From the Road: Some Nice Gneiss

Every time I drive Highway 6 between Idaho Springs and Golden, Colorado—and I almost always take that route when heading east, rather than the section of I-70 between Idaho Springs and the hogbacks—I try to get a few photos of the great gneiss forming the canyon walls. If I'm going eastward, it can be hard to stop because I'm almost there. This time, in the fall of last year, I was heading west, but I still found it hard to stop, partly because of traffic and unexpected road work. Nevertheless, I managed to make a few pullouts that were rewarding.

The first shot is typical of the biotite gneiss that underlies much of the region: darker bands with more mafic minerals, and lighter bands composed almost entirely of felsic minerals.

Here's a little more of that same biotite gneiss showing complicated deformation.

The geology of the area, seen below in a cutout from a USGS map, looks a little complex! Our first two photos (the two easternmost dots that are rather close together) are in what is mapped here as Xb: Proterozoic biotite gneiss.

Map courtesy USGS (Kellogg et al, 2008).

A little farther into Clear Creek Canyon, I pulled over and grabbed a couple shots of this second roadcut (single dot to the west, above), primarily because of all the light-colored dikes and masses. These rocks are probably what is mapped as Xh: hornblende-plagioclase gneiss and amphibolite.

All of the rocks we're looking at today are thought to have originated as sedimentary and volcanic rocks that were deposited in a basin 1780 to sometime after 1750 Ma (million years ago), as per this pamphlet accompanying the map.

A shot of the entire roadcut. 

Somewhat darker gneiss is above somewhat lighter gneiss in this roadcut. The darker portions may qualify as amphibolite, which is part of the Xh unit.

The same gneiss, zoomed in a bit.

I noticed what looks like a little folding while I was processing these photos, so I drew in a few lines. The rocks look darker inside the fold nose, and there has been a lot of injection of the light-colored material, which might include felsic dikes like aplite or pegmatite, and also might include some quartz veins. I really don't know how common quartz veins are within these gneisses, and the roadcut is too close to the often busy, narrow and windy, two-laned U.S. Route 6 for safe examination.

If you want to see more of these rocks, here is Robin Rohrback's set of gigapans of the roadcuts along this stretch of Highway 6, along with gigapans of hand samples of the gneiss.

Reference:
Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R., 2008, Geologic map of the Denver West 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3000, scale 1:100,000, 48-p. pamphlet.

From the Road: Whipple Mountains

Savahia Peak in the Whipple Mountains, with cholla.

And here's a cartoon of the geology.

The upper plate volcanic rocks are dipping moderately to steeply to the west (cyan bedding). The Whipple Mountains detachment fault (hachured dark blue) is fairly flat-lying in this area, separating reddish, hematitic upper plate rocks from greenish, lower plate chloritic and mylonitic gneisses. I've drawn in a few approximately located listric normal faults in bright blue to illustrate the general structural configuration. The upper plate has moved to the east relative to the lower plate, as indicated by both the dip of beds in the upper plate, and (especially) by the movement on upper plate listric normal faults.

From the Road: Fall Color along the West Walker River, CA

We're looking southwest at mountainous terrain along the West Walker River, with what looks like granitic rock—the light-colored rocks in the foreground and on the tree-covered high slopes in the background—and some dark-colored, mafic-looking rocks exposed in the middle-distance ridge that slopes down toward the river from right to left. These mountains, which are on the west side of Highway 395, are technically part of the Sierra Nevada.

Death Valley Trip, Part 2: More of the Badwater Turtleback Fault

If you remember from a couple days ago, toward the end of the first of, hopefully, a few more posts about our trip to Death Valley and vicinity, we had walked up an alluvial fan down near Badwater and were looking at the Badwater Turtleback fault, which is essentially the entire range front above. Specifically, we were at the smooth, olive-brown surface on the far right edge of this first photo.

Not incidentally, these photos were all taken during the early days of this year's Death Valley "superbloom." We'll see some wildflowers in this post, but I'll be concentrating on the turtleback or detachment fault surface and not the flowers.

