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.

Tuesday, April 11, 2017

From the Road: The Book Cliffs in Western Colorado (Mount Garfield)

Earlier that day (the same day I stopped in Parachute and Rulison, resulting in three posts about the Roan Cliffs), I had pulled over at the convenient viewing pullout on I-70, which is east of Grand Junction and a bit west of Palisade. It's hard to pass by this cliff, part of the Book Cliffs, without taking a picture or two. This time, unlike most other times, I took only one photo!

The Book Cliffs are capped by sandstone and lesser shale of the Upper Cretaceous Mesaverde Group, which overlies shale and minor siltstone and sandstone of the Upper Cretaceous Mancos Shale. The Mesaverde Group (sometimes Formation, see Geolex) usually consists of several recognized sandstone tongues, members, and formations, with intertongues of Mancos Shale in its lower part. In the area of these photos, the mapped sandstone formation—the buff-colored cliff-former above the Mancos—is the Mount Garfield Formation, obviously named for Mount Garfield, the highest point above the cliffs, on the upper left.
I cropped the photo to zoom in, partly because the nearly white layer just below the sandstone cliff caught my eye. While here, we might as well take a peek at the geologic contacts.
Kmg is the Mount Garfield Formation; Km is the Mancos Shale. The contact I’ve drawn in is largely from the Geologic Map of the Clifton Quadrangle, Mesa County, Colorado (Carrara, 2001), with extrapolation from the Geologic Map of the Palisade Quadrangle, Mesa County, Colorado (Carrara, 2000). The contact very roughly approximates the one shown on the Macrostat online geologic map.

Other photos of mine of the Book Cliffs can be seen here (photos from 2006) and here (photos from 2008). Also check out Ron Schott's GigaPan of the cliffs.

Tuesday, April 4, 2017

From the Road: Talus-y Goodness and More of the Roan Cliffs, and a Question (at the end)

I was looking back through some photos and realized I had some of the Roan Cliffs from the spring of 2006. These first two photos are taken from an impromptu campsite MOH and I found not far from the Rulison exit on I-70, and they somewhat approximate the views seen in Ron Schott's excellent gigapan of the cliffs. I'd embed the gigapan here, but Blogger seems to have some problem with either the iframe coding or the flash implied within the code (or maybe it's Chrome, and I'm being deluded as to what's possible). In either case, we're looking northwest toward the cliffs in the first photo (above), and northeast toward the cliffs in the second photo (below).
It was a very green spring, according to these photos, so the color balance doesn't match with my fall 2016 photos below, which were taken from near or at the Rulison exit. Also, my Nikon tends towards blue.
The reason I stopped for these particular photos during my semi-mega roadtrip of last fall was the talus. I found the striping caused by alternating zones of vegetated and non-vegetated slope areas to be fascinating in the way that perhaps only a geologist, geomorphologist, or photographer can. So I grabbed a few quick shots focusing largely on the talus slopes. More recently, I decided some approximated geologic contacts were in order.
In this photo (above), the cliff and talus slope below the cliff are formed on the Tertiary Green River Formation (Tg), and the colorful beds near the bottom of the photo consist of the Tertiary Wasatch Formation (Tw). The thin cyan line near the base of the cliff marks (hopefully) the top of the Mahogany ledge as extrapolated from this USGS preliminary geologic map, as deduced from this report (Fig. 9, p. 16)—which points out the top of the ledge in a cliff to the west—and as mapped from Ron's gigapan of the cliffs. A few other reports were helpful for exploring the general geology and reading some background info about the ledge and zone—it's called the Mahogany zone when intercepted in drill holes.
In this set of two photos, I've zoomed in on the striped talus section that was on the far right of the previous two photos. The vertical striping of the talus contrasts nicely with the horizontal layering of the Wasatch beds, don't you think? I've labeled the photos below. This time, a tiny bit of the Tertiary Uinta Formation (Tu) is barely visible at the top right. The stratigraphic contact between the Tg and Tw is crudely outlined in faded cyan: It crops out behind the foreground slope where we can't see it.

This set of two photos is not that different from the previous set, but here (below) I've sketched in the Mahogany ledge (as approximately extrapolated), and I've broadly labeled the geologic formations without drawing in the contacts. The circle is where an old mine, the Rulison Oil Shale Mine is shown on the topo map of the area  (USGS TNM 2.0 Viewer link). I can't see it there in the photo—though maybe it's just not apparent—but there is a tiny black area that *might* be an adit just beneath the arrow.
The cliffs in these 2016 photos lie northwest of the Rulison exit and occur between the first two 2006 photos.
In this last set of two photos, we're looking northeast from the Rulison exit, zooming in on cliffs that approximate what we can see in the second of the two 2006 photos. I once again focused in on striped talus, but then I really zoomed in on some switchbacked roads that I thought might be drill roads. It turns out that the switchbacks climb up to some underground workings into the Mahogany ledge, which I've marked approximately with a thin cyan line (below, with thicker lines marking formational contacts; Tu = Uinta Formation; Tg = Green River Formation). The line is taken directly from the previously linked-to preliminary geologic map of the Anvil Points Quadrangle (O'Sullivan, 1986). The map can be viewed directly in Google Earth, an option I always appreciate.

The underground workings here consist of several adits comprising the Anvil Points Oil Shale Mines. The mine was active intermittently from 1925 to 1982 (the last link includes some undated photos), with some clean-up operations running from 2008 to 2013.
How do you spell Talus-y? I see 3 options: talus-y, talusey, and talusy. I went with the first option in the title but prefer the last. Yes, I know it's not a *real* word.

Tuesday, March 28, 2017

Tales of the Mojave: A Dry Placer

And now, let us continue with my Tales of the Mojave series. In our last post, we had barely left town—town being Reno, NV, hundreds of miles to the north, and we being Allie and I, two young and fairly junior geologists: I was beginning my fourth full year as an exploration geologist; Allie was beginning her first. Besides the several recon targets I had generated while we were still in Reno, we also had a placer submittal to examine and evaluate.

