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ALL California has been
glaciated, the low plains and valleys as well as the mountains. Traces of an
ice sheet, thousands of feet in thickness, beneath whose heavy folds the
present landscapes have been moulded, may be found everywhere, though
glaciers now exist only among the peaks of the high Sierra. No other
mountain chain on this or any other of the continents that I have seen is so
rich as the Sierra in bold, striking, well-preserved glacial monuments.
Indeed, every feature is more or less tellingly glacial. Not a peak, ridge,
dome, cañon, yosemite, lake basin, stream, or forest will you see that does
not in some way explain the past existence and modes of action of flowing,
grinding, sculpturing, soil-making, scenery- making ice. For,
notwithstanding the post-glacial agents - the air, rain, snow, frost, river,
avalanche, etc. - have been at work upon the greater portion of the range
for tens of thousands of stormy years, each engraving its own characters
more and more deeply over those of the ice, the latter are so enduring and
so heavily emphasized, they still rise in sublime relief, clear and legible,
through every after-inscription. The landscapes of North Greenland,
Antarctica, and some of those of our own Alaska, are still being fashioned
beneath a slow-crawling mantle of ice, from a quarter of a mile to probably
more than a mile in thickness, presenting noble illustrations of the ancient
condition of California, when its sublime scenery lay hidden in process of
formation. On the Himalaya, the mountains of Norway and Switzerland, the
Caucasus, and on most of those of Alaska, their ice mantle has been melted
down into separate glaciers that flow river-like through the valleys,
illustrating a similar past condition in the Sierra, when every cañon and
valley was the channel of an ice stream, all of which may be easily traced
back to their fountains, where some sixty-five or seventy of their top-most
residual branches still linger beneath protecting mountain shadows.
The change from one to
another of those glacial conditions was slow as we count time. When the
great cycle of snow years, called the glacial period, was nearly complete in
California, the ice mantle, wasting from season to season faster than it was
renewed, began to withdraw from the lowlands and gradually became shallower
everywhere. Then the highest of the Sierra domes and dividing ridges,
containing distinct glaciers between them, began to appear above the icy
sea. These first river- like glaciers remained united in one continuous
sheet toward the summit of the range for many centuries. But as the
snow-fall diminished, and the climate became milder, this upper part of the
ice-sheet was also in turn separated into smaller distinct glaciers, and
these again into still smaller ones, while at the same time all were growing
shorter and shallower, though fluctuations of the climate now and then
occurred that brought their receding ends to a standstill, or even enabled
them to advance for a few tens or hundreds of years.
Meanwhile, hardy,
home-seeking plants and animals, after long waiting, flocked to their
appointed places, pushing bravely on higher and higher, along every
sun-warmed slope, closely following the retreating ice, which, like shreds
of summer clouds, at length vanished from the new-born mountains, leaving
them in all their main, telling features nearly as we find them now.
Tracing the ways of glaciers,
learning how Nature sculptures mountain waves in making scenery beauty that
so mysteriously influences every human being, is glorious work.
The most striking and
attractive of the glacial phenomena in the Tipper Yosemite region are the
polished glacier pavements, because they are so beautiful, and their beauty
is of so rare a kind, so unlike any portion of the loose, deeply weathered
lowlands where people make homes and earn their bread. They are simply flat
or gently undulating areas of hard resisting granite, which present the
unchanged surface upon which with enormous pressure the ancient glaciers
flowed. They are found in most perfect condition in the subalpine region, at
an elevation of from eight to nine thousand feet. Some are miles in extent,
only slightly interrupted by spots that have given way to the weather, while
the best preserved portions reflect the sunbeams like calm water or glass,
and shine as if polished afresh every day, notwithstanding they have been
exposed to corroding rains, dew, frost, and snow measureless thousands of
years.
The attention of wandering
hunters and prospectors, who see so many mountain wonders, is seldom
commanded by other glacial phenomena, moraines however regular and
artificial-looking, caflons however deep or strangely modeled, rocks however
high; but when they come to these shining pavements they stop and stare in
wondering admiration, kneel again and again to examine the brightest spots,
and try hard to account for their mysterious shining smoothness. They may
have seen the winter avalanches of snow descending in awful majesty through
the woods, scouring the rocks and sweeping away like weeds the trees that
stood in their way, but conclude that this cannot be the work of avalanches,
because the scratches and fine polished strife show that the agent, whatever
it was, moved along the sides of high rocks and ridges and up over the tops
of them as well as down their slopes. Neither can they see how water may
possibly have been the agent, for they find the same strange polish upon
ridges and domes thousands of feet above the reach of any conceivable flood.
