Coarse-Grained Calcite in the Devils Gate Breccia

I just realized that I meant to include one of these photos in the main post about the breccia at Devils Gate, near Eureka, NV. Instead of one extra photo, I hereby give you three.

The matrix between the dark gray limestone breccia fragments consists of coarse-grained white calcite, with the calcite crystals intergrown in a fashion that I've not seen before.

Here's a photo zoomed in on crystals near the tiny bush in the previous photo. This time my boot barely made it into the photo.

ENE of Center: Breccia at Devils Gate

About 35 miles east-northeast of The Geographic Center of Nevada, both Highway 50 and Slough Creek go through a gap in the south end of Whistler Mountain, a gap or notch known as Devils Gate.

Note: Devils Gates are scattered all over Nevada, including a second Eureka County Devils Gate located north of Eureka, west of the paved road between Eureka and Carlin. Our Devils Gate, the one in this post, is located about ten miles east of Lone Mountain and seven miles northwest of Eureka (MSRMaps location).

Coming into Devils Gate from the west just before sundown.

A large breccia can be seen high on the carbonate cliffs north of Highway 50 when you approach the gate from the west. MOH and I first noticed this breccia several months back; we pulled over to check it out with binocs, then mosied on, filing the place away for a future hike. Finally, coming back from Serbian Christmas, the time was right.

We pulled off the highway onto a little dirt entryway that accesses the old highway south of the main road, parked the truck, and started walking. By the way, we've had the Prius on this old road, so presumably the pullout is suitable for most vehicles. After making it across the highway, we walked down a rabbit-brush infested two-track road, crossed Slough Creek, and then bypassed a fence by walking over to its abutment against the cliff face.
As we skirted around the base of the cliff toward our goal higher in the cliffs, we made a discovery: we found a lower breccia associated with small caves and solution cavities. In the photo above, the upper, larger breccia is in a smallish, bright white patch in the far, upper left part of the cliff; the lower, smaller breccia is clearly visible in the lower right of the photo, closer to Slough Creek.

This labeled Google Earth image shows the location of the upper and lower breccias and our convenient pullout. Re: pullouts, YMMV.

The lower breccia, shown above, is easier to reach than the one high on the cliff, and is recommended if you don't feel like scaling the hillside. The lower breccia contains some large, generally elongated and subrounded carbonate breccia fragments in white calcite cement of varying thickness. The thicker, upper part of the white calcite looks vein-like to almost bedded.
Our goal, the white patch with one conspicuous dark gray fragment, is now obvious in the center of the photo.
Side-hilling up this scrabbly, brushy, talus-covered slope was tricky in places, especially where talus formed only a thin veneer over the bedrock, and where limestone beds jutted out unexpectedly, sometimes forcing a downward retreat.

MOH, on a ledge to the left of the breccia, provides a bit of scale.

This is a large breccia body with large fragments, somewhat remindful of the Titus Canyon breccia in Death Valley, though not as complex. The large to giant fragments are angular to subrounded, and are set in a matrix of coarsely crystalline white calcite. The breccia body, as exposed, appears to be mostly in one or two layers or beds of the Devonian Devils Gate Limestone; its shape could be subspherical (possibly cavern-like) or cylindrical (pipe-like).
Nearly the entire cliff face in this alcove is composed of breccia. For scale, the dark olive green ephedra bush near a curved breccia fragment (right of center) is about 3 feet high. Also, see the next photo for a closeup of the curved fragment and the same bush.
The curved fragment behind the ephedra bush shows primary layering or bedding, as does a second curved fragment below it.

Vertical to overhung cliffs of Devils Gate Limestone are towering behind me in the next shot, and I'm having trouble finding solid footing in the talus-ridden alcove. Talus was almost slithering down the slope, about to cascade over cliffy beds of limestone to the tear-a-pants rocks below. No boot-skiing allowed here, unless you know how to ski jump.
The breccia is mostly exposed in this one wall. The alcove may have formed from erosion of breccia; maybe it formed from erosion of solution caverns or caves no longer apparent and partly associated with the breccia. Here, I'm just speculating, as I don't really know the genesis of the breccia or the alcove. The curved fragment from previous photos is now above the 3-foot high ephedra bush and to the right, below and to the right of the large central fragment. From this angle, the curved fragment looks oval. Numerous smaller, angular pieces of dark gray limestone float in white calcite below it.