A Dime a Dozen


Placer claims are a dime a dozen in the Mojave, and they are typically worthless—at least in my limited experience. (Actual placer miners might disagree with my assessment, but I'm using the mindset of large, hard-rock mining and exploration companies.) Unlike lode mining claims, placer claims can be increased in size if an association (group of more than one person) locates the claim: The usual 20 acres per lode claim or individual placer claim can be as large as 160 acres in an association placer when located by 8 or more claimants.[1] Association placers can, in other words, cover an entire quarter section, making it possible to cover a lot of ground with relatively few claims, something that was done widely across the lowlands of the Mojave Desert of California in the 1980s (and elsewhere, like Arizona, and elsewhen, perhaps even right now). Many of the placer submittals we received during the 80s were located not only for gold, but also for platinum, an element that is quite rare in the placer settings of the southwestern deserts.
“A degree of skepticism should also be reserved for ores said to contain uncommon metals or minerals. Because of their rarity, these substances may command a very high price and are therefore extremely attractive to the investor. The platinum-group metals including platinum, palladium, rhodium, ruthenium, iridium, and osmium, are the darlings of the swindler. Considering their high unit-value, even minute amounts of these metals appear to be a reasonably good bet to the innocent investor.”
–from Mining Scams, AZGS
In any case, I’m not sure why we were called upon to appraise these particular placer claims, nor do I remember their exact location or size.[2] I did already know a few things about placer deposits—a little—having looked at a number of placer submittals in the California foothills earlier that year. The Mojave placer, however, was different from those in the Mother Lode region of California, being “a dry placer” or “desert placer,” which means they were not located on or very close to any actively running water. Flash floods in usually dry washes, and sheet runoff across the fans during storms had formed the sand and gravel deposits that might (or might not) contain placer gold, but the nearest naturally running water was several miles to the southeast in the Colorado River. (Water in the nearby Colorado River Aqueduct was nearer by half, but was inaccessible to any would-be placer operators, including us.[3])

The Desert Sun


The desert sun glared through the windshield of the truck as if to threaten us with heat stroke or worse, and heat waves rose inexorably from broad alluvial fans and bajadas, countless meandering dry washes, and endless desert pavement. As we turned onto dirt somewhere between Vidal Junction, CA, and Parker, AZ, I wondered what we were getting ourselves into. It wasn’t just the question of evaluating a dry placer property located miles from running water, but also the larger question: What were we doing in the Mojave in June? We drove down the fan, over rocks and by countless jumping cholla, not knowing for sure where we'd end up, not having to meet with the prospector, as one does so often when checking out a submittal. It didn't take long, really, before we found the spot, nearly lost in low, decapitated hills and erratic dry washes south of the Whipple Mountains, buried under  a millennium’s worth of accumulated sand and dust. Dust covers entire mountain ranges in the western Mojave Desert, and it collects on pool tables in towns up and down the Colorado River in the eastern Mojave. Parker, Arizona, is one of those towns. Hopefully we'll stop in Parker some other time.
We had brought extra water with us in 5-gallon containers, including 1 or 2 basic upright cooler types and several clear, collapsible plastic types. The extra water was, at this point, for evaluation of the claims, not for our own hydration, but the extra containers would serve us well as our expedition unfolded. So far we hadn't noticed anything untoward in the flavor of the water, primarily because we had filled our containers north of the NV-CA line, probably in Reno. Desert water can taste absolutely awful.

As property reviewers, we would not only have to determine whether gold was present, but we would have to make some deliberation as to the feasibility of mining by a fairly sizable company. I could think of three scenarios for processing (mining) any placer deposit we found:[4] 1) haul water into the area from the Colorado River or from Lake Havasu to wet-separate the heavy gold from the lighter quartz and feldspar sand and gravel, 2) haul the gold-bearing sand and gravel to the water, presumably the Colorado River, for wet-separation offsite (no doubt requiring further land acquisition), or 3) dry wash the sand and gravels without water. Dry washing using the oldtimers' dry winnowing method is notoriously inefficient at gold recovery and can be totally worthless if not done with extreme care and diligence.
How we get gold in California: winnowing gold, near Chinese camp.
Original in Harper's Monthly, v. 20, 1860; source: Library of Congress (no known restrictions).
Of course there are more current methods of dry washing available than winnowing, if you happen to have some gold-bearing sands and gravels on your Mojave placer claims. I'd look into the Bedrock Dreams website, which shows many possibilities and has a lot of info for the up-and-coming small-time gold miner (hard rock and placer).

The Dry Wash


At the dry wash, we camped in trenches dug by the claim holder. In the “cool” of the evening—when temperatures dropped somewhere between 70º and 85ºF by morning—we panned for gold using the precious water we had hauled in. Because the paved roads of Highways 95 and 62 and the desert-river town of Parker were not so far away, we went ahead and used a lot of our water for panning. We didn't have to save most of the water for drinking, which we would have done had we been camping four hours away—over hot, dusty roads—from anywhere of desert significance: any place with water, food, people, and, preferably, gas, spare parts, and tires (the latter preferences ruled out places like Goffs and Essex)

We were lucky, and our pans showed some color: a few, small flecks of gold almost too tiny to see. With repeated tries, we consistently got 2 to 4 colors in each pan. After we used up our extra water, which happened faster than we had envisioned, we took to dry panning. (It doesn't matter how close you are to town; it's ill-advised to use up all your water. You might need it during some unexpected, unplanned-for vehicle mishap or environmental disaster like a clogged fuel filter, a flat, a washed-out road, or a flash flood. See A Few Rules of the Desert.)

At some point, perhaps out of boredom, we gave up on classic dry panning, which looks a lot like regular panning but with tons of dust. One more time we filled the gold pan with the weakly gold-bearing alluvial sand and threw the material expectantly skyward. The evening breeze blew the lightweight fines toward Arizona—where all Mojave sand and dust aspires to reach—and the heavier material fell back toward the pan. We had reinvented dry winnowing! In theory, we should, after several skyward tosses of material, have been left with a few heavies, some black sand, and a few flecks of gold. We weren't, though; maybe our technique was subpar. Regular wet-wash gold panning requires some skill, but if there’s gold in the pan, even an unskilled person will usually find it—although I've seen newbies mistake golden-colored quartz, gold-flecked biotite, and that common mineral pyrite, AKA fool’s gold, for gold. All of these minerals might fool some of the people some of the time, though with practice or a good course in mineralogy, you should not get duped by any of them. Gold is the only mineral that will shine or look bright golden yellow in the shade. Pyrite pales next to gold, and put in the shade it won’t shine—it becomes just another mineral, barely tinted beyond pale brown, nowhere near the bright golden yellow of real gold. (The exact color of gold depends on its fineness and upon which of several other elements, notably Ag, Cu, Fe, Pt, Cd, might be contained within the gold. These factors will affect how bright yellow or golden the gold looks. And then there's chalcopyrite, not as common as pyrite, but often lying somewhere between pyrite and gold in it's yellow-gold sheen. So it is possible to be fooled. But don't be. A Niton™XL3t GOLDD+ xrf analyzer can be a friend.)

