American Falls press. [volume] (American Falls, Idaho) 1907-1937, 1916-04-27
THE SNAKE RIVER PLAINS.

This Is the name given by the
United States Geological Survey to
that broad expanse of comparatively
level country that extends almost COM
pletely across southern Idaho.
On the north 1t is bounded by high
mountains. The southern boundary is
not SO well defined as the mountains
there are in the form Of ranges with
valleys between. The area of this
series of plains is about 35, 900 square
miles. 1t has been known as the
Snake River Desert but this Is a mis-
homer. Although some portions are
~lava-covered and desert in character,
there are thousands of square miles
OF excellent soil, needing only water
to make It splendid agricultural land.
The geological history of these
plains is somewhat as follows: Many
ages ago there was a large depres-
sion formed in the mountains that
occupied the southern part OF the
state. This depression was caused
either by a big fold or by the settling
down of an enormous rock mass over
what is today the Snake River Plains.
This old depression, which was evil
IDENTIFY occupied by a big stream prob
ably larger than the Snake River, was
deeper than the present plains with
respect to the mountains.
Across the western end Of this de-
preston a rise Of the earth's crust
took place which damned the stream
occupying the valley and caused the
formation Of a great lake that ex-
tended from Oregon almost to the
Teton mountains. This lake was
named by the biologists Payette
lake, though II had no connection with
the present Payette lake. II extend
ed up the Boise river to an elevation
which is now 1920 feet above sea
level and into this lake were carried
sand and other sediments forming
sandstone rock, and In some places
thin seams of coal from the growth
of timber along the swampy edges OF
the lake.
In the course Of time the outlet
river began to gradually drain this
lake, but while this was going on this
part OF the country became the seat
Of tremendous volcanic activity
which continued up TO very recent
times. Along the shores OF the lake
I volcanoes broke forth and evidently
assures opened in the floor OF the lake
itself and sheets Of lava we're poured
ont over the bottom OF the lake. These
lava outbursts were evidently periodic
as layers OF sand occur between the
sheets Of lava IN many places, repre-.
senting periods without volcanic ac.
tivity. These flows of lava complete.
ly covered the lake beds in the eastern
| end Of the plains but In the western
part there are numerous exposures.
The combination OF the draining by
the outlet stream and the filling in
by sediments and lava flows event,
ually caused the lake to dry up and
the Snake river began to cut III
channel up the valley. through tn.
lava and lake beds, forming the deeJ
canyon and numerous waterfalls tina
row exist, and this process Of cut
ing back is still going on. though /
Is imperceptible except by careful
measurement.
The streams from the north In tn
eas-ern part OF he plains sink through
the lara and find their way TO til.
Snake in the form Of large springs. II
the course Of centuries these stream
will grade up their channels, formini
a bed ~impervious to the water an'
will reach the Snake Just as those o,