Of all the agents of whose work they know anything, only the wind seems
capable of moving across the face of the country in the directions indicated
by the scratches and grooves. The Indian name of Lake Tenaya is "Pyweak" -
the lake of shining rocks. One of the Yosemite tribe, Indian Tom, came to me
and asked if I could tell him what had made the Tenaya rocks so smooth. Even
dogs and horses, when first led up the mountains, study geology to this
extent that they gaze wonderingly at the strange brightness of the ground
and smell it, and place their feet cautiously upon it as if afraid of
falling or sinking.
In the production of this
admirable hard finish, the glaciers in many places flowed with a pressure of
more than a thousand tons to the square yard, planing down granite, slate,
and quartz alike, and bringing out the veins and crystals of the rocks with
beautiful distinctness. Over large areas below the sources of the Tuolumne
and Merced the granite is porphyritic; feldspar crystals an inch or two in
length in many places form the greater part of the rock, and these, when
planed off level with the general surface, give rise to a beautiful mosaic
on which the happy sunbeams plash and glow in passionate enthusiasm. Here
lie the brightest of all the Sierra landscapes. The range both to the north
and south of this region was, perhaps, glaciated about as heavily, but
because the rocks are less resisting, their polished surfaces have mostly
given way to the weather, leaving only small imperfect patches. The lowest
remnants of the old glacial surface occur at an elevation of from three to
five thousand feet above the sea-level, and twenty to thirty miles below the
axis of the Range. The short, steeply inclined canons of the eastern flank
also contain enduring, brilliantly striated and polished rocks, but these
are less magnificent than those of the broad western flank.
One of the best general views
of the brightest and best of the Yosemite park landscapes that every
Yosemite tourist should see, is to be had from the top of Fairview Dome, a
lofty conoidal rock near Cathedral Peak that long ago I named the Tuolumne
Glacier Monument, one of the most striking and best preserved of the domes.
Its burnished crown is about fifteen hundred feet above the Tuolumne Meadows
and ten thousand feet above the sea. At first sight it seems inaccessible,
though a good climber will find it may be scaled on the south side. About
halfway up you will find it so steep that there is danger of slipping, but
feldspar crystals, two or three inches long, of which the rock is full,
having offered greater resistance to atmospheric erosion than the mass of
the rock in which they are embedded, have been brought into slight relief in
some places, roughening the surface here and there, and affording helping
footholds.
The summit is burnished and
scored like the sides and base, the scratches and strim indicating that the
mighty Tuolumne Glacier swept over it as if it were only a mere boulder in
the bottom of its channel. The pressure it withstood must have been
enormous. Had it been less solidly built it would have been carried away,
ground into moraine fragments, like the adjacent rock in which it lay
embedded; for, great as it is, it is only a hard residual knot like the
Yosemite domes, brought into relief by the removal of less resisting rock
about it; an illustration of the survival of the strongest and most
favorably situated.
Hardly less wonderful is the
resistance it has offered to the trying mountain weather since first its
crown rose above the icy sea. The whole quantity of post-glacial wear and
tear it has suffered has not degraded it a hundredth of an inch, as may
readily be shown by the polished portions of the surface. A few erratic
boulders, nicely poised on its crown, tell an interesting story. They came
from the summit peaks twelve miles away, drifting like chips on the frozen
sea, and were stranded here when the top of the monument merged from the
ice, while their companions, whose positions chanced to be above the slopes
of the sides where they could not find rest, were carried farther on by
falling back on the shallowing ice current.
