By ELIZABETH WIDEL Some tens of millions of years ago the west coast of North America
lay about where the eastern edge of Washington is now. Then as time passed -- and if
geology has anything, it's time in incomprehensible amounts - micro-continents which had
been wandering around in the Pacific Ocean one by one docked against the slowly growing
area.
The first block to join the continent was the Kootenai arc. It can be found in the
northeast corner of the state where even an amateur can see that these rocks are old and
have had a long journey. They do not appear much if any south of Spokane because there
they are overlaid by later rocks deposited on top of them by enormous floods of molten
rock welling up out of the earth's interior. If one got deep enough, they may well be
there.
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But moving in a block of real estate that huge and with those huge forces behind it is
not a simple matter. The offshore shelves with their deposits of sediments and/or
sedimentary rock get crushed and distorted in the process, and one can find some marvelous
folds in the rock as a result. |
The second addition to the area was the Okanogan micro-continent which arrived about
100 million years ago. This area, complete with volcanoes of its own from its own seacoast
and offshore ocean trench into which the ocean's crust was diving (they call this
subducting), docked against North America and then, although some sources believe it may
have been angling gently north with the floor of the Pacific Ocean, would have begun to
move west with the continent. This area now forms the highland area between the Columbia
and Okanogan rivers. And thus arrived the east half of what we call Okanogan County.
The driver going west on Highway 20 will note, the moment he crosses the Columbia not
far from Kettle Falls, the complete and abrupt change in the rocks beside the road. This
is different rock altogether.
There will be those who tell you - it is widely believed - that the Okanogan River on
the west edge of this block marks the edge of the Rocky Mountain province geologically. In
any case, the same phenomenon repeated; the offshore shelves and their strata were
elevated by the collision of the two terranes, and what had been quietly resting in the
water sometimes reappeared as mountains, deformed from the force of the encounter.
| The next accretion was the North Cascades micro-continent, which also, with an
off-shore trench, had its own set of volcanoes. The forces which operate on land forms and
mountains and all that surrounds them continued and the North Cascades have a colorful
story of their own. The mountains seen today are at least the second range to occupy that
area, the first set running more north-south than the present ones. And thus arrived the
west half of the county.
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But deep in the earth where sediments had been collected and other kinds of rock mixed
in, the earth forces compressed and folded and these rocks with new solutions until, even
though they may not have melted, the rocks softened to the point where their minerals
recrystalized, their chemistry was altered, and the rock gneiss was produced, a rock made
deep underground under considerable earth agony. |
| Then, as the Cascades continued to rise - some say at the rate of about an inch a year
- the overlying rock was eroded away and the gneiss was exposed. It is called the core of
the Cascade Range. There is a large deposit of it in the Okanogan Highlands, too, along
with the roots of some volcanoes there - and lots of granite. |
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The Cascades province also has a variety of other kinds of rocks around the edges,
lots of one called grano-diorite which has a golden tint to it and which makes for some
magnificent peaks, and others. And as if the stress of orogony which produced the gneiss
weren't enough, there also is some dramatic overthrusting where whole mountains were
shoved from one place to another, producing the anomaly of older rock lying on top of
younger, something not usually done.
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The last pieces of terrane added were the coastal areas, largely made up of oceanic
rock. With the mapping and satellite imaging of these days, it is not likely that we will
acquire any more terranes - unless geology produces something which presently is under
water, though there is quite a bit of that.
Some 17 million or so years ago there is evidence that the earth was struck by an
asteroid, not the first time, and as on the other occasions, it was as if the earth, given
such a blow and wound, bled as a result. What it bled was molten basalt. This last one is
believed to have struck near the southeast corner of Oregon, and the resultant seams which
opened up and poured forth liquid basalt covered thousands of square miles of area: most
of southeastern Washington, parts of eastern Oregon, with bits and pieces found in Idaho,
northern California and even a bit in Nevada.
| There is a pie-shaped piece of it on the south boundary of Okanogan County. For some
reason the Columbia River made a shortcut across the basalt - the only place it does so -
and cut itself a channel through the heavy rock running from Goose Flats to Brewster.
