<h2><SPAN name="page_019">HOW THE COLUMBIA PLATEAU WAS MADE</SPAN></h2>
<p class="indent">
Years ago people disputed as to the way in which the earth was made.
Those who lived where all the rocks had, like lava, the appearance
of having once been melted, believed that fire had done all the
work. Those who lived where the rocks appeared to be formed of
hardened mud, sand, and lime, substances such as we find accumulating
under water, said that water alone had been the means. But in later
years the earth's surface has been more widely explored, and now
it is known that both opinions were partly right. Water and fire
have both been concerned in the making of the earth.</p>
<p class="indent">
In the great valleys fire-formed rocks are rare, but they are more
or less abundant in all mountainous regions, for where mountains
are, there the crust of the earth is weakest. There are many reasons
for believing that the interior of the earth is very hot. We know
that the surface is settling in some places and rising in others,
and that where the strain of the upheaval is too great the rocks are
broken. These convulsions sometimes cause earthquakes and sometimes
volcanic eruptions, when enormous quantities of molten rock are
poured out over the surface. In all the long history of our earth
probably no greater flood of lava than that which made the Columbia
plateau was ever spread over the surface of any region. Travel where
you will over the plains of southern Idaho, central Washington,
or Oregon, and examine the rocks which here and there rise above
the soil or are exposed in the cañons, and you will find
that they all appear to have been formed by fire.</p>
<div class="img_ctr" style="width: 511px;">
<ANTIMG src="images/fig007.jpg" width-obs="511" height-obs="366" alt="Fig. 7">
FIG. 7.—SNAKE RIVER AT IDAHO FALLS
<p class="imgnote">Just beginning to cut a cañon in the
volcanic plateau</p>
</div>
<p class="indent">
These rocks are dark in color and very hard. They are not arranged
in regular layers like sandstone and shale; many of them show numerous
little cavities which once contained steam. These cavities give
to the rock a slag-like appearance. In this kind of rock, which
we shall call lava, there are, of course, no remains of shells
or bones of animals such as are often found in rocks formed from
sand or clay.</p>
<p class="indent">
Do not picture to yourself the Columbia plateau as one continuous
stretch of level land, for it is broken by many mountain ranges.
Some of these are old mountains which were too tall to be buried
by the lava, but most of them have been formed out of the plateau
itself. The eruptions which made the plateau extended through a
very long time, perhaps hundreds of thousands of years, and the
older lava is deeply decayed and covered with soil. Some of the
later flows show extremely rough and rugged surfaces and are probably
only a few hundred years old.</p>
<div class="img_ctr" style="width: 511px;">
<ANTIMG src="images/map001.jpg" width-obs="511" height-obs="512" alt="Map 1">
MAP OF THE COLUMBIA PLATEAU</div>
<p class="indent">
Long ago, before the eruptions began, the geography of the Northwest
was very different from what it is now. Instead of a vast plateau
there were mountains and valleys. Lowlands occupied most of the
region where the Cascade Range now rises with its lofty volcanic
peaks. Portions of the basin of the present Columbia River were
occupied by lakes which extended southwest into California.</p>
<p class="indent">
Movements of the earth began to affect the region of the present
plateau, and at many points the solid rocks were fissured and broken.
Then from that mysterious region far beneath the surface came steam
and gases, escaping through the fissures with explosive force.
