Thursday, March 10, 2016

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 hanging wall 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 hanging wall 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 hanging wall of the main shear zone. The slightly steeper hanging-wall 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 hanging wall 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 hanging-wall fanglomerate.
This photo shows more older alluvium in the hanging wall 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.


BJ Nicholls said...

Looks like lesser mohavea – Mohavea breviflora. In the plantain family and closely related to snapdragons.

Silver Fox said...

Thanks! :-)