The Badwater Turtleback fault surface, looking north. Part, but not all, of the apparent curvature in this photo is from the 18mm wide-angle view (27mm in 35mm equivalent).

I was surprised to find what looked a lot like Quaternary or late Tertiary alluvium—alluvial fan, talus, or basin fill deposits—sitting in the upper plate of this fault, so I took quite a number of photos.

The apparent dip on the alluvial deposits is shallow, dipping slightly back to the east. This is only apparent dip, however.

I wondered if the older alluvium (older than the material on the active fans we had just hiked up) had been deposited right against the fault plane (the turtleback faults are often exposed, with hangingwall rocks having been stripped of by post-fault erosion), or if the deposits were, indeed, cut by the fault. If I could just get closer—close enough to touch the fault plane or the deposits—maybe it would be clear that this was a bunch of post-fault debris covering the fault. I couldn't, and it wasn't. The light brown, fairly poorly sorted material is definitely in the hangingwall of the fault: while there I could see visual evidence of shearing.

In this photo, you can see a more steeply dipping fault cutting the fan deposits in the hangingwall of the main shear zone. The slightly steeper hangingwall fault may flatten toward the main shears, but that's really unclear.

When checking out the literature after the trip, I found that, indeed, the hangingwall of the Badwater Turtleback fault or detachment does contain Pleistocene fanglomerate deposits (Miller and Pavlis, 2005).

Here we're looking up the plane of the fault surface, a kind of disorienting view.

The shadowy blob in the upper right (above) is part of the same shadowy surface seen in the next photo (below), and the light colored mass that looks like it's about to slide down on the photographer (me!) is another, larger mass of hangingwall fanglomerate.

This photo shows more older alluvium in the hangingwall of the turtleback fault surface, with the younger alluvium of a talus cone to the right. Notice the nice greenery with smallish flowers on the talus.

I scrambled upward near the base of the turtleback, but the terrain was a lot steeper than it looks in these photos, and the heat was getting to me some: although it was only 87° F (cool by Death Valley standards), it was a lot warmer than the 30s to 60s that I was accustomed to. Also, I had taken a scary tumble in Titus Canyon earlier that day, and wasn't comfortable with the steep slopes. I probably would have benefited from sturdier boots.

MOH looks up at the fault plane on the south side of the little drainage area or canyon near the base of the turtleback surface.

The same surface, perhaps a little closer.

Fault surface with wildflowers.

Because I couldn't get right up on the fault, I took these photos of a slickensided surface in float. Also, these tiny flowers—white with yellow centers like little daisies, tiny purple blooms, and others—were everywhere along the talus-ridden slopes.

The faint slickenlines are running across the photo here (same piece of float).

We walked back down the fan. It was easier going down, as it usually is, and I took a line more in tune with the recent rills and rocky, sandy washes, which no doubt ran last October when storms washed out numerous roads in the Death Valley area.

The turtleback fault plane is exposed in the shadows of a "slot" canyon just south from where we hiked up. Note the greenery with tiny wildflowers all across the fan.

And here's one of the tiny flowers. Does anyone know what this is?

(It's hard to Google "yellow wildflower death valley" right without coming up with just the desert gold.)

The Badwater Turtleback fault and a bit of desert gold.

We take one last look at the alluvial fan, the flowers, and the Badwater Turtleback. The flower show is dominated by yellow desert gold and purple notch-leaf phacelia.

Say goodbye to Badwater, before we head north.

    Location map:

Selected Reference:
Miller, M.G., and Pavlis, T.L, 2005, The Black Mountains turtlebacks: Rosetta stones of Death Valley Tectonics: Earth Science Reviews, v.73, p. 115-138.

All photos in this post taken on Leap Day, 29Feb2016.

Death Valley, "Super" Blooms, Turtlebacks, and Detachments

Looking southeast from the alluvial fan coming out of Titus Canyon.

When MOH and I came into Death Valley at Titus Canyon (and that's another story) on Leap Day, February 29th, we didn't see very many flowers right off, although it looked like Titus was poised to bloom heavily in a couple weeks or so (will we be back?). We had heard in Beatty that the best area was down near Badwater, so we headed that way, driving south on the paved Scotty's Castle Road (AKA North Highway or Bonnie Clare Road—Clare or Claire, whichever).

