with the southern limit of the High Sierra, properly speaking; and in part, also, to the fact that the Muir Crest was then, as now, robbed of its rightful share of snow by the Great Western Divide, upon which the snow clouds, driven up by southwesterly winds, unload the bulk of their white burden.
The sides of Mount Whitney, in so far as they rise above the level of the ancient glaciers, are furrowed by parallel or converging gullies, as much as 50 or even 100 feet in depth. Where these are spaced at close intervals, they are separated only by sharp, craggy rock-ribs, and the cliffs have a distinctly fluted appearance in consequence. These gullies, it is now realized, have been worn, not by streams of water, but by avalanchess of snow shod with rocks. They are, indeed, characteristic forms of avalanche sculpture that have not until recently been recognized as such in this country. The bottoms of these gullies are smoothly concave, as a result of the rasping action of frequent avalanches, and remind one of coal chutes such as are used for the unloading of coal cars or coal trucks by gravity. The term “snow chutes” (or perhaps “avalanche chutes”) therefore seems appropriate for them.
Snow chutes are numerous on both the north and west sides of Mount Whitney, but those on the west side are developed on the grandest scale. Still more perfect, though perhaps less deep, are the snow chutes on the north side of Mount Hitchcock and in the cirque at the head of Whitney Canyon. The Mount Whitney district is, in fact, remarkably rich in avalanche sculpture, far richer than the Great Western Divide and many other parts of the high Sierra, the principal reason being that its granitic rocks have a fairly regular joint structure. In many alpine regions where avalanches are active in winter, snow chutes are only imperfectly developed or entirely absent, because the rock structure is too irregular.
That the snow chutes in the sides of Mount Whitney were carved chiefly
during the Ice Age, while the canyons were being glaciated, is evident from the
fact that they end invariably at or close to the “ice line,” which marks the upper
limit of glacial corrasion on the canyon walls. Avalanches have occurred, of
course, through all of postglacial time and are active in winter even now, but all
of this postglacial avalanching has added but little to the depth of the chutes,
Milestone Basin with Mount Whitney in the distance. By Walter L. Huber
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The snow conditions that prevail on the summit platform of Mount Whitney, and that have prevailed there throughout all glacial times, are intimately related to the development of the snow chutes in its sides. The avalanches are composed today, and doubtless have always been composed, in large part of snow blown from the summit platform by the winter gales. Because of its simple configuration, unaccidented by ridges, pinnacles, or ravines, that platform is wind-swept throughout and in every direction. As a consequence the greater part of the snow that falls upon it is blown off by the winds while still in a powdery state. As westerly gales are most prevalent the bulk is flung out to eastward in great “snow banners,” such as Muir described many years ago, and swirls down in the “wind shadow” of the peak; but considerable portions of it are blown also in other directions and accumulate in massive cornices at the edges of the platform. It is the breaking down of these overhanging, unstable cornices that gives rise to the avalanches.
Those who have observed Mount Whitney in winter say that its summit is never more than thinly mantled with snow. Sometimes it is even partly bare when the valleys at lower levels are smothered beneath heavy loads of snow. The same is true of all the tabular summits of the Sierra Nevada. What is more, there is good reason to believe that closely similar conditions prevailed on them during glacial times, for the climate then was not more snowy but colder. It is entirely possible, even, that those lofty summits then bore less snow than they bear today, for because of the more intense cold the winter gales were more violent, and the zone of maximum snowfall, which today lies, according to the best data available, fully 3000 to 4000 feet below the level of the main peaks, then probably lay lower still, so that the peaks rose high into regions of relatively scant precipitation.
The summit of Mount Whitney not only has escaped glaciation, but, what may seem more astonishing, it has escaped stream erosion also, during all of glacial, interglacial, and postglacial times. Not a single streamworn gully cuts its surface, nor is there any more than the merest trace of a rainwater rill. The reason is that heavy showers are rare at its high altitude. Even in midsummer the precipitation consists in large part of snow pellets—graupel is the technical term—and the snowdrifts waste away chiefly by direct evaporation under the intense radiant heat of the sun, as is attested by their deeply pitted surfaces.