The ephedra bush suggests an apparent height or thickness of 20+ feet or 6+ meters for our breccia, but viewing angles are deceptive in the alcove.
Fragments are clast supported to matrix supported. One example of matrix support can be seen in the upper part of the cliff exposure, where the mass of calcite appears to be greater than the mass of fragments. It's possible that solution caving caused collapse of pieces and large blocks of limestone, which then concentrated toward the bottom of the collapsed area, leaving the upper area partly open after collapse and before later calcite deposition or infill.

The white breccia matrix consists of large, intergrown calcite crystals. White calcite veinlets in some fragments appear to be mostly, but not entirely, older than than formation of the breccia, and therefore older than the white calcite infilling event. I noted only a few places where late calcite veining appeared to cut across both the breccia fragments and its coarse calcite cement.

The age of all this activity — breccia formation, fragment cementing, and early and late calcite veining — is unknown to me.

An unidentified plant grows on coarse-grained white calcite in a narrows below the alcove.
Update: Identified by Hollis in comments as Petrophytum caespitosum.

Here's some more coarse-grained white calcite with a nicely reflective calcite crystal above my boot.

NOTE: More pictures of the calcite matrix can be seen here, along with one more shot of the petrophytum.
The same unknown plant is growing on dark gray Devils Gate Limestone in the ledgy area outward from the alcove.

We take one last look at the breccia before starting downhill.

The view from the ledge, looking west: Highway 50 and the partly parallel old highway angle across in the upper left; Slough Creek, surrounded by lots of rabbit brush, meanders through the foreground; Lone Mountain stands alone in the distance.
After making our way downward on some decent, though imperfect, boot-skiing slopes, we looked back at the breccia and wondered if the way we came down would have been easier as a route up than the scrabbly sidehill across loose talus.

Top 10 reasons I love detachment faults / core complexes

Not sure about the order of these things, but here's a go at the geoblogosphere's most recent spontaneous meme, as started by Erik Klemetti, and followed by Siim Sepp and Callan Bentley. Oh, and by the way, I also love volcanoes, sand, and structure — among other geologic subjects and subdivisions — not necessarily in that order.

* They are not everywhere. Detachment faults associated with metamorphic core complexes are generally found in a band running from British Columbia, into Washington and Idaho, through eastern Nevada, into Arizona and the Mojave Desert of California, and down into Mexico (and also in other parts of the western U.S. and in other parts of the world). They run through my general neck of the woods, in other words, but occur in rather specialized geologic settings. This is all right by me. (If they were everywhere, we would miss out on other types of geology.)

* Detachment faults are found in Nevada. I love working in Nevada! Has anyone noticed that?

* Detachment faults and core complexes are found in the Mojave Desert. At first I kind of disliked working in the Mojave Desert because, although similar to Nevada in some ways, it isn't Nevada: it's hotter than Nevada, it's dustier and hazier than Nevada, and the mountain ranges are often older, more worn down, and farther apart than those in Nevada. The roads are cruddier, the small towns less inviting or pleasant in many ways (e. g. Baker, CA). You can find some strange people in the Mojave, and the place doesn't seem as safe as Nevada. I gradually grew to like the Mojave Desert, maybe largely for the exceptional geologic exposure, maybe for all it's weirdnesses, maybe because someday, perhaps, Nevada will look more like the Mojave. I also love to hate cholla cactuses, especially ones growing around the Whipple Mountains core complex.

* Detachment faults are often well exposed. Good exposure of detachment faults is, perhaps, largely associated with their general location in areas that have good exposure, but being of regional extent by definition, they consist of large faults that can often be found around or on top of entire mountain ranges. (I love exposure.)