Approaching the junction of the Scotty's Castle Road with Highway 190, things started looking up. (By the way, Scotty's Castle Road was closed to the north while we were there, with no known opening date, as was a good portion of the Badwater Road, so be sure to check road conditions if you go!)

Looking southeast toward the Black Mountains, with the Badwater Turtleback coming into view beyond a carpet of gold.

The turtleback is the humped part of the mountain to the right of the varicolored volcanic and sedimentary rocks that sit in the hangingwall of the Badwater Turtleback fault near the Artist's Drive area.

Overall, things did get perceptibly better south of the junction with 190, where we turned on to the Badwater Road.

Our first view of the Death Valley playa, looking south toward Telescope Peak.

In the wash photo above, Telescope Peak is a faint bluish bump at the top of the Panamint Range in the distance on the right. A few footprints cut across the photo in the lower left, probably attesting to one of the many photographers and desert enthusiasts that were in the area during our short visit.

The vast majority of the color—a bright yellow gold—was from one plant, Geraea canescens, AKA desert sunflower, hairy desert sunflower, or desert gold. (I prefer the latter.)

I didn't take very many closeups of flowers, but I got a good one of the desert gold:

Desert gold, just north of Furnace Creek on March 1st.

Desert gold in a dry wash, with a bit of the Black Mountains in the background.

A view of low hills, looking south, from north of Furnace Creek.

We passed through Furnace Creek as quickly as possible, moving even farther south on the Badwater Road. Bicyclists cluttered the highway in places; I think a race or tour of some sort was in progress. We slowed constantly (unlike a few rude and dangerous drivers that I hereby excoriate) for photographers, road-crossers, bicyclists, and other miscellaneous travelers.

Turtlebacks and the salt flat came back into view.

The Badwater Turtleback and the Badwater Turtleback fault dominates this view of the Black Mountains range front.

A bit of the varicolored, Mio-Pliocene Artist Drive Formation is visible in the low hills to the far left, with reddish rocks to the right at least partly consisting of the late Tertiary Greenwater Volcanics in the upper plate of the turtleback fault. The greenish rocks forming the turtleback surface are mostly mylonites, gneisses and marble of the lower plate.

Turtleback and superbloom.

Desert gold (et al), the Death Valley salt flat, and the Panamint Range.

Looking south toward Badwater Basin, the lowest point in North America.

We drove past Badwater, where the parking lot was full, and turned around at a point just past the alluvial fan seen above.

We weren't seeing a lot of flowers at this point, although there was still quite a variety, so we turned around.

I grabbed a photo of this small alluvial fan. You can see some flowers if you look closely.

And I took this photo of a desert five-spot (Eremalche rotundifolia).

Driving north from Badwater, we decided that we had to stop and walk up to this fine exposure of the Badwater Turtleback fault, which is a detachment fault in my book, but may or may not be regional in scale, so may not technically qualify (Miller and Pavlis, 2005).

Detachment fault with superbloom flowers, one of at least two purple types.

Ah, it's only a little farther—and it's only 89 degrees! (That's the temperature in degrees Fahrenheit, not the dip on the fault. The dip was about 45 degrees.)

Fault plane with desert gold on the fan in front of it.

Turtleback fault with various flowers and greenery.

Yay! We're there! What's that in the hangingwall???

    Location map:

I've added a real location map here, because the "Location" feature offered by Blogger (below, where it says "Death Valley, CA, USA") is no longer as functional as it used to be. The default view for this map may change as I publish new blog posts, and I will add additional photos and possibly additional features as I go along. Right now the default view is centered over Death Valley. The purple pins are photo locations.

If anyone knows of a simple way to change Google's embed code to add a centered location and a height ("z" or "zoom") when embedding a MyMaps map, please let me know. I probably won't be able to use java or other fancy attributes here on this blog. The embed code looks like this:

[iframe height="500" src="https://www.google.com/maps/d/u/0/embed?mid=z5SoVdoeVNqI.kHrJd949dnkE" width="500"][/iframe]

Selected References:
Greene, R.C., and Fleck, R.J., 1997, Geology of the northern Black Mountains, Death Valley, California: U.S. Geological Survey Open-File Report 97-79, 110p.

