Tuesday, April 5, 2016

Death Valley Trip, Getting There: A Jeep Trail, Folds and Cartoons of Folds, Even More Folds, and Boundary Peak

An unnamed portion of the Gabbs Valley Range.
From the vantage point of the end of the last post, a little southwest of Luning, Nevada, I turned around and pointed my camera northeast across Soda Spring Valley ... and paused to think back to the late 1980s, when we in the Western District of Former Mining Company had finally taken over exploration of the Walker Lane, which until then had been a mostly unexplored part of the Nevada District. We drove all the roads in the area—up canyons, over ridges, and across saddles—and one thing I remember in particular was coming over the top of a low ridgeline from the east, on a jeep trail that dived and went into a series of moderately sharp switchbacks as it approached some old mine workings.
The road in question is below the arrow.
Ah yes, the memories. We found a gold-bearing skarn—it's not quite in view in the photo above—and after some sampling and sketch mapping, we debated targeting some drill holes, but decided it was too small for our target size.

Back to the road itself. Coming over the top from the east (something I'm not likely to do in any near future that I am aware of), the road immediately drops and dives around a curve, making it hard to judge the condition of the road ahead. We maneuvered to some particular point and stopped. What the H! We would have to do a bunch of walking to actually explore the area anyway, so maybe it would be better to stop here at this turn-around spot than to go farther and find that the road requires backing up on steep slopes around sharp turns.

I don't really remember how we handled the sampling logistics. Sometimes it's easiest to drop a couple people off near the top and then meet them at the bottom later in the day, after they've sampled the upper slopes and you've sampled the prospects in the lower hills. Or maybe after a bit of walking around, we found the road acceptable and drove on down.
The road as seen in Google Earth. It's downhill to the lower left (SW).
The Google Earth view of the road is somewhat impressive *in* Google Earth; here's the Google Maps link in case you want to find it on Google Earth.

The view from the upper part of the jeep trail was grand. I've tried below to simulate the view by sloppily stitching together two Google Earth images:
Walker Lake is off in the upper right (W), Luning is just left of center on the other side of the beige plain (SW); Mina is out of the picture to the left (S). 
After grabbing the first shot or two, I pointed my camera more to the east—a little north of east, to be precise—at a folded part of the Gabbs Valley Range, another area we explored back in the late 1980s.
The notable landmark of this part of the Gabbs Valley Range is a dark pimple of a peak to the right of center: Volcano Peak.
Volcano Peak is not a volcano; rather, it is underlain by tilted beds of the Upper Triassic Luning Formation, which consists mostly of limestone, dolomite, and shale.
Zooming in, we get a better view of Volcano Peak and can identify a few old porphyry copper drill roads that probably date back to the 1960s or 70s.
In a similar Google Earth view, we can begin to see a fold nose, centered and just above the dark line (a Google Earth artifact).
I've cropped this image so I could zoom in farther. The upper drill roads are more apparent. Volcano Peak is now on the far right.
It can be fun to take a shot at the geology by drawing lines on photos like these, or on air photos. Drawing without checking the geology first can be chancy, if one is concerned about being right, as can drawing without checking the geology in the field afterward.

Before checking the geology, I came up with the following cartoon, wherein I assumed many features to be stratigraphic beds, and assigned a few other features to faulting.
Here's my first cartoon, with presumed bedding in cyan and a few tentative high-angle faults in dark purplish blue.
I wondered if the central dashed line across the first cartoon was a low-angle fault of some kind.

After concocting the first cartoon, I checked out the geology as mapped by Ekren and Byers in 1985. It turns out that I missed a large blob of quartz monzonite (mapped as JKqm).
The quartz monzonite is outlined in red.
The central line, which was dashed in cyan in the first cartoon, has now been drawn in dark blue, a mapped fault. It's a high-angle fault, however, and it's just our angle of viewing that makes it look horizontal. (Here we can see why apparent dip matters so much: from this angle, the dip looks to be nearly zero; in reality, it is closer to 90 degrees, although that's a guess, as there is no measurement of it on the geologic map.) The quartz monzonite is cut by this high-angle fault, which is down-to-the east, dipping eastward away from us. I left in the cyan bedding emphasizing the fold, and I left in my still tentative high-angle faults in dark purplish blue (toward the right).

These two cartoons show the problem with assuming too much from photos (or air photos). Features that look like bedding might, when field checked, actually be faults, dikes, or other structures like joints. In this when case, we checked the cartoon against a geologic map of relatively small scale, 1:48,000 or 1 inch = 4000 feet.

Somewhere in these canyons, way back in the late 1980s, we came across an old, partly broken-down core shed. The shed was mostly intact then, but the core had started to become scattered, either from vandalism or from the escalating disintegration of the core boxes (or both).

By this time on our trip to Death Valley, it seemed that we should be farther along, but we hadn't even gotten to Tonopah! So we moved on, but almost immediately we decided to stop not far down the road: it was getting to be lunchtime. Just before Mina, we pulled off the highway onto a major dirt road that goes eastward between the Gabbs Valley Range and the Pilot Mountains.
Looking southeast toward the Pilot Mountains from a broad alluvial plain above the town of Mina. Pilot Peak is hidden from view behind the unnamed, lightly snow-dusted, >8500-foot-high peak.
A lot of folding, thrusting, and possibly some low-angle normal faulting has occurred in the Pilot Mountains. In fact, the area is (or should be) one of the type localities for the Luning-Fencemaker fold-and-thrust belt.

While eating a cheese-bologna sandwich, I took a few photos of some of the folds. Some recumbent folds are actually better viewed from another road, but I forgot about that until looking around in Google Earth.
Folds! This is probably mostly Luning Formation limestone and shale, with some Tertiary volcanic rock in the lower left.
More folds!!
The potential here for great fold photos only increases with time spent in the area, and driving up into the hills would do the same.
I turned away from the folds to take this shot of Boundary Peak.
I grabbed this photo of Boundary Peak, hoping that MOH and I would get even closer later in the trip (and we did!). The photo shows both Boundary Peak (the highest peak in Nevada) and the higher Montgomery Peak, which is right behind it and slightly to the right in this photo—look carefully!

We'll continue our journey after lunch. We'll be stopping at Redlich and the Boss Mine. We'll see desert pavement and a cholla. We'll see Boundary Peak again. We might spy some breccia and a solar power plant.

Location map

Related Posts (in order of posting):
Death Valley, "Super" Blooms, Turtlebacks, and Detachments
Death Valley Trip, Part 2: More of the Badwater Turtleback Fault
Death Valley Trip, Part 3: Northward, and over Daylight Pass
Death Valley Trip, Getting There: Wave Clouds beyond the Sierra
Death Valley Trip, Getting There: A Hike to Pleistocene Shorelines
Death Valley Trip, Getting There: Walker Lake, Road Stories, A Bit about Copper, and Some Folds near Luning

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