Geology on the Road: Highway 50 #3

Keystone Junction, Nevada, Revisited:

The fault and fold exposures described earlier, are right at Milepost 62, on the east side of Highway 50, just south of Keystone Junction.

The geology of the region is complex, and origin of these outcrop-scale folds are not understood by myself at present. Low-angle faults in the region are often taken to be low-angle normal faults, especially in the Egan Range north and south of Highway 50, and also especially to the east in the northern Snake Range (I'm skipping the intervening Schell Creek Range, here, which also has many low-angle faults).

The regional map of the area - in NBMG Bulletin 85, Geology and mineral resources of White Pine County, Nevada, Part I: Hose, Blake, and Smith (1976) - shows all low-angle faults as "low-angle faults," not distinguishing between reverse or normal faults. A more local map of the area -USGS Quadrangle Map GQ-1085, Geologic map of the Ruth quadrangle, White Pine County, Nevada: Brokaw, A.L., Bauer, H.L., and Breitrick, R.A. (1973) - shows the faults near Keystone Junction as "thrust faults." Both maps were published prior to general acceptance that many of the low-angle faults in the region are extensional in origin or detachment-related.

In the above portion of the Ruth Geological Quadrangle Map, the bright pink "Try" is described as middle Tertiary rhyolite flow and intrusive rock , the red "Km" is described as Cretaceous intrusive rock of 103 to 123 Ma. The purple "MPe" is the Ely Limestone, of mostly Pennsylvanian age.

I don't really know about these particular faults, and I don't really know about the folds, either! The authors below describe and discuss the extension in the region and in the immediate area.

Gans, et al
Gans
Seedorf and Maher
many others

I have not found much in the accessible online literature pertaining to thrust faults in the eastern Nevada region, although the older literature refers to all low-angle faults in the area as thrust faults. Peter Misch was key in recognizing or describing many of the low-angle faults of the region - some of the history of his work is described here. This eastern Nevada area generally lies between the Central Nevada Thrust Belt (of Paleozoic age) and the Sevier Fold and Thrust Belt (of mostly late Mesozoic age). Here is some info about thrust faults, including a diagram showing the location of the Sevier Thrust Belt; another diagram here gives a more generous width to the thrust belt.

And then there's the Jurassic "Elko Orogeny"...