Dry panning and air winnowing hadn't done much besides create a lot of dust and two ravenous geologists. So we put the gold pans away and turned our thoughts toward dinner. The sun was fairly low over the Turtle Mountains to the northwest, and my time estimation method indicated we had about 1.5 hours to sunset. What should we eat? We went ahead and established our Mojave Desert, south-of-the-border-style cuisine of tacos or burritos, with avocado and as much hot salsa and jalapeño as we could stand. This type of food is not too heavy for the heat, and (I’ll swear to this—or ask any desert rat) the spicy burning of the peppers created a cooling effect, something we would really need as our time in the desert progressed. Besides, there’s enough vitamin C in the peppers to fight scurvy, a credible desert plague: Rapid melting of the ice will spoil many vegetables and a few fruits over the course of our stay.

Yeah, we had just arrived in the desert and were still greenhorns, not quite able to call ourselves Mojave Desert rats. Not yet.
A little fooling around with SunCalc produced this reproduction of sunrise and sunset at our campsite (approximate location and date).
As the sun sank behind the Mopah Peaks, I thought about the next day. We'd be moving upslope into the Whipple Mountains proper. We were done with the placer submittal and, back in Reno, would recommend “No Further Work.” Although we didn't really know how large the weakly gold-bearing sands are, we suspecedt that their likely flash-flood origin from upstream copper-gold diggings in the Whipples would make mapping out the gold bars and channels difficult at best.

To be continued...

Notes:


[1] (Read about basic claim location rules here.)

[2] In later years, when working for Former Mining Company, I rarely took on placer submittals; in fact I actively avoided them, especially after one particular submittal (a classic scam) led to a fabricated conflict between our lode claims and the association placer claims of the submitters.

[3] The Colorado River Aqueduct is a 242-mi (392 km) water conveyance in southern California. The aqueduct diverts water from the Colorado River at Lake Havasu (at Parker Dam north of Parker, AZ) on the California-Arizona border west across the Mojave Desert to the east side of the Santa Ana Mountains. The aqueduct is operated by the Metropolitan Water District of Southern California (MWD) as one of the primary sources of drinking water in southern California.

[4] A note about my usage of "found" and "deposit." We knew there were claims for placer gold. We didn't know for sure if any gold existed on the property or in the area. If there was gold in the dry washes, the claim owner had discovered it, not us. We, however, wouldn't think of any gold on the claims as an economic deposit until it had been tested, which usually involves drilling or—especially in the case of placers—small-scale test mining. It's not considered accurate to call a mineral occurrence a deposit until it meets economic parameters and passes mining feasibility studies. It is therefore correct for me to assert that the claim owner discovered the gold, but Northern Mining Company's representatives (us!) might discover a gold deposit.

Tuesday, March 14, 2017

The Roan Cliffs Again, This Time with Some Contacts

After seeing Ron Schott's awesome and enlightening GigaPan of the Roan Cliffs, I decided I had to mark some contacts on the photos from my last post (and partly because what I said or implied about the formations were a little off). To deduce the location of these contacts, I extrapolated from this USGS preliminary geologic map, using the USGS TNM 2.0 Viewer and Google Earth.
In the first photo, it's still a toss-up, imo, as to whether the Tertiary Uinta Formation (Tu) can be seen—but if so, it's way up at the top of the cliff. Most or all of the cliff and most of the slope is underlain by the Tertiary Green River Formation (Tg). Aaaaand maybe there's a bit of the Tertiary Wasatch Formation (Tw) at the bottom of the photo.
In the second photo, there is (probably) just a tiny bit of the lower part of the Uinta Formation (Tu) above the cliffy area, and the reddish-brown foreground slopes are underlain by the Wasatch Formation (Tw). The rest, cliff and slope, consists of Green River Formation (Tg).

Thursday, March 9, 2017

From the Road: Bedding and Talus in the Roan Cliffs of Colorado

Getting back to my October-November road trip (last seen here), I stopped to get some fuel in Parachute, CO, on what was Day 7 of the trip, and I ended up taking a few photos (surprise!), partly thinking that the cliffs show good examples of bedding, and also because I was becoming fascinated by the exceptional talus slopes coming off the cliffs. The first photo is a cliff at a round nose sticking out from Mt. Callahan. The second photo is of a cliff at the southern end of a nose known as Allen Point, a long skinny ridge running about 1.5 miles south of a broader, arcuate area also called Allen Point.
When I investigated this area after my trip was over, I was surprised to find that these cliffs are part of the Roan Cliffs: while still enroute, I thought I was driving along the Book Cliffs. The Roan Cliffs are the cliffs that break south off of the broad Roan Plateau, a large plateau area that extends from Rifle, CO, to at least somewhere north of Grand Junction, possibly bounded on the west by Roan Creek. The Roan Cliffs, however, at least as shown here, encircle a broader area extending westward from Rifle, CO, to the mountains just east of the Wasatch in Utah.

The Roan Cliffs are capped by the Eocene Uintah Formation (which we may or may not see in these photos), and slopes below the uppermost cap are composed of the Eocene Green River Formation. Some of the lower, reddish slopes in the area are underlain by the Paleocene to Eocene Wasatch Formation. You can read a little more about the geology of the area in this USGS Bulletin.

The Roan Cliffs stratigraphically overlie the Book Cliffs, which we'll see later. I'm not sure how I mistook the cliffs of the Uintah Formation and upper Green River Formation for cliffs of the Cretaceous Mesaverde Group, or slopes of the Green River Formation for the usually easy-to-spot Cretaceous Mancos Shale. I can only plead that geology at 70+ mph isn't always spot-on.