The general view from the
summit consists of a sublime assemblage of ice-born rocks and mountains,
long wavering ridges, meadows, lakes, and forest-covered moraines, hundreds
of square miles of them. The lofty summit peaks rise grandly along the sky
to the east, the gray pillared slopes of the Hoffman Range toward the west,
and a billowy sea of shining rocks like the Monument, some of them almost as
high and which from their peculiar sculpture seem to be rolling westward in
the middle ground, something like breaking waves. Immediately beneath you
are the Big Tuolumne Meadows, smooth lawns with large breadths of woods on
either side, and watered by the young Tuolumne River, rushing cool and clear
from its many snow and ice fountains. Nearly all the upper part of the basin
of the Tuolumne Glacier is in sight, one of the greatest and most
influential of all the Sierra ice rivers. Lavishly flooded by many a noble
affluent from the ice- laden flanks of Mounts Dana, Lyell, McClure, Gibbs,
Conness, it poured its majestic outflowing current full against the end of
the Hoffman Range, which divided and deflected it to right and left, just as
a river of water is divided against an island in the middle of its channel.
Two distinct glaciers were thus formed, one of which flowed through the
great Tuolumne Cañon and Hetch Hetchy Valley, while the other swept upward
in a deep current two miles wide across the divide, five hundred feet high
between the basins of the Tuolumne and Merced, into the Tenaya basin, and
thence down through the Tenaya Cañon and the Yosemite.
The map-like distinctness and
freshness of this glacial landscape cannot fail to excite the attention of
every beholder, no matter how little of its scientific significance may be
recognized. These bald, westward-leaning rocks, with their rounded backs and
shoulders toward the glacier fountains of the summit-mountains, and their
split, angular fronts looking in the opposite direction, explain the
tremendous grinding force with which the ice flood passed over them, and
also the direction of its flow. And the mountain peaks around the sides of
the upper general Tuolumne basin, with their sharp unglaciated summits and
polished rounded sides, indicate the height to which the glaciers rose;
while the numerous moraines, curving and swaying in beautiful lines, mark
the boundaries of the main trunk and its tributaries as they existed toward
the close of the glacial winter. None of the commercial highways of the land
or sea, marked with buoys and lamps, fences, and guideboards, is so
unmistakably indicated as are these broad, shining trails of the vanished
Tuolumne Glacier and its far-reaching tributaries.
I should like now to offer
some nearer views of a few characteristic specimens of these wonderful old
ice streams, though it is not easy to make a selection from so vast a system
intimately interbiended. The main branches of the Merced Glacier are,
perhaps, best suited to our purpose, because their basins, full of telling
inscriptions, are the ones most attractive and accessible to the Yosemite
visitors who like to look beyond the valley walls. They number five, and may
well be called Yosemite glaciers, since they were the agents Nature used in
developing and fashioning the grand Valley. The names I have given them are,
beginning with the northernmost, Yosemite Creek, Hoffman, Tenaya, South
Lyell, and Illilouette Glaciers. These all converged in admirable poise
around from northeast to southeast, welded themselves together into the main
Yosemite Glacier, which, grinding gradually deeper, swept down through the
Valley, receiving small tributaries on its way from the Indian, Sentinel,
and Pohono Canons; and at length flowed out of the Valley, and on down the
range in a general westerly direction. At the time that the tributaries
mentioned above were well defined as to their boundaries, the upper portion
of the Valley walls, and the highest rocks about them, such as the Domes,
the uppermost of the Three Brothers and the Sentinel, rose above the surface
of the ice. But during the Valley's earlier history, all its rocks, however
lofty, were buried beneath a continuous sheet, which swept on above and
about them like the wind, the upper portion of the current flowing steadily,
while the lower portion went mazing and swedging down in the crooked and
dome- blocked canons toward the head of the Valley.
Every glacier of the Sierra
fluctuated in width and depth and length, and consequently in degree of
individuality, down to the latest glacial days. It must, therefore, be borne
in mind that the following description of the Yosemite glaciers applies only
to their separate condition, and to that phase of their separate condition
that they presented toward the close of the glacial period after most of
their work was finished, and all the more telling features of the Valley and
the adjacent region were brought into relief.