Everywhere else it goes around the edge of the basalt plateau. In its abandoned channel
lies Omak Lake, eight or nine miles long and said to be 350 feet deep, the result of what
is termed overdeepening by the glacier.
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For the evolution of the area had not finished even then. Glaciation made its
appearance as the global climate changed, and continental ice sheets which originated in
Canada and moved south were so driven by climate and ice formation that they flowed up
over the mountains as they came south, disarranging the angles of many of the Cascades'
streams. There was alpine glaciation, too, where glaciers formed on high mountains and
then reamed their way down the valleys, leaving their telltale marks of flat-bottomed,
U-shaped valleys, sharp cliffs, hanging valleys which produced waterfalls, and a
distribution of many kinds of rock which were imported, not native to the area.
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| The signature of the ice lies everywhere in this area, from deposits of rock and
gravel which are unsorted and tumbled in all together, small hills (kames) which seem to
be where they are for no reason at all, winding ridges (eskers) which dropped out of the
glaciers when they began to melt, valleys like the Methow and the Okanogan which were
reamed out to their present shape. It is said that the ice came earlier, flowed deeper and
stayed longer in the Okanogan than the Methow because it had a straight shot down a
pre-existing valley and did not have to climb mountains as it did in the Methow, to get
where it was going. From the runoff which followed the thaw came great layered deposits,
those with heavier rocks indicating spring runoff grading down to the silt of winter.
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There are scratches in the rocks in high places, and rounded and smoothed faces on
rocks in many places, all the signature of ice. And when the climate moderated and the
overload of ice began to melt, there were subsidiary valleys carved in many places as the
water began its rush to the sea while the main valleys still were plugged.
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There are those who claim that the most important deposits in Washington are neither
gold nor silver but gravel, the gift of the glaciers. For when the thaw-off came and the
masses of ice lost their power, they laid down their loads right where they stood. There
were enormous lakes all over the place, and the old shorelines can be seen on many a
hillside. The Okanogan Valley is known for its glacial benches, deposits of the dying ice.
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Another phenomenon which left its signature on the area was the formation and draining
of Glacial Lake Missoula. During the ice ages a tongue of the continental glacier dammed
the Clark Fork Valley east of Spokane, and the water backed up behind it far into Idaho
and Montana. When the dam failed, a flood of monster proportions was turned loose. It
raced across the basalt plateau, tearing and carving as it went and leaving swarms of
coulees behind it.
Basalt is a hard, dense rock, but it is jointed into columns, and the water got into
those cracks and did what is called plucking, tearing out hunks of the rock. Thunderous
waterfalls developed in many places, and the pounding, tearing water carved out the
jointed rock and left channels, some of them huge, behind. The formation and failure of
the ice dam is thought to have happened many times (at least 41 shorelines have been
counted), with the result that many of the coulees are sizeable. Two of the most dramatic
are the Grand Coulee and the Lower Coulee. Another huge one, Moses Coulee, is south of
Wenatchee.
| The Grand Coulee became a piece in the economy of the region when it was turned into a
holding reservoir for water to be used in a huge irrigation system. Dammed at both ends
and with a system of pumps to lift the water to it from the Columbia, Banks Lake in the
upper coulee holds a part of the lifeblood - water - of the region.
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Although Mt. St. Helens' eruption in 1980 made headlines coast to coast, it was not the
first time that this - or other - volcanoes had sounded off here, for the soil is decayed
volcanic ash and very fertile. Seed it and water it and it will produce handsomely. And
there are places where one can find a white stripe which is identified as volcanic ash
laid down by other, earlier eruptions of St. Helens, which presently is considered the
most active volcano in the Cascades, certainly in the state.
