The Western Cordillera
A similar but greater contrast separates the mountains of eastern North
America and those of the western cordillera--the fourth and last of the
main physical divisions of the continent. In both the
Laurentian and the
Appalachian highlands
the eastern mountains show no trace of the original forms produced by the
faulting of the crust or by volcanic movements. All the original
distinctive topography has been removed. What we see today is the product
of erosion working upon rocks that were thousands of feet beneath the
surface when they were brought to their present positions. In the western
cordillera, on the contrary, although much of the present form of the land
is due to erosion, a vast amount is due directly to so-called "tectonic"
activities such as the breaking of the crust, the pouring out of molten
lavas, and the bursting forth of explosive eruptions.
The character of these tectonic activities has differed widely in
different parts of the cordillera. A broad upheaval of great blocks of the
earth's crust without tilting or disturbance has produced the plateaus of
Arizona and Utah. The gorges that have been rapidly cut into such great
upheaved blocks form part of the world's most striking scenery. The Grand
Canyon of the Colorado with its tremendous platforms, mesas, and
awe-inspiring cliffs could have been formed in no other way. Equally
wonderful are some of the narrow canyons in the broadly upheaved plateaus
of southern Utah where the tributaries of the Virgin and other rivers have
cut red or white chasms thousands of feet deep and so narrow that at their
bottoms perpetual twilight reigns. It is a curious proof of the
fallibility of human judgment that these great gorges are often cited as
the most striking examples of the power of erosion. Wonderful as these
gorges certainly are, the Piedmont plain or the northwestern peneplain is
far more wonderful. Those regions had their grand canyons once upon a
time, but now erosion has gone so far that it has reduced the whole area
to the level of the bottoms of the gorges. Though such a fate is in store
for all the marvelous scenery of the western cordillera, we have it, for
the present at least, as one of the most stimulating panoramas of our
American environment. No man worthy of the name can sit on the brink of a
great canyon or gaze up from the dark depths of a gorge without a sense of
awe and wonder. There, as in few other places, Nature shows with
unmistakable grandeur the marvelous power and certainty with which her
laws work out the destiny of the universe.
In other parts of the great American cordillera some of the simplest
and youngest mountain ridges in the world are found. In southern Oregon,
for example, lava blocks have been broken and uplifted and now stand with
steep fresh faces on one side and with the old surface inclining more
gently on the other. Tilted blocks on a larger scale and much more deeply
carved by erosion are found in the lofty St. Elias Mountain of Alaska,
where much of the erosion has been done by some of the world's greatest
glaciers. The western slope of the Wasatch Mountains facing the desert of
Utah is the wall of a huge fracture, as is the eastern face of the Sierra
Nevadas facing the deserts of Nevada. Each of these great faces has been
deeply eroded. At the base, however, recent breaking and upheaval of the
crust have given rise to fresh uneroded slopes. Some take the form of
triangular facets, where a series of ridges has been sliced across and
lifted up by a great fault. Others assume the shape of terraces which
sometimes continue along the base of the mountains for scores of miles. In
places they seem like bluffs cut by an ancient lake, but suddenly they
change their altitude or pass from one drainage area to another as no
lake-formed strand could possibly do.
In other parts of the cordillera, mountains have been formed by a
single arching of the crust without any breaking. Such is the case in the
Uinta Mountains of northwestern Utah and in some of the ranges of the
Rocky Mountains in Colorado. The Black Hills of South Dakota, although
lying out in the plains, are an example of the same kind of structure and
really belong to the cordillera. In them the layers of the earth's crust
have been bent up in the form of a great dome. The dome structure, to be
sure, has now been largely destroyed, for erosion has long been active.
The result is that the harder strata form a series of concentric ridges,
while between them are ring-shaped valleys, one of which is so level and
unbroken that it is known to the Indians as the "race-course." In other
parts of the cordillera great masses of rock have been pushed horizontally
upon the tops of others. In Montana, for example, the strata of the plains
have been bent down and overridden by those of the mountains. These are
only a few of the countless forms of breaking, faulting, and crumpling
which have given to the cordillera an almost infinite variety of scenery.
The work of mountain building is still active in the western
cordillera, as is evident from such an event as the San Francisco
earthquake. In the Owens Valley region in southern California the gravelly
beaches of old lakes are rent by fissures made within a few years by
earthquakes. In other places fresh terraces on the sides of the valley
mark the lines of recent earth movements, while newly formed lakes lie in
troughs at their base. These Owens Valley movements of the crust are parts
of the stupendous uplift which has raised the Sierra Nevada to heights of
over 14,000 feet a few miles to the west. Along the fault line at the base
of the mountains there runs for over 9.50 miles the world's longest
aqueduct, which was built to relieve Los Angeles from the danger of
drought. It is a strange irony of fate that so delicate and so vital an
artery of civilization should be forced to lie where a renewal of
earthquake movements may break it at any time. Yet there was no other
place to put it, for in spite of man's growing control of nature he was
forced to follow the topography of the region in which he lived and
labored.