Tuesday, March 7, 2017

Tales of the Mojave: A Bit About Northern Exploration Company

I planned to have this descriptive section as part of the last post—the one about being packed and ready to leave town—but this "little bit" grew and grew, and eventually it had to find its own home. I've written lots of little pieces like this; many of these could be hyperlinked from several main posts. This one might most properly go near the beginning of a Tales of the Mojave book.

N.E.C.


Northern Exploration Company (NEC), a famous former international mining and minerals exploration company, had seven exploration offices when I began working there as part of a small horde of young or “junior” geologists in NEC’s Western District. Some of us were temporary summer hands (and many of us, like me started that way); many of us were on year-to-year contracts (me!); and a very few of us ended up with permanent positions in the company. There were three or four permanent geos leading the horde when I began working there; that permanent cadre had expanded to maybe six by the time I left.

When not out in the field, we worked out of one of several office-warehouse complexes scattered here and there in Reno and Sparks.[1] The complexes seemed to have been slapdashed together and often had a few problems; for example, the typical southwest-desert–inspired flat roofs were prone to leak during storms or snow-melt. Our complex—and a nearby complex leased by another, also famous former mining company—was near the Truckee River and so occasionally flooded. The large windows of the office half of our complex faced south across a largely undeveloped area of the Truckee Meadows; these windows caused overheating, especially in winter when the low sun provided unplanned for solar energy. Nonetheless, we had a good setup that included a smallish warehouse in the back with shelves for field supplies, tables for core logging, and rock saws and grinding wheels for cutting and polishing hand samples.

The Western District of NEC was a decidedly renegade district, though at the time renegade attitudes were fairly common within exploration groups based out of Reno.[2] Geologists aren’t ordinarily known for their adherence to rules, and they are especially not known for following pointless and questionable rules sent down from above—an above that was usually either outside the country or east of the Mississippi, the latter being nearly the same thing as a foreign country to those born and bred in The West.


We can argue nearly forever about where The West begins or ends. The Mississippi River clearly constitutes one viable boundary for defining what is east and what is west. The hundredth meridian has also been used as the boundary between east and west; for example, in 1843, Thomas Farnham said lands between the 100th meridian and the Rockies were “usually called the Great American Desert” (Stegner, 1954). Later, Thomas Durant held a “100th Meridian Excursion” when Union Pacific crews passed the 100th meridian in 1866, a goal set by Congress. A little later, John Wesley Powell, writing for the USGS in 1879, recognized the 100th meridian as a line roughly defining the eastern boundary of his “Arid Region,” an area that generally receives less than 20 inches of rainfall per year and encompasses most of the west (by any definition). I think one could also use the Great Continental Divide as the boundary between east and west: All drainages east of the divide would drain to the Gulf of Mexico or the Atlantic. All drainages west of the divide would drain to the Pacific.
Google Earth image with yellow line marking part of the 100th meridian. The meridian cuts several states in two and roughly separates a greener area in the east from a notably browner area in the west.
I usually maintain that the true west, “The West” as I capitalized above, begins at the eastern edge of the Front Range of Colorado. Denver is not inside The West by this definition. (Neither is Boulder, for that matter.)


As mentioned in our main text above, geologists within the exploration offices of the west (however we define west) were often fractious and rebellious, and they were unlikely to listen to anyone from Chicago, say, some muckety-muck who might be sporting a fancy three-piece suit and polished black shoes. (There are numerous stories revolving around entertaining such VIPs.) Denver’s offices were often a little spiffier than those in Reno, perhaps having been influenced somewhat by the fancier petroleum offices in the area. Also, some Denver offices acted as headquarters for the minerals explorations groups of larger companies, and some *were* the headquarters for smaller companies. Consequently, geologists who had the misfortune to be based in Denver often ended up being a little more stilted, a little less rebellious, a little more formal: they were ever-so-noticeably more well-behaved when it came down to orders from above, and they were a little more likely to look at you askance if you decided that a rock-throwing contest was in order before the sampling program began in earnest. (A few were definite leaders as far as renegade actions go—here I’m particularly thinking of some unnamed few during my later years at Former Mining Company. Most, though—well, many—tried hard to keep up.)

The Kmart of Exploration


Our Hughes 500-D in 1978.
The Western District of NEC came to be known, at least to a select few, as “The Kmart of Exploration.” This appellation had been assigned to NEC by a summer hire[3] —Dan, the guy with the Frisbee dog, a black and white Aussie of one variety or another—during the uranium summer of 1979. He said he came up with the epithet after being involved in procuring supplies and provisions for the field largely at Kmart. I thought the nickname—seemingly indicating that the company was cheap—was overstated; after all, each uranium camp[4] had a trailer with space for a full kitchen; an office with drafting area, map storage cabinet, and beaucoup supplies; a camp cook; canvas tents with room for two field hands in each tent; a couple of 1978 4WD pickup trucks, brand new during the uranium summer of 1978; and a Hughes 500-D helicopter equipped with radiometric instruments capable of detecting radiation and breaking it down into the three major source elements, potassium (K), thorium (Th), and uranium (U). I thought our camps and equipment were pretty plush, especially when compared to the archaeological camps my husband frequented.

Much to the head honcho's dismay, "Kmart of Exploration" stuck. Perhaps it was partly our field schedule that made the name stick. We worked eleven and three, drive-on-your-own-time. That schedule meant eleven days in the field, three days off, with the driving time between home and field (and vice versa) being on our own time, not on paid-for company time. Perhaps the name stuck because we were encouraged, if not required, to camp out rather than stay in motels.

