Chapter 11
The Ancient Yosemite Glaciers:
How the Valley Was Formed
Part 3
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
10,000
to 12,000 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 1000 to 1500 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 cañons, their fragmentary condition being due to
interruptions
caused by portions of the sides of the cañon 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 stormier 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 1000 feet. Its chief fountains, ranged along the west side of
the Merced group, at an elevation of about 10,000 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 poured 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 Lyell Glacier. The comparative
smoothness of the upper-most 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 of the
majestic fountain-peaks with wide cañons and neve amphitheaters
between
them, whose variegated rocks show out gloriously against the sky.
The ice-plows 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, and 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 1500 to 1800 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
Kings 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.
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