The small amount of meltwater that issues from the snowdrifts, nevertheless, is a source of considerable destructive energy. Congealing night after night in the crevices of the rock, it loosens up the joint blocks and in the course of time splits them into smaller and smaller fragments. The results are familiar to every mountaineer who has visited any of the tabular summits of the Sierra Nevada. They are all encumbered with frost-riven and frost-heaved blocks that make progress excessively wearisome. This type of intense frost work on unglaciated surfaces at high altitudes (and in high latitudes too) has been termed nivation, because it is dependent upon the presence of snowfields and snowdrifts. The top of Mount Whitney, accordingly, is properly described as a nivated summit.
It is a pertinent question at what rate the process of nivation works. How fast, or rather, how slowly is it reducing Mount Whitney in height? No observational data are at hand on which a quantitative estimate may be based, but this much can be said without fear of contradiction, that the nivation process works in general far more slowly than either stream-and-rain erosion or glacial erosion. Much depends on the character of the rock. In thin-bedded or slaty rocks that break up into shingle and small flaky fragments, an auxiliary process known as solifluction (literally soil-flow) sets in, that operates to remove the frost-split material. It consists of a sluggish flowlike movement that is particularly active in masses of fine material permeated and lubricated with water, causing them to gravitate down slope in tonguelike bodies that push the coarser shingle up on edge. But in the granitic rocks of the Sierra Nevada, which break up for the most part into large and heavy blocks, or locally into loose sand through which water passes as through a sieve, solifluction is not effective as a transporting agent, and as a consequence the frost-split material remains largely in place. Reduction by nivation there is necessarily very slow.
It happens that the summit of Mount Whitney is composed in large part of a fine-grained, siliceous type of granite known as aplite—the kind of rock which ordinarily occurs only in narrow dikes (veins, as they are commonly but erroneously called). This rock breaks up characteristically into large angular slabs and weathers down to sand far more slowly than the coarse-grained granite roundabout. It follows that on Mount Whitney solifluction is wholly inoperative and nivation works even more slowly than on some of the other tabular peaks of the Sierra Nevada. How slowly, you ask? Perhaps as slowly as three or four feet in 250,000 years, to judge from the rate at which certain dikes of aplite whose glacial history is definitely known appear to have been reduced by weathering. As the Ice Age and all of postglacial time together aggregate in round numbers one million years, it would follow that Mount Whitney has suffered a reduction of only 12 or 16 feet since the Ice Age began. The total reduction which Mount Whitney has suffered by erosion of all kinds since it was a lowland hill, considering the climatic conditions and the vegetational cover that existed in preglacial times, probably amounts to several hundred feet.
Remains the question, how old is Mount Whitney? How many millions of years have elapsed since it was a lowland hill? Again, only a rough estimate is
The best method of approach is by evaluating the duration of each of the successive cycles of erosion that have left their impress on the region (see Fig. 14). Without going into a full discussion of all the factors that must be considered, it may be pointed out that the Kern Canyon has been produced by stream and glacial erosion since the last great uplift of the range. It is therefore presumably about one million years old. The broad rock-benches of the Chagoopa cycle, by comparison, must have required 10 to 15 times as long an interval for their development—in round numbers, 10 to 15 million years. The still more maturely developed landscape of the Boreal Plateau cycle, then, may have required fully 20 million years, and at least another five to ten million years is to be assigned to the cycle that followed the initial uplift. The total length of time that has elapsed since the lowland stage, when Whitney Hill was only 1500 feet high, therefore appears to be of the order of 35 to 45 million years.
Reprinted from Sierra Club Bulletin, 1937, pages 1-18.
1See footnote on page 97, and Appendix.—Ed.
2The small peak that bears Muir’s name at present seems hardly commensurate in importance among the features of the Sierra Nevada with the greatness of the man whose love for the “Range of Light” inspired the movement for the conservation of its scenic treasures.
3“The Geomorphogeny of the Upper Kern Basin,” by Andrew C. Lawson, in University of California Publications, Bulletin of the Department of Geology, 1904, 3:15, pp. 305—330.
4Since this essay was originally written, the higher part of Mount Young has been given the name Mount Hale.—Ed.
and Half Dome,
By Ansel Adams
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