Camping supposedly saved gas, time, and money because we didn’t have to drive in to town every morning and evening and didn’t have to spend money on motel rooms. We also bought groceries instead of eating in restaurants, resulting in a lowered food expense. So we typically lived outdoors—in the dirt and weather of whatever area we were working in—for two to four nights; then we were into town for one night to get a shower, to sleep in a cool, air-conditioned motel room, to gas up, to stock up on fresh food, and—most importantly in the Mojave—to stock up on water and ice. Then, back into camp mode we went. I thought there were some flaws to the party line about camping, although I never did an actual cost-benefit analysis. For one thing, those of us who didn't have a permanent camp located somewhere near running water in the higher and cooler reaches of eastern Nevada (a certain lucky few that I was rarely part of) spent a certain amount of time setting up camp every evening. After getting our new camp in order, we made dinner and cleaned up. Then, nighty-night. After waking up in the morning, we tore everything down and repacked the back of the truck. With all the unpacking at night and repacking in the morning, we often ended up rearranging boxes of sample bags twice a day. Because we prepped our own camp and food daily, we were essentially working twelve to fourteen-hour days, rather than ten, with little time to rest or recoup in the evening before falling asleep (on cots or on the ground). Ten-hour field days were de rigueur at NEC. That meant we'd quit camp at 7:00 am, say, with breakfast and camp tear-down already complete, then work in the field until 5:00 pm. Then we'd finally get on to camp setup and dinner making after that. When someone else was cooking your meals and when there was running water available for cooling off and even showers, as in the uranium and moly camps, the hours were okay—long, but feasible.

In the Mojave, they were hell.

To be continued...

Notes:


[1] These complexes were often called "geo-ghettos" back then—although that term would probably not be politically correct now—often because they weren't built all that well in some respects, and also because they seemed to house a lot of geological groups.

[2] We cultivated—or were known for—a semi-outlaw attitude and everyday defiance that was deliberately exacerbated by the temperament of the head honcho in Reno.

[3] We didn’t call our summer employees “temps” until a good number of us moved to Forminco, where "temp" was already in use.

[4] For more about the uranium camps, see this series about the Caliente camp of the first uranium summer (that's what we called them: the first uranium summer, and the second uranium summer).

A Reference


Stegner, W.E., 1954, Beyond the hundredth meridian: John Wesley Powell and the second opening of the west: Penquin Books, 496 p., 1992 reprint. Quote from p. 215-216 of 1992 reprint.

Tuesday, February 28, 2017

Tales of the Mojave: We're Almost Ready to Go

The Road South:


Our story—the 1981 story of Allie and I doing recon down in the Mojave—began in Reno in the spring of the year and ended unexpectedly and abruptly in Needles before the end of June. I no longer remember exactly how long we spent in the east-central Mojave, but we looked at six different target areas—depending on how you count them—and we probably spent at two to five days in each area.
"A beginning is the time for taking the most delicate care that the balances are correct. ...
- from 'Manual of Muad'Dib' by the Princess Irulan"


A Caravan Camper on a white truck
in front of a mine dump in eastern Nevada.
Allie and I left Reno in a dull gray, four-wheel drive Chevy pickup truck topped with a matching Caravan Camper, a type of heavy-duty metal camper shell with carpet kit, similar to the one I have now. We were equipped with an ice chest full of food, drinks, and ice; a 5-gallon water cooler or two; sundry camping gear; assorted tools; one spare tire (only one!); and all kinds of exploration equipment and supplies. We had sample bags and sample books, Estwing rock hammers and rock chisels, triplet hand lenses and little magnets on rawhide straps, and little plastic squeeze bottles filled with a 10% dilute solution of hydrochloric acid (HCl). The acid bottles were usually held tight in leather cases that could be slid onto belts. We also had a carefully stowed glass bottle of non-dilute HCl, so we could make additional dilute acid as needed. (HCl was easy to get back then, and the bottle came meticulously packed in vermiculite within a sturdy cardboard box.)

We had files of topographic maps, geologic maps, published reports, books, and copies of company reports in plastic file boxes that would help to keep everything organized while also protecting it from water and the pervasive Mojave dust. We had Brunton compasses in leather holders, ready to attach to our belts. And we had various mapping paraphernalia: mechanical pencils with black, blue, and red leads; colored pencils; pens and markers; and six-inch C-Thru® protractor-rulers of various scales: 10-50, 20-40, 10-20, and 30-60. We had field notebooks to hold notes and sketches, and we had aluminum clipboards that would protect our maps, air photos, and reports. We carried everything we needed for any particular day’s traverse in Filson® survey field vests[1], on belts, or in backpacks. A geologist, fully attired and field ready, is easily distinguished from desert rats, ranchers, and routine hikers.

We also had a pile of camping and cooking gear scattered in the back of the truck: pots and pans; plates, bowls, and utensils; a gas Coleman stove and fuel for said stove; sleeping bags and sleeping pads; a tent, which we didn't use while down in the Mojave; a tarp or two; and other miscellany. We may have rustled up some of the gear from a stash in the company warehouse—though had we not been timely in choosing gear (and we were late that year), we would have been out of luck. A certain person's name was used to describe what happened if you didn't grab your gear in time, or if you got stuck with second-rate supplies. Had his last name been Gibbs, it would have been called "getting Gibbsed." 
U.S. 95, looking south, just a few miles north of Beatty.
Before leaving Reno, we spent a little time pondering two particular questions: 1) should we take a thermometer and 2) should we abstain from beer and other alcohol? We debated back and forth about the thermometer and finally decided to leave it behind. Maybe we'd feel cooler if we didn’t see the expected 3-digit Fahrenheit temperatures!

If the creosote has bloomed, the field season is over.
Speaking of temperatures, when we got to our first locality, the temps we encountered didn't seem too bad, though it took a little time to adjust after coming from the higher and cooler elevations of Reno. We adapted. We devoured lots of fresh fruit. For lunch we’d have half avocados, their centers filled with Italian salad dressing, and we’d roll whatever else came out of the icebox in flour or corn tortillas.[2] We also prepared our own variant of south-of-the-border food, using lots of hot peppers, gobs of hot sauce, and unlimited spicy guacamole. We figured there would be something medicinal in mixing the spicy fire of the food with the scorching heat of the desert. And in fact, these were the only foodstuffs we could bring ourselves to eat in the heat. And throughout the day, from sunup to sundown, we drank gallons of water, juices, and sodas—and zero beers.

To be continued:

Notes:


[1] It looks like the standard survey vest isn't being made anymore—at least I don't see it on the C.C. Filson website. Perhaps that's because so many geos are now wearing safety vests much of the time. I hope my current beige style-12 and orange style-8 vests will last indefinitely: I still use them on field trips, while hiking, and on most sampling and mapping excursions. My beige vest is partly held together by duct tape; a gaping hole in the lower right area developed after carrying a leaky acid bottle inside the inner pocket. (I really don't like having things hanging from my belt, though I did used to wear my Brunton that way. Now I stick it in one of the side pockets.)