Miller, M.G., and Pavlis, T.L, 2005, The Black Mountains turtlebacks: Rosetta stones of Death Valley Tectonics: Earth Science Reviews, v.73, p. 115-138.

Read more about the "superbloom" here (Geotripper), here (National Geographic), here (NPS), here (Death Valley NPS Facebook page), and here (U.S. News).

The Conclusion of Our Float Test

We're about to test the rocks I posted about last week.

We have six float candidates (description here).

I voted for rocks #2 and #3 (as counted from the left in the photo shown above), with a "might" for #1 and "probably not" for #5. I did have the distinct advantage of being able to hold the specimens, thereby testing the heft

In comments, I got votes for:
1) Howard: none of the above
2) Lockwood: #3, with maybe but "I'd guess not" for #1 and #2
3) Ivar the Old: #3 (after thinking about #2 and then throwing it out)
4) Mathias: #3 and #2 (a "maybe" on the latter)

Rock #1. The larger of our two scrubbing stone rejects.

I wasn't sure if this rock would float: It has a lightweight heft for it's size, but I'm more used to feeling the heft of hand sized rocks, testing to see if a rock is limestone/dolomite v. barite, or limestone/dolomite v. fine-grained diopside skarn. I placed it carefully into the water, with one flat side down rather than end on into the water.

It's floating!

It's bubbling like crazy, and so I suspect the smallish vesicles will fill up with water, and when it gets completely waterlogged, it will likely sink (not a part of this test).

Rock #2: The smaller of our scrubbing stone rejects (remember, you can read more about these scrubbing stone rejects and see more detailed pics here).

I voted that this rock would float, although truth be told, the vesicle size is very similar to that of Rock #1 (so why didn't I vote for both of them?).

It's floating!

Possibly a higher percentage of the upper surface, compared to the upper surface of Rock #1, is sticking up above the water, but it's hard to judge the relative percentage of the entire rock in comparison with #1. And once again, I think it would probably become waterlogged eventually, and then it would sink.

I was sure that Rock #3 would float. It's a large piece of classic pumice.

Yep, there it is, floating. Most of the rock is sticking out above the water, almost the reverse of the previous two examples.

The pumice has small to very large vesicles.

Close-up of the largest of the air pockets or vesicles.

Overall, the pumice is quite frothy looking.

Rock #4, a piece of banded rhyolite glass.

I knew this rock would sink but included it in the test because it's composed of glass of about the same chemical composition as the glass in the previous three rocks.

It's on the bottom, no surprise.

Rock #5, vesicular rhyolite, also from Glass Mountain.

This is a large rock, lightweight for it's size, but it felt denser to me than the scrubbing stone rejects (Rocks #1 and #2) and doesn't look as vesicular. Consequently, I expected it to sink.

I placed it into the water with one of the flat sides down, and let go of it slowly.

It's definitely on the bottom.

Rock #6, a flattish piece of slaty phyllite.

I knew this rock (which is not a single large piece of mica) would sink, but I included it in order to a test of a rock with a different makeup than the other five. I also chose it for it's flat shape, to test whether the shape might make it float.

Nope. It's gone.

Three of five rhyolite samples from Glass Mountain floated and could therefore be called pumice. Their vesicularity, in order from most vesicular to least vesicular, is as follows: Rock #3, Rock #2, Rock #1, followed by Rock #5, which didn't float, and followed a long ways by Rock #4, which also didn't float. The difference between Rock #5, an example of vesicular rhyolite flow rock, and Rocks #1 and #2, pumiceous rhyolite flow rocks (the scrubbing stone rejects) is not great and might not be apparent when doing field work. Rock #4, which consists of dense, glassy banded rhyolite, is not vesicular at all. Rock #6, not a volcanic rock and not from Glass Mountain, also didn't float. It probably has a density similar to or slightly lower than the density of the dense rhyolite glass of Rock #4.

And that concludes our float test.