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Nancyann
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PostFri Dec 29, 2017 12:06 am 
Brushbuffalo, could you explain what geologic events would cause this giant chasm on Vesper Peak?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
And similar ones on Big Four?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17

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texasbb
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PostFri Dec 29, 2017 8:41 am 
Nancyann wrote:
Brushbuffalo, could you explain what geologic events would cause this giant chasm on Vesper Peak?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
That's obviously evidence of an alien ship crash landing many years ago. Sometimes they hit wrong and dig trenches. Sometimes they just scrape and burn the surface:
Don't overlook the obvious. smile.gif (Actually, I too am interested in knowing what did that to Vesper.)

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Mike Collins
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PostSat Dec 30, 2017 7:54 am 
Nancyann wrote:
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
The Swauk Formation rock intrudes into a section of the Index batholith here and I am wondering if this line is the border of that intrusion. It looks like a fault line and the North-South directed Straight Creek fault line is in this area too. But I too await Obi Wan Brushbuffalo's input.

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Brushbuffalo
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PostWed Jan 03, 2018 9:05 pm 
Doppelganger wrote:
my first inclination was towards natrolite or gypsum when I saw the radiating sprays and chalky coloration
Doppelganger, I wondered about the radiating crystal habit too., unusual for quartz. I am unfamiliar with natrolite but this mineral seems to be an example of it. Thanks for the knowledge.

Passing rocks and trees like they were standing still
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PostWed Jan 03, 2018 9:15 pm 
RichP wrote:
This is kind of big, but I'm curious about this formation on Mt Wow on the southwest side of MRNP.
Rock on Mt Wow.
Rock on Mt Wow.
Rich, when seeing layered rocks from a distance you can initially suspect you are observing either sedimentary or volcanic rocks. Mt. Wow is made of volcanic rocks, much older than Mt. Rainier itself. In your picture we see many layers. Consulting the Geology of Mount Rainier National Park ( USGS Professional Paper 444), the layers are part of the Ohanapecosh Formation, a thick complex of basaltic andesite flows and coarse mudflows. It is mapped as Tol, is Eocene in age, and in total is at least 7,000 feet thick. The prominent reddish zone is probably a zone of highly oxidized iron-rich fragmental strata. Note the grayish band within the reddish layers. It is probably a lava flow ( long since cooled, obviously lol.gif ).. In general in this picture, the wall-like darker gray strata ( lava flows) are more resistant than the light gray and tan layers of mudflow debris.

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Brushbuffalo
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PostWed Jan 03, 2018 9:44 pm 
Nancyann wrote:
Brushbuffalo, could you explain what geologic events would cause this giant chasm on Vesper Peak?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
And similar ones on Big Four?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
Nancyann, when you see an arrow-straight feature of size, it is almost always either a fault, a joint (fracture), or a man-made feature. There is a significant fault (Darrington- Devils Mountain fault zone) extending near the summit of Vesper Peak and there are contacts between three rock formations of contrasting resistance to erosion: granitic rock ( tonalite), metavolcanic rock, and sandstone. Faults and large joints extending up/down slope often channel surface runoff, and the prominent gash is most likely formed by that process....water running along a zone of weakness (fault, joint, or contact), thus deepening it. Edit: find Vesper Peak on Google Earth and zoom in. That gash is very prominent in the image and in it flows the exceptionally straight Stony Creek. Big Four is composed mainly of metavolcanic rocks. The very steep but not particularly deep valleys on the south aspect of Big Four are due to stream flow but not along any particular zone of weakness. Note how they are rather evenly spaced with ridges intervening. You can confidently distinguish between stream-eroded valleys (V-shape cross sectional profile) from glacial valleys (U-shaped).

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Nancyann
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PostWed Jan 03, 2018 9:51 pm 
Thanks for taking the time to answer my question, Brushbuffalo, and Happy New Year!

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RichP
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PostThu Jan 04, 2018 8:11 am 
Thanks Brushbuffalo. That's fascinating.

