Forum Index > Trail Talk > Tunk Topography:  Fissures, Rifts or What?
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Sculpin
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PostFri Dec 11, 2020 1:05 pm 
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It's the winter of the pandemic.  We all need content.

I have long been fascinated by the area east of the town of Riverside, along the Okanogan River.  I will refer to this area as the Tunk after Tunk Creek, the stream valley just to the north.

As you drive north along the Okanogan on 97 south of Riverside, you can see some interesting looking canyons slanting down from the northeast on the far side of the river.  Then the highway swings away from the river.

Well, it turns out there is public land up in there.  So I puzzled over maps and determined that public access is quite limited, but there is a turnout and parking lot for hunters along Tunk Creek.  One fine spring day, some friends and I hiked up in there and found our way to a ridgetop in very scenic country.  Beyond the ridge, we got bogged down on steep talus in a weird fissure that seemed to go right across the top of the ridge.  We did not make it much farther, and retraced our steps. Intrigued, I have always wanted to go back but it keeps slipping.

As I have studied the area more, I became even more intrigued.  What the heck are these north-south trending fissures?  I cannot imagine them forming from water erosion or glacial action, although there is plenty of evidence of those forces in surrounding features.

If you open this link, activate Google Earth, and toggle back and forth between 2D and 3D, you can get an idea.

https://www.google.com/maps/place/Tunk+Mountain/@48.5235448,-119.4677686,8015m/data=!3m1!1e3!4m5!3m4!1s0x549d20333db8819b:0x75af51dd9dd343aa!8m2!3d48.5457121!4d-119.2361543

The N-S trending features are often very narrow, with near vertical walls.  They sometimes run right over a ridgetop, like a knife slice across a loaf of bread dough.  In places they are completed choked with brush or talus, impassible to humans.

If you look around a bit, the same features can be seen to the north, all the way past Tonasket, and also a little way to the south.  In other places the features are not as distinct, the fissures not as deep, but they look the same.

I actually went to the effort of trying to find out more information about Tunk topograhy through geological resources.  I even tried to see if I could find a graduate thesis at UW.  I have found nothing.

Does anyone know how these fissures formed?  My best amateur guess is that they look like they formed very rapidly under extensional stresses, but that does not seem to fit with what I have read about the formation and current status of the Okanogan Highlands.

I have another visit on my agenda for next spring...again.  rolleyes.gif

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treeswarper
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PostSat Dec 12, 2020 7:41 am 
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The geology class was always filled up by the time I had registered for required classes. 

I assumed erosion was the cause, but from the air, it does look different. I think the Missoula flood came through the area as did glaciers.  Is there a geologist in the house?  There is probably a book about the area.   The book store in Winthrop has books about local topics.  The museum in Okanogan might also have info, if they are open.  The same goes for the Tourist Info office located at the Omak Stampede Park.

A friend and I have a bike ride we love to ride in the Spring and Fall.  It is too snowy in the winter and too hot in the summer.  Rocks (erratics?) are found here and there.  I have a favorite rock on this route, and it is not the rock that can be peed behind.


I won't give the location.  Part of the enjoyment of the ride is that there is no traffic and a dog can go along and run.   Three vehicles is heavy traffic, although this has changed due to cleanup and reconstruction after the Cold Springs Fire roared through. 

The rock survived. 

Just please respect private property.  The people in the outlying areas have been traumatized by fires and don't need to worry about trespassers.  Our ride goes through private and Colville tribal land and we stay on the road and enjoy the sights from a distance.  The tribe is also sensitive about Covid.

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treeswarper
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PostSat Dec 12, 2020 8:05 am 
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Taken off McLaughlin Canyon road in early spring.  I turned around before making it up the canyon very far because of snow still packed on the road.  This is just south of Tonasket.

Looking at downtown Riverside.

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Mike Collins
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PostSat Dec 12, 2020 9:17 am 
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Maybe you can find some answers in either of this articles. The second especially in what the author identifies as Locality B.
https://www.sethckruckenberg.com/wp-content/uploads/2018/02/2011_Kruckenberg_Whitney_JMG-Spr-Oam_Gneiss_Okanogan_dome.pdf

https://www.dnr.wa.gov/Publications/ger_washington_geology_1988_v16_no1.pdf
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zephyr
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PostSat Dec 12, 2020 11:53 am 
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treeswarper wrote:
The book store in Winthrop has books about local topics.  The museum in Okanogan might also have info, if they are open.  The same goes for the Tourist Info office located at the Omak Stampede Park.

Yes, those sound like great resources.  But what about your local library?  Are you able to scan their collection using the search feature in their online catalog?  (I hope they are online.)  I often scan through the Seattle Public Library using "subject" and uncover books that way.  Also your library may have a relationship with other libraries in the area including university libraries.  That would widen your scope of materials. 

Sometimes if you can use Amazon for these subject searches to get some titles and authors.  And often they have descriptions or photos of sample pages that give you an idea of how good or useful the book might be.  And you can do a search on Abe Books and find decent used copies that you  can get for very reasonable prices  and add them to your collection if you have a favorite subject area.    ~z
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treeswarper
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PostSat Dec 12, 2020 12:30 pm 
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Believe it or not, I have been quite disappointed in the online library system here.  The Timberland library seemed much more user friendly and had more resources--at least what I could find.  I've not been inside the local library for almost a year.  It was closed for most of the year anyway.

What is really odd is that the tiny Randle library puts on so many kid friendly activities (when no pandemic is going).  They've had once a week teen nights where they have free pizza for kids.  There is nothing like that here, in a bigger community.  I think a lot of it has to do with who the head librarian is.