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The rise of the Cascades, as indicated still rising, has affected the climate, for
they cut off the moisture which is enjoyed by people on the coast. As the winds are forced
upward by the mountains into cooler air, they lose their load of moisture, and the
rainfall on the west side of the mountains is substantially higher than in Okanogan
County, said, variously, to be between 10 and 17 inches a year. According to official
definition, desert is an area with five inches or less of rainfall. Irrigation, therefore,
is a necessity here.
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| Like many new ideas, even scientific ones, Alfred Wegner's theory of continental
drift, also known as plate techtonics, was not accepted as soon as it was proposed. He did
not live to see its acceptance, for although he propounded it in 1912 and published a book
on it in 1920, he died in 1930.
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Other scientists became interested - both for and against - and it was not until after
extensive mapping of the ocean basins, helped out by World War II, that the theory began
to get any acceptance.
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Today, as a result of continued study, matching of fossils from both sides of the
Atlantic, checking of the magnetism of the rocks on both sides of the mid-ocean rifts and
much other detective study, the plate techtonics theory is pretty well accepted. The
continents, riding on great slabs of lighter rock (granite), float on a sub-stratum of
heavier oceanic rock (basalt), and incomprehensible forces in the earth's interior keep
things moving. North America moves west at a rate of about two inches a year. |
In the plate techtonics process, a 46,000-mile-long rift in the oceans winds around the
earth much like the seam on a baseball. Since the circumference of the globe is only about
25,000 miles, the mid-ocean rift, as it is called, obviously does some wandering. It hits
all the oceans.
In the depths of this rift the earth, termed "this hot-hearted planet on which we
ride," spews out molten basaltic magma, a confrontation of gigantic forces, for at
the depths of the rift, oceanic pressure is said to be two tons per square inch, and what
can move rock against such a force must itself be a tremendous force.
This extruded rock slowly moves from the rift valley toward the continents on both
sides and proceeds like a conveyor belt toward the those continents. The age of the sea
floor gets progressively older as it gets closer to the continents. And since it has to
have somewhere to go when it gets there, it dives down under the continental granite and
slowly makes its way back into the interior of the earth - the subduction process.
Since the granite is lighter than the basalt, the granite rafts on which the continents
are seated always ride over the heavier rock. They float. And the heavier stuff goes back
down to the interior layers of the earth, the asthenosphere and the mantle, and ultimately
melts, releasing all the water and minerals it contains. The inevitable result of this is
the formation of an arc of mountains - volcanic mountains - some miles inland from the
edge of the continent.
The lands which once had migrated to what is now the South Pole and concentrated there
roughly 245 million years ago gradually migrated away from that center. The mass which
became theAmerican continents pulled away from Africa-Europe, leaving a tell-tale outline
which shows where South America andAfrica once nested together.
Other bits of terrane from the moving continents and broken-up bits of earlier
continents were moving about in what is now the Pacific Ocean. The NorthAmericanContinent,
which we would have found unrecognizable several hundred millionyears ago, gradually
accumulated a number of these as they suytured themselves to the landmass slowly moving
westward.
This theory was explained by two men who teach at the University of Montana, David
D.Alt and Donald W. Hyndman, though it also can be found in the book Exploring Our Living
Planet, by Robert D. Ballard, published by the Natinal Geographic Society. Alt and
Hyndman's earlier book is Roadside Geology ofWashington.
For further information in this field, try Cascadia by Bates McKee, a book very well
written in language the non-professional can understand but containing information now
superceded by more recent research, as well as the two quoted above. See also the article
in the May 1998 National Geographic entitled "Cascadia: Walking on Fire," which
details the forces of volcanoes, earthquakes and faults in the earth's crust and their
effects.As always, withg anything the Geographic does, the photography is magnificent.
Finally, a new (1995) book by Alt and Hyndman, Northwest Exposures, A Geologic Story of
the Northwest goes into much more detail than the Roadside book but always in lucid,
non-professional language. |