* A good detachment fault is a thing of beauty. It's relatively flat-lying, very smooth, often shiny, and has wonderful slickenlines and grooves all over it's surface, often aligned in a nearly east-west direction.

* A core complex is complex (surprise). Core complexes aren't easy to understand, and every one seems a bit different from it's nearest neighbor. Geologists dispute the formation and development of these things, allowing for great arguments over beers, great field trips and arm-waving sessions, and exceptional reason for practising down-to-earth to wild-eyed geo-speculation.

* Core complexes and detachment terrane in general are good places to study all kinds of geology. I love all kinds of geology for all kinds of reasons. You can find all rock types — sedimentary, metamorphic, and igneous (often plutonic, sometimes volcanic) — associated with core complexes and detachment terrane, along with great structure.

* Core complexes are mega structural features. I love structural geology, and core complexes and associated detachment faults provide excellent terrain for studying all kinds of structure, from mega to micro scales, including often unexpected but sometimes present contractional structural features.

* Detachment faults are a good place to find breccias: microbreccia, chlorite breccia, etc. I love breccias!

* Core complexes can contain ore deposits. Sometimes older ore deposits have been smeared or extended in the lower plate below the detachment fault; sometimes ore deposits are found along the detachment fault in possibly genetic association; sometimes pre-detachment ore deposits have been extremely sliced and diced by the detachment fault and its related upper-plate faults. Exploration for ore deposits is what I do. (Read a few discovery stories here.)

West to Southwest of Center: Beers and Roads and Folds and Things

I thought I'd back up to a time a week before our stop at The Geographic Center of Nevada, a time just prior to our soak at Spencer Hot Springs. MOH and I had gone out to Austin, Nevada, and we had aimed, successfully, to arrive in time for Serbian Christmas.

Serbian Christmas is celebrated yearly at the International Cafe & Bar, and we've happened in once before without knowing that we were arriving on that celebrated date. This time, we postponed our already scheduled trip to Austin by one or two days in order to arrive on the 7th of January, which corresponds to December 25th on the Julian calendar.
By perfect celebratory standards, we got there just a wee bit late, but still in time to get a room with overrated free wi-fi (terrible bandwith, poor broadcasting) at the Mountain Motel, and time to sit in the bar for a drink or two — including some traditional plum brandy from Serbia — before moving to our table in the cafe. The Christmas dinner of pit-roasted pig served with various and sundry dishes and desserts begins at around 2 or 3 in the afternoon (or maybe as early as noon). I think we sat down just before 6:00 and the food was still coming. The meal is free (unless you order off the pizza menu), the experience is more than worth the price, and the cuisine is the best for miles around.

We spent much of the next day trying to find a certain locality in the Northumberland caldera, and at one point we came close to taking the right road.

The right road.
I somehow didn't manage to take a picture of the wrong road.

We found a nice Z fold in Ordovician cherts of the Vinnini Formation just a couple miles southeast of the turnoff to the right road. The Z fold was part of a larger fold or fold complex that was difficult to photograph with straight-down-sun lighting. You can barely make out the Z fold near the main fold axis, just to the right of the prominent, though thin, black chert band in the right hand part of the photo.
Here's a better look at the Z fold with my boot for scale
And here's the Z fold rotated into a Z postion. I'll leave it to all the diehard structural types in the audience to tell me which direction is up in the photo showing the whole fold.

Not knowing that we hadn't made it to our sought-after spot in the Northumberland caldera, we returned to Austin after partaking of the waters at Spencer Hot Springs. We had another beer or two at the bar before eating dinner at the International, and the next day we continued our journey.

View Northumberland in a larger map

One Year Ago Today: Almost Stuck!