[2] This was called a "Bill Rehrig" lunch, although we didn't use that term until many years later.

Thursday, February 23, 2017

Repost: Here's to You, Geological Heroes

My DSL lines and WiFi, provided by Frontier (or not provided, as the case may be), are currently quite lousy with 50%-plus packet loss. For some reason, Google pages and products, including this blog, work at least slowly and sporadically, as does the NWS weather site. So I can find out how many calories I'm eating (or drinking) while checking out the latest atmospheric river that has most likely been one of the culprits in decimating my internet connection. I can also do a little research by asking Google questions and submitting search terms. If the answers show up in the blurb accompanying the resulting list of search results, then I'm good; if not, I'm stuck with a list of websites that won't open. Consequently, I can't quite finish the current post I'm working on: It needs a little more research. So I'm reposting a post from 2010: a submittal to the now defunct Accretionary Wedge blog carnival. Here it is.



The Accretionary Wedge is coming up soon, so my thoughts are naturally turning to Geological Heroes, the topic of this month's Wedge, hosted at Mountain Beltway by Callan Bentley. Callan says,

I invite all participants (geobloggers and geoblog readers alike) to contribute stories of their heroes. It’s time to pay tribute to the extraordinary individuals who helped make your life, your science, and your planet better than they would otherwise have been.
As far as geologic heroes go, I was first thinking that maybe I don't really have any (or maybe I just don't have many personal ones that I feel I can write about on the blog). I thought, therefore, that I'd list two geologists who are heroes to me, although they aren't personal heroes:

  • Tanya Atwater - a leading plate tectonicist, geophysicist, geologist, and oceanographer. She is a hero to me by way of being a leading and famous woman in my field (or a related field), one who "is especially well known for her works on the plate tectonic history of western North America, in general, and of the San Andreas fault system, in particular...."

    I've not yet had the good fortune to meet her, but long ago (and not very far away) I named a dog belonging to my previous partner and me after her. Upon hearing of this dubious honor from an acquaintance of ours, Tanya A. reportedly said, "Ruff ruff," while making a motion like scratching her ear with a paw.
  • Tom Dibblee - a legendary field-mapping man, who mapped "565 quadrangle maps covering over 40,000 square miles, some fourth of the State of California." I first learned of his mapping while working in the Mojave, where his maps cover nearly every square inch of ground and provide the basics and details for every geological map that has come after him. He is known in that region for not having to use a Brunton to take strikes and dips (except when beds were dipping at shallow angles), because his sense of orientation and angle estimation were excellent, such that he was always within a couple degrees. He started mapping when in high school, and never stopped, completing a mapping career of almost 80 years only when he passed away in 2004.
Beyond these two, I was sitting out on the rig one day, and while thinking that I'd just leave this post at a two-person list I realized that the topic "Heroes" was making me think of Waylon and Willie, and I started singing "Mamas Don't Let Your Babies Grow Up To Be Cowboys."

Don't let 'em pick guitars and drive them old trucks...
[technically a road song because it mentions trucks] and then that somehow led me into "All My Heroes Have Always Been Cowboys" followed by "Waylon, Willie, and Me."

Now, not all the lyrics of these three songs are applicable to whatever particular feeling they engendered in me on that recent field day, nor are all of the lyrics particularly applicable to the topic of geological heroes — except that:
When I start thinking about the real geologist heroes I've known over the years — whether male or female — they are rather much like cowboys, or like outlaws: out in the field all day, bouncing around in pickup trucks old and new, doing their own thing, making it on mottos such as "it's easier to get forgiveness than permission" or "it's all changed now," running their own programs, districts, and companies, shooting cans, rolling boulders, and participating in other shenanigans that shall go unmentioned here, some of which have involved various forms of (legal in Nevada) explosives.

These more personal heroes of mine include my thesis advisor(s), my major professor, the professor I T.A.'d for, several former professors and T.A.'s, many geologists from both Northern Exploration Company and Former Mining Company and elsewhere, the two Larry's, the two Nancy's (you *know* who you are), most of my former field assistants — one has or is now running her own company, one patented her Hg-gas sniffing method and has run her own lab, one is now running her own exploration group at a major mine, and some have gone on to other things but are nevertheless heroes to me for making it in the "man's field" of exploration and mining geology.

My heroes, over the years and decades, have also included several FOP/Quat people: JODavis, Bud Burke, Marith Reheis, and anyone who was present for the flying Vee in the middle of the Black Rock Desert in 1987 or who made it to the 1991 FOP down in Fish Lake Valley, Nevada.

And then there are some true outlaws or aspiring, wanna-be outlaws — hmm... should these names go unmentioned? (You know who you are: R, BS, JS, PG, S+D, et al.)

Really, when it comes right down to it, there are too many geological heroes to list, refer to, or name, including all the consultants and independents attending the hospitality suites and receptions at Northwest every year, going back to the wild S+D bashes in Spokane some thirty-plus years ago.
And so, here's to you (all of you)...
...from a copy of a print from an original slide taken here at a now burned-down hot spring cabin, by JODavis in the fall of 1981, photo credits to JODavis and LLLackey, photo ©2010 Looking for Detachment, all rights reserved, poem written by SH and CR.

The Spencer Hot Springs cabin, with roomy concrete bathtub and piped in hot water, was burned down later that year or the next, reportedly by the same individuals who, in their over-zealous righteousness crossed out in red marker the name "Asshole" (and other cuss words written on the interior of the cabin) — these individuals were apparently disturbed by the existence of such a den of iniquity as a hot spring where people *gasp* sometimes bathed naked. I don't know who these red-marker people were, nor do I really know that they were the arsonists — but that's the way the story goes.

The original from the 1978 album "Waylon and Willie."

