Tuesday, May 23, 2017

High Water Across the West: The Humboldt River in Carlin Canyon — With the Carlin Canyon Unconformity!

Well, there we have it: the Carlin Canyon unconformity with the Humboldt River running nearly bankfull on April 11th of this year.
Looking downstream, back toward the tunnels, we're actually still looking at the unconformity, but it's cropping out poorly on the slope below the tilted limestone beds of the Pennsylvanian-Permian Strathearn Formation.
I went ahead and cropped the best photo I took so we could zoom in on the unconformity in it's classic exposure, and then drew a line right along the contact.
The Strathearn lies unconformably over the near-vertical (to locally overturned) Mississippian-Pennsylvanian Diamond Peak Formation, which is sometimes mapped as the equivalent Tonka Formation in this area.

Zoom in on this feature with a GigaPan by Ron Schott. And if you click the Google Earth link below his GigaPan, you can view the feature *and* the GigaPan in Google Earth!

Tuesday, May 16, 2017

High Water Across the West: Honey Lake

I've recently had the opportunity to travel across part of the Great Basin of eastern California and northern and central Nevada, and have noticed a lot of high water, almost everywhere. Honey Lake, which has been dry to only partly filled during the last several years, is once again a lake. The first two photos are from the 11th of April; the last three are from the 25th.
The lake is beyond full for what has been typical for several years, with bushes drowned around the edges and fences under water. In fact, you can see a bit of a fence or gate in the picture above, near shore, a little right of center. Most of the fenceline is completely under water.
Here's a relatively broad view of the lake taken on April 25th.
I cropped the previous photo so it would closely match the first photo from the 11th.
And this photo matches the second photo from the 11th. If you look closely at the two matching sets, you can see that the water was slightly higher on the 11th, and had gone down a teensy bit by the 25th.

I have several years of pictures of Honey Lake: there are these comparison photos from 2007 through 2011, these few photos from May and June of 2015, and one photo from early March, 2016. Even more photos can be found by searching the blog for "honey" (along with a few from nearby Pyramid Lake). Most of my photos through the years have been taken from the Honey Lake Rest Area).

Thursday, May 11, 2017

A Micro-Bloom

I pulled off for a pit stop at Bob Scott Summit and started seeing little tiny wildflowers everywhere. I looked around, hoping to see a superbloom, like so many were reporting this year, but the flowers were either somewhat far between, or—where covering the ground—were itsy bitsy.
Spring was just beginning on the second highest summit along Highway 50 in the Toiyabe Range of central Nevada, so I suspect that these flowers are just the start of what might be spectacular in places later this month, or even in June or early July.
I don't have the names of all these flowers, but the first photo features locoweed (Astragulus sp), and the second photo is of Phlox (Phlox sp.).
Here, a few sunflower-family plants are starting to come up; these are either Wyethia or Balsamorhiza of some type (likely the former, I think). I don't know what the little blue flowers are, but they are beautiful.
And here is some locoweed again, with a few white flowers, possibly Eriogonum, and more unknown tiny yellow flowers.
Barbecue down!
In a few of these shots, I got really low to the ground to try to make it look like some of the more spectacular superbloom-type photos, wherein you can see flowers up close going off into the distance...
...but that didn't really work for me, and getting a good focus was problematic.
Nevertheless, I persisted, and got some good photos of several different types of wildflowers.
Too bad I won't be passing this way until sometime in July. Perhaps the lupine, which has been forming thick fields up on top of Austin Summit ever since a burn in the 1980s, will be blooming then, but the flowers at this lower pass will most likely be done.

Tuesday, May 9, 2017

Pine Valley and Carlin Canyon Squiggles

What is this?!!1?1!?
It all started when I was trying to find out what rock formations and rock types I was seeing while making the long trip to work and back out near Elko. Looking around, I found this geologic map (Smith and Ketner, 1972), which even had a kmz file so I could load it directly into Google Earth—and so I did.

There I was, fiddling around looking at rock types and contacts. The map wasn't easy to look at in Google Earth (GE) because it was in black and white, so I started drawing the contacts on to GE, and lo and behold, the contacts were all screwy. It took me a while to figure out that the kmz file didn't register properly on GE; perhaps it didn't have a NAD27 to WGS84 correction or some such thing. I plotted a few static, known localities that I could identify on both the map and GE and determined that everything was off in a northwesterly direction (map to GE) by about 1500 to 1900 feet.
The map and GE locations of a small dam and the ghost town of Palisade.
I thought Palisade looked occupied the last time MOH and I visited, which was in the summer of 2013 (it was the only time either one of us has ever been there), so I was surprised to find it listed by search engines as a ghost town, rather than as a "census-designated area."

I was frustrated by this mis-registration of the map on Google Earth—what is the point of a kmz file of a map, after all, other than to be able to use it easily and forthwith—so I continued drawing on a few contacts in the area I was initially interested in: the area near the small (or old) dam shown above.

Oh look, there's a huge landslide or slump block mapped! I always find these fascinating, so I zoomed in on that, after figuring out that, indeed, I had stopped along the road once—in a pullout near the dam—and had found ash-flow tuff in the roadcut, just like I had remembered! (Although in this case, it was probably slumped or slid ash-flow tuff rather than 100%-in-place ash-flow tuff.)

And then I remembered that I'd always thought there was a pediment in Pine Valley, and recent drives through the area seemed to confirm that, though I wasn't sure if it would be considered a pediment because it seemed to be formed on Quaternary-Tertiary sediments. A couple of old reports (Regnier, 1960 and Eakin, 1961) confirmed that a pediment (or two, even!) had been identified in the valley—and that's when I went nuts with my GE squiggles, and started drawing in all the Quaternary gravels so I could better visualize the valley's geomorphology. That resulted in the squiggles seen in the first image: an incompletely labeled map with missing contacts but with pediment gravels outlined in great detail.

Then, I moved up to Carlin Canyon and—unsuccessfully in my opinion—tried to plot the unconformity contact. (See Ron Schott's Gigapan of the Carlin Canyon unconformity here.) And then I moved to the Carlin Formation east of the Carlin Tunnels. The Carlin Formation forms golden-brown outcrops and cliffs right alongside the highway, great examples of tafoni weathering, so close but inaccessible. I wanted to see if any roads led into the area, and there are none, but I drew some squiggles for the geology in that area anyway, and then moved south of the highway to draw in a few more areas of the Carlin Formation, because once I've started on something, it's hard to get me to stop.
An expanded version of my GE squiggles.
And that's what it all looks like at this point. Hopefully I'll be able to grab a few great photos of the pediment surfaces later this summer, when I move back into the area for another round of work way out there.

By the way, the completed geologic map (Smith and Ketner, 1978), published in color, can be viewed here (but without a kmz file).

Tuesday, April 25, 2017

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.