THE LAST 13 MILLION
YEARS
We
continue our story of Silver Falls State Park between 13 and 9 million years
ago when a volcanic explosion laid down a 1,500 feet thick blanket of ash,
pumice, and rock fragments. These pyroclastic materials quickly fused together
to create a welded tuff, known as the Fern Ridge Tuff. It is still found today
in many upland areas such as Fern Ridge, located between Silver Falls State
Park and the North Santiam River to the south. The reason why you won’t easily
see it in the park is because it is easily erodible. The hills in the
southwestern portion of this park are capped with this rock and have not been
completely eroded away. There is two roadcuts on State Highway 214 just over 2
miles west of the park campgrounds; they stand out as a buff white to pinkish-white
rock. Ever since this layer of welded tuff was created over 9 million years
ago, it has been eroding into hard clay.
A
layer of soil began to grow whenever the rocks were eroded to a slope suitable
for accumulation of sediments and organic material. Water Percolated through
the basalt, and where the casts of trees were encountered, minerals were
deposited. These minerals include manganese, silica, and iron. As the
waterfalls and ice eroded the soft layers of sand between the Grand Ronde Flows
and the Wanapum flows, the casts of trees were exposed, and in the case of
South Falls, these casts were eroded into gaping holes. These holes are known
as erosional chimneys. The dark red soils of the nearby Salem Hills where the
Willamette Valley Vineyards are located would be what the soil in Silver Falls
State Park would look like if the grass was taken out.
The Creation of the
Waterfalls
This
park embraces the greatest concentration waterfalls in Oregon, even beating out
the Columbia River Gorge. Within a short radius, more than ten waterfalls
tumble over the narrow, rocky courses of Silver Creek and its tributaries. This
number is possibly doubled during winter and spring, when runoff creates many
smaller waterfalls.
The
tributaries of North Silver Creek come from springs on the west slope of
Wildcat Ridge between Silver Falls State Park and the Opal Creek Wilderness,
while the tributaries of the South Silver Creek come from springs on the north
side of Fern Ridge. From where the two streams combine to form Silver Creek,
the stream continues northwest through Silverton and into the Pudding River. The
streams in the Cascades have the best water quality in the state. In addition
to the Cascade streams being the best in the state, the basalt acts as a
filtering mechanism that keeps debris out while the stream is underground.
Since there is no farming at the headwaters, pesticides and other chemicals are
kept out of the water within Silver Falls State Park.
After the Columbia River Basalt came through and
solidified, streams would form on top of the flows. While it is hard to
recreate what the first waterfalls would look like, there are a few possible
scenarios. One such scenario is that at one time, there could have been a
single, 500 foot tall waterfall that cascaded over every one of the basalt
flows. Another scenario involves a step like that of Multnomah Falls on the
Oregon side of the Columbia River Gorge. A third possibility is that there were
a series of steps, like a staircase. In each scenario, as a waterfall hit a
more resistant lava flow, it eroded more of the bottom layer, causing each
waterfall to erode at different rates. The flow rate of each creek also helps
determine the rate of erosion; a faster flow, like that of North Falls will
erode more than a slower flow, like that at Winter Falls. After the 1,500’ thick
blanket of the Fern Ridge Tuff was deposited, the waterfall, or waterfalls, may
have been as high as Niagara Falls for a short time until the tuff was eroded
away back down to the basalt.
Millions of years ago, the waterfalls in Silver Falls
State Park may have looked like a miniature version of Gullfoss (above) in
Iceland.
As
the waterfalls eroded away at the bases, the hard basalt on top breaks off
after a period of time and falls into the streambed below, this is termed
headward erosion. This erosion style also occurs at places such as Grand Canyon
National Park, where the uplift of the land has caused the Colorado River to
cut into the Colorado Plateau. Nowhere in the park is this erosion style more
apparent than in the streambed below North Falls, where bedroom-sized boulders
are waiting to be taken downstream one sand-grain at a time.
Over
time, a layer of soil began to grow whenever the walls of the canyon were
eroded to a slope suitable for accumulation of sediments and organic material.
Water percolated through the basalt, and where the casts of trees were
encountered, minerals were deposited.
Several car-sized boulders litter the base of North
Falls
During the Ice Ages, which were between 15,500 and
13,000 years ago, the floodwaters from Glacial Lake Missoula backed up in the Willamette
Valley, but due to the uplift of the silver falls area, the meltwater did not
reach the height of the park. At only 400 feet above sea level, the lake that
was created in the Willamette Valley was about 400 feet too short to even reach
the bottom of the stream in the northwest corner of the park. However, the
Silver Falls region did not completely escape the effects of the Ice Ages; in
certain waterfalls, notches have been cut out of the bedrock on the top of the
cliff where the water now pours through. These notches can be seen at North
Falls and Twin Falls as large gouge marks
As
the waterfalls and ice eroded the soft layers of sand that makes up the Vantage
Interbed, the tree casts were exposed, and in the case of South Falls, these
casts were eroded away into gaping holes. These holes are known as erosional
chimneys. The dark red soils of the nearby Salem Hills where the Willamette
Valley Vineyards are located would be what the soil in Silver Falls State Park
would look like if the grass was taken out.
The following
table includes the heights of 14 of the 15 falls, Frenchie Falls is not
included:
Heights of waterfalls in Silver Falls State Park
Creek Name Name
of falls Height (ft)
North Fork Upper North 65 feet
Silver Creek North 136 feet
Twin 31 feet
Middle
North 106 feet
Drake 27 feet
Lower North 30 feet
Winter Creek Winter 134
feet
Hullt Creek Double
178 feet
South Fork Lower South 93 feet
Silver Creek South 177 feet
Heights of waterfalls downstream of Silver Falls State
Park
Creek Name Name
of falls Height (ft)
Silver Creek Crag 12 feet
Elbow 20 feet
Canyon 10
feet
Lisp 5 feet
Sunlight 5 feet
The fourth part of the series is here: http://beavercountryramblings.blogspot.com/2012/12/the-story-of-silver-falls-state-park_6400.html
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