April 2010 Accretionary Wedge: Heroes

Tuesday, February 14, 2017

Tales of the Mojave: An Intro

Intro


I'm going to move into what I hope to be the blog-publication of a few of my old stories, which I began here quite a while ago with several posts that became the Caliente series and other posts that were part of my Finding a Thesis series (which I haven’t finished). I'm not sure how far I'll get into this new project, but it's something I want to start in order to see how my writing has progressed from the first drafts, which I probably began in the late 1990s. I'll no doubt be interspersing this Mojave set of posts with other field notes, road trips, or miscellany like Friday Fault/Fold, etcetera; we'll just have to see how it goes. Also, at this point the old stories have become tied up with some fictional stories or novel I've been playing with. The fictional book or novel doesn’t really have a plot yet, and it also has a lot of completely made-up to deeply modified or wildly intertwined adventures. I'm attempting, here, to remain true to life.

The Mojave


You can check out any time you like,
but you can never leave.[1]

My memory of the Whipple Mountains, where we'll be heading shortly, extends back to 1981, when Allie [2] and I conducted some preliminary geologic reconnaissance (recon) during June for Northern Exploration Company (NEC). It was my first visit to the Mojave Desert of southern California. (I can’t speak for Allie, but I think it was hers, also.)

The Mojave Desert is outlined in red.
Image courtesy USGS, modified from here.
Hell, that's not strictly correct. Looking back carefully, I really can't say that I had never been to the Mojave before 1981—though I do often say that very thing, not usually thinking about the technical boundaries of the Mojave The boundaries, right, largely though not completely faithfully, follow the range of that well-known Mojave denizen, the Joshua tree.

So when did I first visit the Mojave? Well, let me think. Sometime in the late '70s I was in Vegas for an archaeological conference—we had driven all night to get there and had beheld a truly spectacular thunderhead near Tonopah. Before that, I’d seen (and drawn and photographed and summarized) the Charlie Brown Outcrop during the third field trip in Larsen's Geology of Nevada class. On the way down to the Charles Brown Highway, we had camped in the Beatty dump on Thanksgiving night after a particularly mediocre meal at the C-rated Exchange Club. Fortunately for everyone involved, there had been plenty of beer afterward to settle the stomach.70

Beatty is technically just inside the Mojave Desert, and the Charlie Brown Outcrop isn't far from its center. So yes, using almost anyone's definition of that southern desert, I had been there before '81. Nevertheless, I usually think of June, 1981, as my first foray into the area, and indeed it was the first time I had been south of Shoshone on the California side or south of Vegas on the Nevada side...

Our Carryall probably had 4 doors.
Photo credit: CZmarlin.
No wait! Most maps place Baghdad, Arizona, in the Mojave, and I'd been to Baghdad during field camp in '73; that was the place we'd gotten a Carryall stuck in the sand while trying to take a short cut back to Flagstaff. We weren't even supposed to have gone that way, but we'd purposefully drifted to the rear of the caravan and then left the pack. It had taken us an hour to dig out. We had finally made it back to Flag for dinner, only to find that no one had even missed us! The mishap instantly became one of the highlights of field camp, albeit one with apocryphal overtones: We exaggerated our difficulties while building road to get unstuck, we gleefully inflated the story during the two-hour drive back to Flag, and we greatly hyperbolized the event while telling the story over beers later that evening.

This little spate of reminiscing has brought me to the realization that I still don’t always think of the Mojave by its technical definition, and that in 1981 I generally thought of the Mojave as a big hot unknown encompassing the entirety of the southern California desert, or at least the part of it that lies south of the Garlock Fault. Back then I often thought that the SoCal areas north of the Garlock, including the broader Death Valley region, belonged to a kind of never-never land that should really be part of Nevada. I still often think the CA-NV border should run along the crest of the Sierra, though I’m not sure where that line should jog eastward to leave the main bulk of southern California in California, and somehow place Clark County of Nevada in SoCal.[3]  Perhaps the new border would look something like this, with the CA-NV border in white, and the southern CA border in yellow:
Google Earth image with proposed new borders.
Later in my career—later being when I worked at Former Mining Company, AKA Forminco—we, the southern explorationists of Forminco's Western District used the presence of cholla as a key factor when trying to push our district north into Nevada, as far north as the Gilbert mining district in the Monte Cristo Range northwest of Tonopah. The Nevada District had responded with uncharacteristic equanimity and had let us in, mostly because they didn't really want that part of Nevada.
Anyhow, back in the early 80s I liked placing the northern boundary of the Mojave at the Garlock Fault: It made geographic and geologic sense to me at the time, and it affirmed a feeling I had, when driving south across the Garlock, a feeling of dropping off into another, lower land. And as far as I was concerned, the eastern boundary of the Mojave was the Colorado River. My boundaries, however, held as little water as most Mojave washes—for one thing, there really isn't an elevation drop when driving south across the Garlock along U.S. 395 or S.R. 14, and even though there is quite a drop when coming into the Mojave from the west at Tehachapi, one has at that point crossed the southern Sierra Nevada, so a drop is to be expected; and for another thing, the Mojave is really defined as more of an ecologic or biologic-climatologic region than a physiographic region—and I knew that, so I always spoke of the "Mojave Desert of California" when referring broadly to all of the southern California deserts, or even those just south of the Garlock, hoping that the phrase would exonerate my technical sloppiness.[4]
Google Earth image showing part of the western Mojave, a bit of the Garlock Fault (dark blue), and U.S. 395 and S.R. 14. Ignore the road marking for 58; it is inaccurate.
This recon program was completely mine. Prior to that summer, the target areas of grass-roots ventures I'd been involved in had been at least partly chosen by others. I did the research in the spring, generating several targets across the region, from Tehachapi to Barstow to Needles[5], and I decided where to start. We'd begin in a few relatively low areas along the Colorado River—the district boundaries of NEC were such that someone else was in charge of Arizona, so like an aquaphobic saguaro in reverse, I wasn't supposed to cross the Colorado River—and we'd work our ways toward higher elevations, hoping to get ahead of the summer heat.

Because of a delayed start to my recon targeting, it was late in the field season, probably the first of June, when Allie and I finally left Reno to drive as far south as Parker, Arizona. I wondered how long we'd last down there in the heat of early summer; we knew it wasn't the most auspicious time to begin field work in the Mojave, but we hoped we could stick it out and find a property or two to stake.

My first recon program! I was both excited and apprehensive.

To be continued...

Notes


[1] Felder, Don, Henley, Don, and Frey, Glen. "Hotel California" (lyrics) perf. by the Eagles. Hotel California (album), Asylum Records, 1976.