Volcanoes as well as earth movements have occurred on a grand scale
within a few hundred years in the cordillera. Even where there is today no
visible volcanic activity, recent eruptions have left traces as fresh as
if they had occurred but yesterday. On the borders of the Grand Canyon of
the Colorado one can see not only fresh cones of volcanic ash but lava
which has poured over the edges of the cliffs and hardened while in the
act of flowing. From Orizaba and Popocatepetl in Mexico through Mount San
Francisco in Arizona, Lassen Peak and Mount Shasta in California, Mount
Rainier with its glaciers in the Cascade Range of Washington, and Mount
Wrangell in Alaska, the cordillera contains an almost unbroken chain of
great volcanoes. All are either active at present or have been active
within very recent times. In 1912
Mount Katmai, near the northwestern end of the volcanic chain, erupted
so violently that it sent dust around the whole world. The presence of the
dust caused brilliant sunsets second only to those due to
Krakatoa in 1883. It also cut off so much sunlight that the effect was
felt in measurements made by the Smithsonian Institution in the French
provinces of North Africa. In earlier times, throughout the length of the
cordillera great masses of volcanic material were poured out to form high
plateaus like those of southern Mexico or of the Columbia River in Oregon.
In Utah some of these have been lifted up so that heavy caps of lava now
form isolated sheets topping lofty plateaus. There the lowland shepherds
drive their sheep in summer and live in absolute isolation for months at a
time. There, as everywhere, the cordillera bears the marks of mountains in
the making, while the mountains of eastern America bear the marks of those
that were made when the world was young.
The geysers and hot springs of the Yellowstone are another proof of
recent volcanic activity. They owe their existence to hot rocks which lie
only a little way below the surface and which not long ago were molten
lava. The terraces and platforms built by the geysers are another evidence
that the cordillera is a region where the surface of the earth is still
being shaped into new forms by forces acting from within. The physical
features of the country are still in process of construction.
In spite of the importance of the constructive forces which are
still building up the mountains, much of the finest scenery of the
cordillera is due to the destructive forces of erosion. The majestic
Columbia Canyon, like others of its kind, is the work of running water.
Glaciers also have done their part. During the glacial period the forces
which control the paths of storms did not give to the cordillera region
such an abundance of snow as was sifted down upon Laurentia. Therefore no
such huge continental glaciers have flowed out over millions of square
miles of lower country. Nevertheless among the mountains themselves the
ice gouged and scraped and smoothed and at its lower edges deposited great
moraines. Its work today makes the cliffs and falls of the Yosemite one of
the world's most famous bits of scenery. This scenery is young and its
beauty will pass in a short time as geology counts the years, for in
natural scenery as in human life it is youth that makes beauty. The
canyons, waterfalls, and geysers of the cordillera share their youth with
the lakes, waterfalls, and rapids due to recent glaciation in the east.
Nevertheless, though youth is the condition of most striking beauty,
maturity and old age are the condition of greatest usefulness. The young
cordillera with its mountains still in the making can support only a
scanty population, whereas the old eastern mountains, with the lines of
long life engraved upon every feature, open their arms to man and let him
live and prosper.
It is not enough that we should picture merely the four divisions of
the land of our continent. We must see how the land meets the sea. In low
latitudes in both the Old World and the New, the continents have tended to
emerge farther and farther from the sea during recent geological times.
Hence on the eastern side of both North and South America from New Jersey
to Brazil the ocean is bordered for the most part by coastal plains,
uplifted from the sea only a short time ago. On the mountainous western
side of both continents, however, the sea bottom shelves downward so
steeply that its emergence does not give rise to a plain but merely to a
steep slope on which lie a series of old beaches several hundred and even
one thousand feet above the present shore line. Such conditions are not
favorable to human progress. The coastal plains produced by uplift of the
land may be fertile and may furnish happy homes for man, but they do not
permit ready access to the sea because they have no harbors. The chief
harbor of Mexico at Vera Cruz is merely a little nick in the coast-line
and could never protect a great fleet, even with the help of its
breakwater. Where an enterprising city like Los Angeles lies on the
uplifted Pacific coast, it must spend millions in wresting a harbor from
the very jaws of the sea.
In high latitudes in all parts of the world the land has recently
been submerged beneath the sea. In some places, especially those like the
coasts of Virginia and central California which lie in middle latitudes, a
recent slight submergence has succeeded a previous large emergence.
Wherever such sinking of the land has taken place, it has given rise to
countless bays, gulfs, capes, islands, and fiords. The ocean water has
entered the valleys and has drowned their lower parts. It has surrounded
the bases of hills and left them as islands; it has covered low valleys
and has created long sounds where traffic may pass with safety even in
great storms. Though much land has thus been lost which would be good for
agriculture, commerce has been wonderfully stimulated. Through Long Island
Sound there pass each day hundreds of boats which again and again would
suffer distress and loss if they were not protected from the open sea. It
is no accident that of the eight largest metropolitan districts in the
United States five have grown up on the shores of deep inlets which are
due to the drowning of valleys.
Nor must the value of scenery be forgotten in a survey such as this.
Year by year we are learning that in this restless, strenuous American
life of ours vacations are essential. We are learning, too, that the love
of beauty is one of Nature's greatest healers. Regions like the coast of
Maine and Puget Sound, where rugged land and life-giving ocean interlock,
are worth untold millions because of their inspiring beauty. It is indeed
marvelous that in the latitude of the northern United States and southern
Canada so many circumstances favorable to human happiness are combined.
Fertile soil, level plains, easy passage across the mountains, coal, iron,
and other metals imbedded in the rocks, and a stimulating climate, all
shower their blessings upon man. And with all these blessings goes the
advantage of a coast which welcomes the mariner and brings the stimulus of
foreign lands, while at the same time it affords rest and inspiration to
the toilers here at home.
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