The day was dark with rain and snow, but we headed out anyway, thinking that we could visit the museum in the small town of Cherry Creek in eastern Nevada. We made our first stop on the side of the road to check out this large antelope herd. Antelope can often be spotted between McGill and old Schellbourne Station.
Cherry Creek, the town, is located on the eastern range front of the Cherry Creek Range, where Cherry Creek, the creek, comes out of a small gap in the mountains. Structurally, Cherry Creek looks like it's situated where the north Egan Range runs into the Cherry Creek Range, but the northern end of the Egan Range as named is located in Egan Canyon, the next gap to the south (MSRMaps location showing the regional Basin and Range structure).

That's State Route 489 (above) cutting across Steptoe Valley toward Cherry Creek. The parallel white lines along the road in the center of the valley are patches of snow; standing water can be seen south of the paved road. This possibly intermittent lake or wetlands has recently appeared to be contiguous with Goshute Lake several miles to the north. (This year's so far extra-dry winter might have changed the extent of the southern wetlands.)
This is most of the small community of Cherry Creek. The museum wasn't open, the light was flat and dark, and we didn't spend much time looking around.
It could be a nice place to live, if you like beautiful scenery, out-of-the-way places, and long drives to market.
We hightailed it back to the center of the valley, where we decided to drive south along the historic Nevada Northern Railway to check out a boxcar or other railroad-related artifact we could see off in the distance. The road was well graveled and dry to begin with; the yellow line in the Google Earth image above shows our traverse from the paved road southward.
We made it about 600 or 700 yards before deciding not to go any farther. At this point, the road was turning into a watery mudhole, with no end in sight. In fact, we'd already driven breathlessly and unwittingly through mud we initially couldn't see the end of, and we had come to this short semi-dry spot. The rail, just off to the left in those prickly bushes, prevented any turnaround options, so I decided to back out.
Backing out meant going through a long stretch I shouldn't have driven through in the first place, but had started into before I could stop, then kept going through while hoping for a break in the mud and a turnaround spot. You can see the closest mud hole easily, a second, even larger hole beyond that, and a hidden muddy spot between the two more obvious holes.
Looking at this after driving backwards through it, makes it look pretty tame, but the truck kept getting pulled sideways into the deeper parts of my own tracks, while I tried to stay to the side on the dryer ground right next to the bushes. Consequently, we experienced a bit of fishtailing, and my dual tracks look like a mess of incompetent driving.
Backing up even farther, the road looked good as we went in, just slightly muddy.

Mud is a deceptive thing to try to drive through. Often, one can see a weakly muddy road ambling off in the distance, and this light mud goes on far enough ahead that one can easily get started into what turns suddenly, or gradually, into heavy-duty, very slippery, or deep mud. Getting out and walking an unfamiliar road is recommended, but one usually only walks so far ahead before deciding that the coast is clear: let's go ahead and drive! Incipient or weak mud might suck you in (so to speak), then suddenly, just around the corner: OMG! You're suddenly stuck if you stop, maybe not stuck if you keep going, or maybe staggeringly stuck far from solid ground if you keep going.

If stuck in winter, waiting until the big freeze early in the morning can be one way of getting out. Sometimes a longer waiting period (say months until spring or summer) is required, along with heavy equipment (a D-8 or D-9 dozer). With all the large bushes along our road, we would have been able to build a road under and behind my truck; this procedure often requires multiple jackings-up of the truck (jacking-ups?).

We weren't far from a routinely traveled road, so if badly stuck we could have walked out (in miserable weather) and hoped that whoever we flagged down could have rustled up a dozer: mechanized extraction is easier, though more costly, than building a road by hand. Overall, my getting stuck preferences include better weather (not too hot, not too cold), and I much prefer to be paid to get stuck and unstuck — rather than to be doing it on my own time — a preference come to by many years of off-roading as part of my job.
After backing through the mud, I finally reached a wide point in the road and turned the truck back to the north. An old pump house from the historic Cherry Creek Station is mostly hidden behind the truck; the remains of the water tower can be seen to the right.
We didn't spend much time looking at the base of the water tower at Cherry Creek Station. Maybe we'll go back someday, preferably when the sun is out!