The comparatively level,
many-fountained Yosemite Creek Glacier was about fourteen miles in length by
four or five in width, and from five hundred to a thousand feet deep. Its
principal tributaries, drawing their sources from the northern spurs of the
Hoffman Range, at first pursued a westerly course; then, uniting with each
other, and a series of short affluents from the western rim of the basin,
the trunk thus formed swept around to the southward in a magnificent curve,
and poured its ice over the north wall of Yosemite in cascades about two
miles wide. This broad and comparatively shallow glacier formed a sort of
crawling, wrinkled ice-cloud, that gradually became more regular in shape
and river-like as it grew older. Encircling peaks began to overshadow its
highest fountains, rock islets rose here and there amid its ebbing currents,
and its picturesque banks, adorned with domes and round- backed ridges,
extended in massive grandeur down to the brink of the Yosemite walls.
In the mean time the chief
Hoffman tributaries, slowly receding to the shelter of the shadows covering
their fountains, continued to Eve and work independently, spreading soil,
deepening lake-basins and giving finishing touches to the sculpture in
general. At length these also vanished, and the whole basin is now full of
light. Forests flourish luxuriantly upon its ample moraines, lakes and
meadows shine and bloom amid its polished domes, and a thousand gardens
adorn the banks of its streams.
It is to the great width and
even slope of the Yosemite Creek Glacier that we owe the unrivaled height
and sheerness of the Yosemite Falls. For had the positions of the ice
fountains and the structure of the rocks been such as to cause
down-thrusting concentration of the Glacier as it approached the Valley,
then, instead of a high vertical fall we should have had a long slanting
cascade, which after all would perhaps have been as beautiful and
interesting, if we only had a mind to see it so.
The short, comparatively
swift-flowing Hoffman Glacier, whose fountains extend along the south slopes
of the Hoffman Range, offered a striking contrast to the one just described.
The erosive energy of the latter was diffused over a wide field of sunken,
boulder-like domes and ridges. The Hoffman Glacier, on the contrary, moved
right ahead on a comparatively even surface, making a descent of nearly five
thousand feet in five miles, steadily contracting and deepening its current,
and finally united with the Tenaya Glacier as one of its most influential
tributaries in the development and sculpture of the great Half Dome, North
Dome and the rocks adjacent to them about the head of the Valley.
The story of its death is not
unlike that of its companion already described, though the declivity of its
channel, and its uniform exposure to sun-heat prevented any considerable
portion of its current from becoming torpid, lingering only well up on the
mountain slopes to finish their sculpture and encircle them with a zone of
moraine soil for forests and gardens. Nowhere in all this wonderful region
will you find more beautiful trees and shrubs and flowers covering the
traces of ice.
The rugged Tenaya Glacier
wildly crevassed here and there above the ridges it had to cross, instead of
drawing its sources direct from the summit of the range, formed, as we have
seen, one of the outlets of the great Tuolumne Glacier, issuing from this
noble fountain like a river from a lake, two miles wide, about fourteen
miles long, and from fifteen hundred to two thousand feet deep.
In leaving the Tuolumne
region it crossed over the divide, as mentioned above, between the Tuolumne
and Tenaya basins, making an ascent of five hundred feet. Hence, after
contracting its wide current and receiving a strong affluent from the
fountains about Cathedral Peak, it poured its massive flood over the
northeastern rim of its basin in splendid cascades. Then, crushing heavily
against the Clouds' Rest Ridge, it bore down upon the Yosemite dome with
concentrated energy.
Toward the end of the ice
period, while its Hoffman companion continued to grind rock meal for coming
plants, the main trunk became torpid, and vanished, exposing wide areas of
rolling rock waves and glistening pavements, on whose channelless surface
water ran wild and free. And because the trunk vanished a!most
simultaneously throughout its whole extent, no terminal moraines are found
in its cañon channel; nor, since its walls are, in most places, too steeply
inclined to admit of the deposition of moraine matter, do we find much of
the two main laterals. The lowest of its residual glaciers lingered beneath
the shadow of the Yosemite Half Dome; others along the base of Coliseum Peak
above Lake Tenaya and along the precipitous wall extending from the lake to
the Big Tuolumne Meadows. The latter, on account of the uniformity and
continuity of their protecting shadows, formed moraines of considerable
length and regularity that are liable to be mistaken for portions of the
left lateral of the Tuolumne tributary glacier.
Spend all the time you can
spare or steal on the tracks of this grand old glacier, charmed and
enchanted by its magnificent cañon, lakes and cascades, and its resplendent
glacier pavements.