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gb
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PostThu Jan 04, 2018 8:26 am 
Brushbuffalo wrote:
Nancyann wrote:
Brushbuffalo, could you explain what geologic events would cause this giant chasm on Vesper Peak?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
And similar ones on Big Four?
Blue Mountain views 12/23/17
Blue Mountain views 12/23/17
Nancyann, when you see an arrow-straight feature of size, it is almost always either a fault, a joint (fracture), or a man-made feature. There is a significant fault (Darrington- Devils Mountain fault zone) extending near the summit of Vesper Peak and there are contacts between three rock formations of contrasting resistance to erosion: granitic rock ( tonalite), metavolcanic rock, and sandstone. Faults and large joints extending up/down slope often channel surface runoff, and the prominent gash is most likely formed by that process....water running along a zone of weakness (fault, joint, or contact), thus deepening it. Big Four is composed mainly of metavolcanic rocks. The very steep but not particularly deep valleys on the south aspect of Big Four are due to stream flow but not along any particular zone of weakness. Note how they are rather evenly spaced with ridges intervening. You can confidently distinguish between stream-eroded valleys (V-shape cross sectional profile) from glacial valleys (U-shaped).
For those who don't know Vesper, this south aspect is readily visible from many areas around the Seattle area. And the north side offers some of the finest granite rock for climbing in the state. I am enjoying these interesting conversations as well. Brushbuffalo, could you discuss a little about the geology of adjacent Sperry Peak? The climbing rock on parts of Sperry is very hard and has almost a quartzite like nature, with embedded round pebbles.

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Brushbuffalo
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PostThu Jan 04, 2018 9:55 am 
gb wrote:
Brushbuffalo, could you discuss a little about the geology of adjacent Sperry Peak? The climbing rock on parts of Sperry is very hard and has almost a quartzite like nature, with embedded round pebbles.
Sure, gb. Thanks for the question. Although I have been up Vesper I haven't ventured over to Sperry yet. So let's turn to the authority! Geologic Map of the Sauk River 30- by 60- Minute Quadrangle, Washington, by Tabor et al , Sperry Peak, just northeast of Vesper, is composed of sedimentary rock, mapped as formation Tbs. Most of this formation is sandstone but Tbs also contains conglomerate. Come to think of it, I remember seeing conglomerate boulders poking above snowpack on the trail to Vesper that must have been shed from Sperry. Here is a detail to look for on your next Sperry trip. Quoting from the map's explanatory notes: "Within the Darrington-Devils Mountain Fault Zone, conglomerate clasts are highly stretched, roughly horizontal, and parallel to the faults, suggesting strike-slip movement along the fault zone." cool.gif [An active modern-day strike-slip fault ( horizontal movement along the fault trace) is the famous San Andreas Fault Zone in California.]

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NorthBen
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PostWed Jan 10, 2018 1:20 pm 
Here's one that caught my eye this past summer, taken near the summit of Gardner Mountain:
Thoughts?