But I can go for a bike ride where few cars are encountered. 

I still need to go see  The Balanced Rock, which is near Omak Lake.

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PostTue Dec 15, 2020 8:48 am 
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Mike Collins wrote:
The second especially in what the author identifies as Locality B

Thanks Mike!  That is another one that I had not previously found.

At locality B the author is certainly standing in the right spot looking at the right features. Unfortunately he does not talk about the most pronounced visible features, the deep N-S cuts in the landscape.  However, later in the same paper, he refers a few times to "meltwater cuts."

Too bad the glacial features articles are paywalled, ain't doing that.

The thing that struck me about these "cuts" is how raw they are, full of unweathered boulders of various sizes.  It did occur to me that the scabland coulees of Washington state are in places just as raw, but I also know that the Bretz floods did not go down the Okanogan.

One plausible explanation is that the main channel of the Okanogan was blocked by ice at Riverside at some point, and the meltwater was forced over the top and down these channels.  That is, after all, how Wagonwheel Coulee, the route Highway 97 follows, originally formed.  It must have been a crazy amount of water to cut these channels so deep in such a short time!  The problem with that explanation is that the same set of N-S cuts appear to the north and south.  Perhaps all the drainages off of what would have been the ice-covered Okanogan dome were blocked at the bottom by ice, resulting in south-trending "meltwater cuts" in numerous locations.

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PostTue Dec 15, 2020 11:06 am 
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A good portion of the Okanogan Valley is a fault.  I think I first read this in a Canadian article and then looked it up on a map.

The Missoula Flood was more to the south.  I expect my rocks were moved by glaciers.

As to all the little gullies, I just assumed they were caused over many years by erosion.

Was once told by a new ager off the grid person that Mt. Hull had areas of good vibrations.  I never found any good or bad vibrations in that area.  There was also a tree named Fred somewhere on Mt. Hull.  Fred probably burned up since those times.  Mt. Hull is closer to Oroville.

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PostTue Dec 15, 2020 12:08 pm 
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treeswarper wrote:
As to all the little gullies, I just assumed they were caused over many years by erosion.

Perhaps meltwater erosion, but whatever it was occurred quickly.  You should check it out since you live really close.  From the public parking spot on the south side of Tunk Creek, you can see an old abandoned road snaking up to the southwest.  Just head for that road (it is a little upsy downsy on the way in and out of shallow gullies) and follow it up.  When it peters out just keep going up until you hit an E-W trending road, turn right (westerly) and explore.  It is all open open woods or steppe and easy walking  and would be great for your dog!  Somewhere in there are some of the last remaining leks of the sage grouse although they won't be around this time of year.

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Anne Elk
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PostTue Dec 15, 2020 2:16 pm 
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That area looks to be at least on the periphery of the Ancient Lake Missoula floods that also created the channeled scablands.  You might check out the offerings by Nick Zentner, geology prof at CWU to see if any of his lectures include that area.  Or send him an email. Nick has a number of fans on NWH; his lectures are as entertaining as they are informative.

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PostWed Dec 16, 2020 8:34 am 
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Anne Elk wrote:
That area looks to be at least on the periphery of the Ancient Lake Missoula floods that also created the channeled scablands.

It's not far away, and the cuts may well be coulees.  But they are not part of the channeled scablands created by the Missoula (nee Bretz) floods.  Those waters came from the Clark Fork River and washed across the plateau. The northern extent of the floods is bounded by the Spokane River to the east, and the Columbia farther west.  Even Moses Coulee is not really part of the scablands, it was carved by the full flow of the glacial Columbia during peak glaciation when the  main river channel was blocked by continental glacier.

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Anne Elk
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PostWed Dec 16, 2020 8:43 am 
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Sculpin wrote:
they are not part of the channeled scablands created by the Missoula (nee Bretz) floods.  Those waters came from the Clark Fork River and washed across the plateau.

I need to refamiliarize myself with that phenomenon - so fascinating.

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PostFri Dec 18, 2020 7:56 am 
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Anne Elk wrote:
I need to refamiliarize myself with that phenomenon

Last minute gift idea:

"Cataclysms on the Columbia" by John Eliot Allen and Marjorie Burns.  The second part of the book is very handy for field trips in the spectacular scablands.

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PostFri Dec 18, 2020 9:08 am 
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I am no geologist, but I have watched about 100 hours of Nick Zentner this year.  lol.gif

I don't think these fissures have anything to do with flooding or glacial erosion. To me it looks more like a chunk of bedrock that has risen and expanded. The expansion causes faults breaking up the bedrock into blocks. Some of the blocks sink creating the N to S fissures, which are then further widened by weathering. Kind of like a basin and range topography on a much smaller scale.

I have no idea if this is true, just a hypothesis.

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PostFri Dec 18, 2020 10:27 am 
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nickmtn wrote:
I am no geologist, but I have watched about 100 hours of Nick Zentner this year.  lol.gif

I don't think these fissures have anything to do with flooding or glacial erosion. To me it looks more like a chunk of bedrock that has risen and expanded. The expansion causes faults breaking up the bedrock into blocks. Some of the blocks sink creating the N to S fissures, which are then further widened by weathering. Kind of like a basin and range topography on a much smaller scale.

I have no idea if this is true, just a hypothesis.


Sounds good.  If you look at aerial photos along the Okanogan Valley, there is more of this to be seen than just around Riverside. 

The valley is partly on an earthquake fault.   Don't know how major of a fault though.  It isn't shown on many of the maps that appear when googled.  It is overshadowed by the westside faults which are more famous.  I think the Canadians have better info on it and definitely have a larger population in their Okanagan Valley.

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