The Nevada Glacier was longer
and more symmetrical than the last, and the only one of the Merced system
whose sources extended directly back to the main summits on the axis of the
range. Its numerous fountains were ranged side by side in three series, at
an elevation of from ten to twelve thousand feet above the sea. The first,
on the right side of the basin, extended from the Matterhorn to Cathedral
Peak; that on the left through the Merced group, and these two parallel
series were united by a third that extended around the head of the basin in
a direction at right angles to the others.
The three ranges of high
peaks and ridges that supplied the snow for these fountains, together with
the Clouds' Rest Ridge, nearly inclose a rectangular basin, that was filled
with a massive sea of ice, leaving an outlet toward the west through which
flowed the main trunk glacier, three fourths of a mile to a mile and a half
wide, fifteen miles long, and from one thousand to fifteen hundred feet
deep, and entered Yosemite between the Half Dome and Mount Starr King.
Could we have visited
Yosemite Valley at this period of its history, we should have found its ice
cascades vastly more glorious than their tiny water representatives of the
present day. One of the grandest of these was formed by that portion of the
Nevada Glacier that poured over the shoulder of the Half Dome.
This glacier, as a whole,
resembled an oak, with a gnarled swelling base and wide-spreading branches.
Picturesque rocks of every conceivable form adorned its banks, among which
glided the numerous tributaries, mottled with black and red and gray
boulders, from the fountain peaks, while ever and anon, as the deliberate
centuries passed away, dome after dome raised its burnished crown above the
ice flood to enrich the slowly opening landscapes.
The principal moraines occur
in short, irregular sections along the sides of the canons, their
fragmentary conditions being due to interruptions caused by portions of the
sides of the canon walls being too steep for moraine matter to lie on, and
to down-sweeping torrents and avalanches. The left lateral of the trunk may
be traced about five miles from the mouth of the first main tributary to the
Illilouette Cañon. The corresponding section of the right lateral, extending
from Cathedral tributary to the Half Dome, is more complete because of the
more favorable character of the north side of the cañon. A short side
glacier came in against it from the slopes of Clouds' Rest; but being fully
exposed to the sun, it was melted long before the main trunk, allowing the
latter to deposit this portion of its moraine undisturbed. Some conception
of the size and appearance of this fine moraine may be gained by following
the Clouds' Rest Trail from Yosemite, which crosses it obliquely and
conducts past several sections made by streams. Slate boulders may be seen
that must have come from the Lyell group, twelve miles distant. But the bulk
of the moraine is composed of porphyritic granite derived from Feldspar and
Cathedral Valleys.
On the sides of the moraines
we find a series of terraces, indicating fluctuations in the level of the
glacier, caused by variations of snow-fall, temperature, etc., showing that
the climate of the glacial period was diversified by cycles of milder or
stormir, seasons similar to those of post-glacial time.
After the depth of the main
trunk diminished to about five hundred feet, the greater portion became
torpid, as is shown by the moraines, and lay dying in its crooked channel
like a wounded snake, maintaining for a time a feeble squirming motion in
places of exceptional depth, or where the bottom of the cañon was more
steeply inclined. The numerous fountain- wombs, however, continued fruitful
long after the trunk had vanished, giving rise to an imposing array of short
residual glaciers, extending around the rim of the general basin a distance
of nearly twenty-four miles. Most of these have but recently succumbed to
the new climate, dying in turn as determined by elevation, size, and
exposure, leaving only a few feeble survivors beneath the coolest shadows,
which are now slowly completing the sculpture of one of the noblest of the
Yosemite basins.
The comparatively shallow
glacier that at this time filled the Illilouette basin, though once far from
shallow, more resembled a lake than a river of ice, being nearly half as
wide as it was long. Its greatest length was about ten miles, and its depth
perhaps nowhere much exceeded one thousand feet. Its chief fountains, ranged
along the west side of the Merced group, at an elevation of about ten
thousand feet, gave birth to fine tributaries that flowed in a westerly
direction, and united in the center of the basin. The broad trunk at first
flowed northwestward, then curved to the northward, deflected by the lofty
wall forming its western bank, and finally united with the grand Yosemite
trunk, opposite Glacier Point.