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Brushbuffalo
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PostWed Jan 10, 2018 2:50 pm 
NorthBen, thanks for the picture of that very interesting boulder. I have some comments based on location of Gardner Mountain and using the Geologic Map of the North Cascade Range by Ralph Haugerud and Rowland Tabor. To give you a more definite answer I would return to that fun choss pile again and carefully observe the bedrock outcrops over a wide area. I camped on top of Gardner many years ago, but was more interested in the goats and the rare "green flash" I saw at sunset so didn't pay enough attention to the rock. Part of the boulder is a course-grained conglomerate fragment consisting of subangular to subrounded clasts, including at least one granitic clast. The boulder is likely a bit of the bedding contact between a conglomerate and a very well-sorted sandstone. There are other thoughts I have about this rock that involve sketches, arm-waving, and other things not possible in this reply to your question. Fascinating, but I really need to be there to look around! Sometimes it's hard to identify a single "tree" outside of the context of the " forest." There are several different formations that occur on and around Gardner Mountain, which together are known as "rocks in the Methow block." You may have an example of the formation abbreviated Kpv, and this is part of the Pasayten Group, which also has a companion formation Kps ( sedimentary) found along the lower western base of Gardner over toward Abernathy Peak. Kpv is "predominantly andesitic breccia and tuff; locally fluviatile [river] maroon siltstone, sandstone, and conglomerate. About 90 million years ago, volcanoes erupted on the floodplains of rivers that flowed over sediments of the former Methow Ocean, burying both the river deposits ( Kps) and the underlying Methow Ocean sediments under volcanic rocks." However, the individual particles (clasts) in your boulder don't look to be volcanic. The maroon color, which is much more distinctive in some locations in the Methow region, is due to oxidation of stream-deposited sediment. There is another formation outcropping near the top of Gardner, Ktf. I recall seeing spectacular conglomerate boulders of Ktf on the PCT on the east slope of Powder Mountain between Rock Pass and Woody Pass, but I digress. Ktf is the Three Fools sequence, which is " predominantly thick-bedded sandstone, minor thin-bedded sandstone, argillite, and conglomerate deposited in deep-water submarine fans. Between 105 and 110 million years ago, ......volcanic islands formed in the western part of the Methow Ocean. The weight of these islands caused the ocean to deepen [isostatic adjustment]. Occasional flows of sediment-rich water ( turbidity currents), perhaps created by submarine landslides or storm waves, cascaded from the east and west into the depths to create these turbidite deposits." Problem with this is that the boulder is quite different than a turbidite. Please pardon my vagueness in this response. "it could be this, or that, or something else".....bottom line is I'm not very confident in a definitive ID as far as which formation this boulder was broken off from.. . dizzy.gif I often am challenged trying to identify a loose rock from a single picture without... or even with....scale, and without seeing it in field relationships. But I enjoy the challenge. It's fun to be conjectural, and probably makes for amusing (and maybe even occasionally informative) reading. winksmile.gif The North Cascades have some of the most complex geology anywhere. It has taken field geologists many decades to try to figure it out.....and they are still trying!

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Brushbuffalo
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PostSat Feb 24, 2018 11:05 pm 
Friends, This thread is called "Name That Rock" [changed to "What's this rock? What's that landform?"] and has attracted a moderate amount of attention. In reading miscellaneous trip reports, I frequently see pictures of grand landscapes with fascinating landforms and also images of rocks and minerals. Sometimes the OP will include a question about what they are seeing. I feel uncomfortable about just barging in with an opinion without being asked. To me, that is rude. To those to whom I have done that in the past, please accept my apology. Right now is slack season for many who otherwise might be traipsing about on exposed rocks and landforms. if you have questions about geologic things you have seen in your past travels, add a post to this thread and ask a question. If you see something geologic in another's post, ask me also, but out of courtesy please sent that person a pm asking for their permission to have me look at the image they posted. Please be aware of hints to allow me to make a reasonable explanation ( see the initial post): location, as precise as possible, and scale (size) if possible. Although I have been fortunate to travel, I do better with PNW stuff because I am more familiar with this region, plus I have geologic maps that help. Fossil images mess with my head unless they are common and obvious ( I'm not a paleontologist).🤔 No promises for positive identification, but it is fun to offer even a "best educated guess". With close to half a century of college geology teaching as well as extensive field work, I have seen a lot of rocks, structures, and landforms. We can all learn together! Doug

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texasbb
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PostSun Feb 25, 2018 1:14 pm 
Brushbuffalo wrote:
I feel uncomfortable about just barging in with an opinion without being asked. It is rude. To those to whom I have done that in the past, please accept my apology.
I, for one, would welcome unsolicited commentary on geology appearing in my pictures! If I've posted a trip report here, I assume it's an invitation for others to comment on it. No rudeness at all. But solicited opinions are great too! Here's one for which my assumption was adamantly refuted by a geologist friend. Her explanation makes no sense to me, so I'll ask for a second opinion. (I won't mention either my assumption or her opinion so as not to taint the well.) What geological process caused the paper-smooth side of this rock? This is right on the PCT in the Goat Rocks, and is about the size of a chest freezer, give or take. Many of us here have probably seen it.

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PostSun Feb 25, 2018 1:38 pm 
No idea what type of rock but guess it was at the bottom of a glacier.... (waiting to see if my guess is correct)

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