The Western United States | Page 8

their summits to view.
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.
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.
[Footnote 1: scorioe, cellular, slaggy lava.]
[Footnote 2: lapilli, volcanic ashes, consisting of small, angular, stony
fragments.]
[Illustration: FIG. 9.--PITT RIVER CAÑON, NORTHERN
CALIFORNIA
The plateau is built of layers of lava]
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.
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.

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.
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.
[Illustration: FIG. 10.--SHOSHONE FALLS, SNAKE RIVER,
IDAHO]
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