hoodoos, we see that they are shaped much like the "tent rocks" in the Kasha-Katuwe Tent Rocks National Monument in New Mexico, and though close to the ground, they also look a lot like the hoodoos, tent rocks, and "fairy chimneys" at Cappadocia in Turkey. Notice the softer, pinkish part of the section near the base of the the central and most fully exposed hoodoo, the white caprocks or "tents" all across the hill, and the darker-colored outcrops near the top of the hill. This outcrop pattern of light-colored rock beneath darker rock is typical of many ash-flow sheets in Nevada, and that's what this most likely is: a poorly welded (bottom) to maybe moderately welded (top) ash-flow-tuff cooling unit.
From Vya, as you remember, we drove south then west onto old Highway 8A (now a county road, possibly still called 8A), and started climbing over an unnamed pass through the Hays Canyon Range. MOH and I hoped we would see some of these hoodoos up close, and sure enough, when we rounded a bend one was sticking out right next to the road!
one regional ash-flow sheet in south-central Nevada.
Let's get closer:
|Here's a fairly large, subrounded lithic fragment within the tuff.|
|Zooming in a bit, we see that the matrix of the tuff is fairly fine-grained, fairly well-sorted, and some grains look sharp and appear to be interlocking.|
|Here's another view of the rock: Rounded to sub-rounded lithic fragments and white pumice float in a fine-grained matrix.|
|I'm pointing to one of the white pumice fragments in this enlarged view.|
Standing back and looking at the overall mien of the outcrop, I'm going to have to stick with poorly welded ash-flow tuff.
this one geologic map by Egger (2010), a regional map focusing largely on the Warner Range to the west but also including part of the Hays Canyon Range. According to the map and accompanying text (both are available for download here), these hoodoos and rock formations occur in what has been called the Fortynine Tuff by Carmichael et al (2006) in an article I didn't access (paywall).
|I noticed (after the fact) a couple intriguing joints within the tuff, including two that might have veins of some sort or slickensides (the upper, center one in shadow, and one just below it and to the right, also in shadow).|
A Few References:
Carmichael, I.S.E., Lange, R.A., Hall, C.M. and Renne, P.R., 2006. Faulted and tilted Pliocene olivine-tholeiite lavas near Alturas, NE California, and their bearing on the uplift of the Warner Range [abs link]: Geological Society of America Bulletin, v. 118, no. 9-10, p. 1196-1211.
Egger, A.E., 2010, Geological history and structural evolution of the Warner Range and Surprise Valley, northwestern margin of the Basin and Range Province [Ph.D. thesis]: Stanford University, 180 p. Plate1.
Egger, A.E., and Miller, E.L., 2011, Evolution of the northwestern margin of the Basin and Range: The geology and extensional history of the Warner Range and environs, northeastern California: Geosphere, v. 7, no. 3, p. 756-773.