In some places cinder cones were built about the openings by the
fragments of lava which were hurled out. In other places, during
periods of less explosive eruption, molten lava flowed out in vast
quantities. The lava was very hot and almost as liquid as water,
so that it spread in thin sheets over hundreds of square miles
of lowland.</p>
<p class="indent">
One important series of fissures through which eruptions took place
marked the line where the Cascade Range was to be built. Other
volcanoes appeared over the surface of southern Idaho, central
Washington, Oregon, and northeastern California.</p>
<p class="indent">
The eruptions were not continuous over the whole field; now in
this place, now in that, there came long periods of quiet. During
such periods the earthquakes ceased, the lava became cold, and
the clouds of volcanic ashes cleared from the air. Frequently the
lava intercepted streams and blocked the valleys so that large
lakes were formed. Whenever the periods of quiet were very long,
plants spread over the surface and animals of many kinds made their
homes about the lakes.</p>
<p class="indent">
In eastern Oregon the John Day River and its branches have eroded
cañons through the later lava and have exposed the sands,
clays, and gravels which collected at the bottom of one of those
ancient lakes. In these beds the skeletons of many strange and
interesting animals have been found. Evidently they had once lived
about the borders of the lake, and the streams had washed their
bones into the water and mingled them with the sediment.</p>
<div class="img_ctr" style="width: 513px;">
<ANTIMG src="images/fig008.jpg" width-obs="513" height-obs="362" alt="Fig. 8">
FIG. 8.—BLUE LAKES, IDAHO
<p class="imgnote">Formed by springs issuing from underneath
the lava of the plateau</p>
</div>
<p class="indent">
One of these animals appears to have been an ancestor of the present
horse. It was about the size of a sheep, and had three toes instead
of one. Another, probably a very dangerous animal, was related to
our present hog, but stood nearly seven feet high. Others resembled
the rhinoceros, camel, tapir, or peccary. All but the peccary are
now extinct upon this continent. Of the carnivorous animals there
were wolves and cats of large size.</p>
<p class="indent">
The eruptions continued, filling the valleys little by little,
until in places the lava reached a thickness of nearly four thousand
feet. The lower mountains were hidden from sight. We know of the
existence of these buried mountains because the wearing away of
the lava in some places has exposed their summits to view.</p>
<p class="indent">
The lava flood reached farther and farther. In southern Idaho it
formed the Snake River plains, which must have been, when first
formed, hundreds of miles long, seventy-five miles wide, and almost
as even as a floor. If we could have looked on while these things
were taking place it would have appeared as if the whole land was
about to sink under the fiery mass which flowed out of the earth.
The streams and valleys were completely buried. The region of the
John Day Lake, with all its animal remains, was covered. The lava,
like a sea, crept up against the mountains surrounding the plateau
region. Bays of lava extended into the valleys among the mountains,
while mountain ridges rose like islands and capes from the surface
of the flood.</p>
<p class="indent">
We never tire of looking at the lofty snow-capped peaks of the
Cascade Range. A dozen of them rise over ten thousand feet, and
two, Mounts Shasta and Ranier, are more than fourteen thousand
feet high. All these mountains were formed of material thrown out
of the interior of the earth during the building of the Columbia
plateau. The process was very similar for each. About some one
exceptionally active crater immense quantities of scoriæ[1]
and lapilli[2] accumulated. Then came streams of fiery lava, some
of which, hardening upon the outer slopes of the crater, added
still more to the growth of the mountain. The process was very
slow, however. A time of eruption, marked by tremblings of the
earth, explosive noises, and a sky filled with dust and clouds,
might last for many years. Then came a long period of rest when
the falling rains, gathering in dashing torrents, cut deep gullies
down the sides of the mountain.</p>
<p class="footnote">
[Footnote 1: <i>scori&oelig;</i>, cellular, slaggy lava.]</p>
<p class="footnote">
[Footnote 2: <i>lapilli</i>, volcanic ashes, consisting of small,
angular, stony fragments.]</p>
<div class="img_ctr" style="width: 513px;">
<ANTIMG src="images/fig009.jpg" width-obs="513" height-obs="388" alt="Fig. 9">
FIG. 9.—PITT RIVER CAÑON, NORTHERN CALIFORNIA
<p class="imgnote">The plateau is built of layers of lava</p>
</div>
<p class="indent">
The volcanoes at last ceased to grow any higher, for the lava,
if the eruptions continued, formed new craters at their bases.