All the phenomena relating to
glacial action in this basin are remarkably simple and orderly, on account
of the sheltered positions occupied by its ice-fountains, with reference to
the disturbing effects of larger glaciers from the axis of the main range
earlier in the period. From the eastern base of the Starr King cone you may
obtain a fine view of the principal moraines sweeping grandly out into the
middle of the basin from the shoulders of the peaks, between which the
ice-fountains lay. The right lateral of the tributary, which took its rise
between Red and Merced Mountains, measures two hundred and fifty feet in
height at its upper extremity, and displays three well-defined terraces,
similar to those of the South Lye!! Glacier. The comparative smoothness of
the uppermost terrace shows that it is considerably more ancient than the
others, many of the boulders of which it is composed having crumbled. A few
miles to the westward, this moraine has an average slope of twenty-seven
degrees, and an elevation above the bottom of the channel of six hundred and
sixty feet. Near the middle of the main basin, just where the regularly
formed medial and lateral moraines flatten out and disappear, there is a
remarkably smooth field of gravel, planted with arctostaphylos, that looks
at the distance of a mile like a delightful meadow. Stream sections show the
gravel deposit to be composed of the same material as the moraines, but
finer, and more water-worn from the action of converging torrents issuing
from the tributary glaciers after the trunk was melted. The southern
boundary of the basin is a strikingly perfect wall, gray on the top, and
white down the sides and at the base with snow, in which many a crystal
brook takes rise. The northern boundary is made up of smooth undulating
masses of gray granite, that lift here and there into beautiful domes of
which the Starr King cluster is the finest, while on the east tower the
majestic fountain peaks with wide canons and névé amphitheaters between
them, whose variegated rocks show out gloriously against the sky.
The ice ploughs of this
charming basin, ranged side by side in orderly gangs, furrowed the rocks
with admirable uniformity, producing irrigating channels for a brood of wild
streams, and abundance of rich soil adapted to every requirement of garden
and grove. No other section of the Yosemite uplands is in so perfect a state
of glacial cultivation. Its domes, and peaks, and swelling rock-waves,
however majestic in themselves, are yet submissively subordinate to the
garden center. The other basins we have been describing are combinations of
sculptured rocks, embellished with gardens and groves; the Illilouette is
one grand garden and forest, embellished with rocks, each of the five
beautiful in its own way, and all as harmoniously related as are the five
petals of a flower. After uniting in the Yosemite Valley, and expending the
down-thrusting energy derived from their combined weight and the declivity
of their channels, the grand trunk flowed on through and out of the Valley.
In effecting its exit a considerable ascent was made, traces of which may
still be seen on the abraded rocks at the lower end of the Valley, while the
direction pursued after leaving the Valley is surely indicated by the
immense lateral moraines extending from the ends of the walls at an
elevation of from fifteen hundred to eighteen hundred feet. The right
lateral moraine was disturbed by a large tributary glacier that occupied the
basin of Cascade Creek, causing considerable complication in its structure.
The left is simple in form for several miles of its length, or to the point
where a tributary came in from the southeast. But both are greatly obscured
by the forests and underbrush growing upon them, and by the denuding action
of rains and melting snows, etc. It is, therefore, the less to be wondered
at that these moraines, made up of material derived from the distant
fountain mountains, and from the Valley itself, were not sooner recognized.
The ancient glacier systems
of the Tuolumne, San Joaquin, Kern, and King's River basins were developed
on a still grander scale and are so replete with interest that the most
sketchy outline descriptions of each, with the works they have accomplished,
would fill many a volume. Therefore I can do but little more than invite
everybody who is free to go and see for himself.
The action of flowing ice,
whether in the form of river-like glaciers or broad mantles, especially the
part it played in sculpturing the earth, is as yet but little understood.
Water rivers work openly where people dwell, and so does the rain, and the
sea, thundering on all the shores of the world; and the universal ocean of
air, though invisible, speaks aloud in a thousand voices, and explains its
modes of working and its power. But glaciers, back in their white solitudes,
work apart from men, exerting their tremendous energies in silence and
darkness. Outspread, spirit-like, they brood above the predestined
landscapes, work on unwearied through immeasurable ages, until, in the
fullness of time, the mountains and valleys are brought forth, channels
furrowed for rivers, basins made for lakes and meadows, and arms of the sea,
soils spread for forests and fields; then they shrink and vanish like summer
clouds. |