[2] Names have been changed.

[3]Northern boundary of Southern California, at Wikipedia.

[4] In reality the Mojave Desert is an ecologic area defined by plants and climate, which extends as far north as Beatty, Nevada, and which doesn't include all of southern California's desert, because some of that area belongs to the Sonoran Desert. Whether the Whipple Mountains is in the Mojave proper seems to depend on who draws the map. These stories will take place mostly in the deserts of southern California, and I'll usually refer to that area as "the Mojave." 

[5] A target area can consist of a whole region (like the Mojave Desert itself), an entire mountain range (like the Whipple Mountains in the eastern Mojave Desert or western Sonora Desert), a large or small mining district (like the Savahia Peak area in the Whipple Mountains), or a smaller area around one old mine or prospect (like the Dollar Bill Mine on the south side of Savahia Peak.).

Tuesday, February 7, 2017

From the Road: Talus Stripes and Shorelines along the Truckee River

Talus, shorelines, and fall colors.
It was a late fall day, and I stopped along Route 447 to see if I could get close to some of the brilliantly colored trees along the Truckee River a few miles north of Wadsworth. I didn't end up finding a good spot for pics of fall colors—other than maybe this one taken down near the Numana Hatchery—but I did find lots of wonderful talus stripes and some Lake Lahontan shorelines.

At two stops a little farther to the north, at and near the junction of 447 with Chicken Road and at the Historic Marker 448 pullout, I grabbed a hodgepodge of photos.
Looking SSE from the historic marker pullout.
These two photos look south-southeastward along the Truckee River toward distant Fernley. A good portion of the river in this area runs parallel or sub-parallel to Walker Lane strike-slip faults. Wadsworth Amphitheater, which shows up in the Google Earth images we'll see in a minute, is not visible from any of our photo sites; it's an amphitheater-shaped topographic feature cut into Lake Lahontan sediments right along the east bank of the Truckee, beyond the dark basaltic hills on the right side of these two photos (east side of the Truckee).
I love the lone Cottonwood in this photo.
I went ahead and drew a few lines on Google Earth, then I rotated the resulting images to two different orientations so we could see a little more of the terrain. Be sure to check the north arrow in the upper right! The linears I drew are parallel or sub-parallel to the trend of the Walker Lane. You might be able to pick out a few more in the images (or go to Google Earth and looking around a bit).

The Walker Lane—on Google Earth (G.E.)and on other aerial representations such as air photos—shows up best at very small scales; that is, if we zoom way out and observe the area from way above, we can see the trend of the Walker Lane better than if we zoom way in, like we've done here. Nevertheless, individual strike-slip faults have been identified throughout the Walker Lane, and a few of these occur right in this area.
The A is centered on Wadsworth Amphitheater. The purple camera icon shows the location of the first photo.
The next G.E. image zooms in to the area we can see in the photos. I've got all three photo locations turned on, the A for Wadsworth Amphitheater, and my drawn-in linears. These linears aren't necessarily faults, although I'm pretty sure the one on the far left is. Unfortunately, because I currently have a very lousy internet setup (thanks Frontier!), I can't load very many research web pages. Google works well—and Blogger is a Google product—so I can blog even with 25 to 100% packet loss (it's 50% this very moment). And because Google Earth is a Google product, it's working for me also! (But I can't routinely access my non-Google email.)

Back to the faults and linears. I do know from personal experience that Walker Lane structures pass through the Lake Lahontan sediments in the area where the Truckee is running in a particularly linear fashion. I know this from some work I did a long time ago with J.O. Davis, who was studying Lake Lahontan and using tephra beds to date various aspects of the stratigraphy. The two linears or faults in the lower right of the image cross through the area where I've seen older Lake Lahontan sediments faulted and highly contorted by the major structures that pass through the area. I can't say that my particular linears are right on the major structures, and I can see other possible lineaments.

UPDATE 3Feb2017: I now have good internet back, and I've been able to compare my "map" to a geologic map of the area (Bell, Garside, and House, 2005). My linear passing through the hatchery location (below) is spot on for their most prominent fault, which was mapped as a dominantly extensional fault.
A zoomed in G.E. view of the area.
Not sure why, but I prefer to spell amphitheater with an "re" at the end: amphitheatre. I also have a hard time sticking the first "h" into the word!

I sure wish Frontier was a better internet service provider! (I never had this kind of semi-routine trouble with AT&T in eastern and northern Nevada; their every-day speeds were faster, and service was (generally) provided more quickly.

Back to the photos! 😊
Horizontal Lahontan shorelines and vertical basaltic talus stripes.
Some of the same talus stripes in Google Earth.
This photo shows a juxtaposition of talus stripes, faint shorelines, and layered Lahontan sediments.
On this trip, I focused mostly on trying to get good photos of the talus, because that's really what caught my eye. I later noticed that a few shots showed the Lake Lahontan sediments fairly well.
White, gray, greenish gray, and pinkish layers of the Eetza Alloformation.
While driving through the area, I'd been assuming that the prominently exposed white units were part of the Sehoo Alloformation. I was wrong! The Sehoo is barely identifiable in this zoomed in photo, and it's the older Eetza that is most conspicuous. In fact, the Sehoo here is mapped as gravelly beach deposits, so it mostly comprises the dark gray or brownish gray layered deposits above the whitish units.

Note: I usually use "formation" when talking about the subdivisions within the Lake Lahontan section, but "alloformation" is technically correct. In explanation, Bell et al (2005) say this, "Lake Lahontan and related subaerial deposits were considered lithostratigraphic units in the early studies of Morrison and were designated as formations. With the revision of the North American Stratigraphic Code in 1983, new allostratigraphic and pedostratigraphic unit definitions were added which allowed the definition of time-transgressive, lithology-independent rock units and soils."
Qsm = middle member of the Sehoo Alloformation; Qe = Eetza Alloformation.
After taking all these photos, it was time to move on, so I looked to the north, in the direction I'd be heading.
What I saw was more talus, more shorelines, and more Lahontan sediments. (And some fall colors.)
Selected Reference:
Bell, J.W., Garside, L.J., and House, P.K., 2005, Geologic map of the Wadsworth Quadrangle, Washoe County, Nevada: Nevada Bur Mines and Geology Map 153.