It is probable that all these great peaks have been extinct for
several thousand years, although some are much older and more worn
away than others. One of these volcanoes has completely disappeared,
and in its place lies that wonderful sheet of water known as Crater
Lake. It is thought that the interior of this mountain was melted
away during a period of activity, and that the outer portion fell
in, leaving a crater five miles across and nearly a mile deep.</p>
<p class="indent">
The streams of lava, as they flowed here and there building up
the plateau, frequently broke up the rivers and turned them into
new channels. As time went on the eruptions were less violent, and
the rivers became established in the channels which they occupy
to-day. The Columbia River, winding about over the plateau, sought
the easiest path to the sea. It soon began to dig a channel, and
now has hidden itself between dark walls of lava.</p>
<p class="indent">
But other forces besides the streams were now at work in this volcanic
region. The lava plateau began slowly to bend upward along the
line of the great volcanoes, lifting them upward with it. In this
manner the Cascade Range was formed. The Columbia River, instead
of seeking another way to the sea, continued cutting its channel
deeper and deeper into the growing mountain range, and so has given
us that picturesque cañon which forms a most convenient
highway from the interior of Washington and Oregon to the coast.</p>
<p class="indent">
Take a sheet of writing paper, lay it upon an even surface, then
slowly push the opposite edges toward each other. This simple experiment
will aid one in understanding one of the ways in which mountain
ranges are made. Besides the upward fold of the plateau which made
the Cascade Range, another was formed between the Blue Mountains
in eastern Oregon and a spur of the Rocky Mountains in northern
Idaho. This fold lay across the path of the Snake River, but its
movement was so slow that the river kept its former channel and in
this rising land excavated a cañon which to-day is more than
a mile deep. The upper twenty-five hundred feet of the cañon
are cut into the lava of the plateau, and the lower three thousand
into the underlying granite. The cañon is not so picturesque
as the Colorado, for it has no rocks with variegated coloring or
castellated walls. Its sides are, however, exceedingly precipitous
and it is difficult to enter.</p>
<div class="img_ctr" style="width: 516px;">
<ANTIMG src="images/fig010.jpg" width-obs="516" height-obs="375" alt="Fig. 10">
FIG. 10.—SHOSHONE FALLS, SNAKE RIVER, IDAHO</div>
<p class="indent">
Along portions of the lower Columbia and Snake rivers, navigation
is obstructed by rapids and waterfalls. The presence of these falls
teaches us that these streams are still at work cutting their channels
deeper. The Snake River in its upper course has as yet cut only a
very shallow channel in the hard lava, and the beautiful Shoshone
Falls marks a point where its work is slow. These falls, which
are the finest in the northwest, owe their existence to the fact
that at this particular spot layers of strong resistant lava cover
the softer rocks.</p>
<p class="indent">
There are other cañons in the plateau region which are fully
as remarkable as those which have been mentioned. That of the Des
Chutes River in central Oregon is in places a thousand feet deep,
with almost vertical walls of lava.</p>
<p class="indent">
We have already seen how mountains have been formed upon the Columbia
plateau, by a bending of the earth upward. Other mountains of the
plateau are due to fractures in the solid rocks, often many miles
long. Upon one side of these fractures the surface has been depressed,
while upon the other it has been raised. The amount of the uplift
varies from a few hundred to thousands of feet. The mountains thus
formed have a long, gentle slope upon one side and a very steep
incline upon the other. They are known as "block mountains," and
those upon the Columbia plateau are the most interesting of their
kind in the world.</p>
<p class="indent">
With the exception of a few large rivers, the greater portion of the
Columbia plateau is remarkable for its lack of surface streams. The
water which reaches the borders of the plateau from the surrounding
mountains often sinks into the gravel between the layers of lava
and forms underground rivers. The deep cañons which have
been mentioned intercept some of these underground rivers, so that
their waters pour out and down over the sides of the cañons
in foaming cascades. The greatest of these cascades is that known as
the Thousand Springs in the Snake River cañon. The waters of
the Blue Lakes in the cañon of the same river below Shoshone
Falls also come from underneath the lava. They are utilized in
irrigating the most picturesque fruit ranch in southern Idaho.</p>
<div class="img_ctr" style="width: 522px;">
<ANTIMG src="images/fig011.jpg" width-obs="522" height-obs="745" alt="Fig. 11">
FIG. 11.—CAÑON OF CROOKED RIVER NEAR THE DES CHUTES RIVER
<p class="imgnote">Eroded in the Columbia plateau</p>
</div>
<p class="indent">
The climate of the plateau is dry, and its eastern portion is
practically a desert. Toward the west, however, the rainfall is
greater, and in central Washington and northern Oregon the plateau
becomes one vast grain-field. It is difficult to irrigate the plateau
because the streams flow in such deep cañons, but above
the point where the cañon of the Snake River begins there
is an extensive system of canals and cultivated fields. With a
sufficient water supply, the lava makes one of the richest and
most productive of soils. Along the Snake and Columbia rivers,
wherever there is a bit of bottom land, orchards have been planted.
Little steamers ply along these rivers between the rapids, gathering
the fruit and delivering it at the nearest railroad point.</p>
<p class="indent">
Mining is carried on only in the mountains which rise above the
lava flood, for the mineral veins are for the most part older than
the lava of the plateau. We are certain that many very valuable
deposits of the precious metals lie buried beneath the lava fields.</p>
<p class="indent">
It is thought that the volcanic history of the Columbia plateau
has been completed. Now the streams are at work carrying away the
materials of which it is composed and may in time uncover the old
buried land surface.</p>
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