Monday, January 20, 2014

A Bit More about Toulon Peak

It was a hazy winter day when I pulled off I-80 at the Toulon exit, thinking that I'd find a dirt road and check out some tufa mounds and domes along the same Lahontan shoreline where this mound occurs, but about nine miles away (shoreline miles).
If you pull off at Toulon, take the Ragged Top dirt road, which heads NW then WNW toward a low pass in the Trinity Range south of Toulon Peak. Don't, in this case, head toward Toulon, the moth-eaten old mill seen just right of the sign.
I drove the road up the alluvial fan, passing by the distant tufa mounds, not finding a road that would take me directly to them. I finally turned onto a side road about 1.5 miles beyond the I-80 underpass, but realized I was quite a ways past the shoreline of interest.

I decided to, once again, test blog a photo from my new mobile device, using the Blogger App for Android, which is getting quite variable reviews. A major problem for me is that the app has no option to control placement of the photo in the post or the size of the photo (without going to the web version of my Blogger Dashboard, which works quite well).
I shot this photo with my phone, looking west. Toulon Peak is the high peak.
I shot this photo with my camera. At this point, neither photo has been modified by adding contrast or color, nor has either been sharpened.
My biggest disappointment was something I noticed over the holidays while in Alaska: the Blogger App will not give very many choices for location. In Alaska, I was given the choice of a very precise (and accurate) location that would have pinpointed my mom's house within a mile or less (more precision than she would have liked), or some nearby locations such as a local park and several commercial establishments. I wanted to just use "Anchorage, AK" as the location, but the app doesn't allow entering anything not on its commercially oriented list.

Near Toulon, within two miles of I-80, the Blogger App could only give me the location of "The Americas", not nearly close enough for my purposes. I was within range of the Verizon 3G network, had no problem uploading the post and publishing it, but the app didn't offer me a way of indicating I was anywhere within the states, within Nevada, or close to Lovelock, let alone near Toulon. I'm pretty sure that the #NSA would have been able to locate me, and no doubt Google Maps knew where I was, although I didn't think to check it out -- I was in a bit of a hurry, trying to outrun the setting sun.
Here's a version of the phone photo, cropped to more closely match the camera shot, and with added contrast and slightly adjusted color.
And here's my enhanced camera shot.
The hills in the foreground, all the way back to the white hill capped by orange-brown and dark brown rock, are composed of relatively young volcanic rocks, which are generally listed on state maps as being within the 6 to 17 Ma range. The white section of rocks, called Tts on the Pershing County map, probably correlates with the Esmeralda Formation to the south and the Elko Formation way to the northeast. These are the early to more recent basin-filling sediments, often tuffaceous, sometimes diatomaceous, that began filling basins just after the start of basin-and-range faulting and basin opening. These are typically capped by young ash-flow tuffs, young andesites or basaltic andesites, and basalts. It's unclear to me what the capping dark brown and orange-brown rock is from this distance.

Toulon Peak appears to be underlain mostly by young volcanic rocks, also shown as being within the 6 to 17 Ma range, although Jurassic-Triassic sediments and metasediments of the Auld Lang Syne Group and some Cretaceous granodiorite are shown on the county and state geologic maps, mostly south (left) of Toulon Peak.
A Google Earth view of the area, as seen from the same location I stood at when taking my photos. The white section shows better in this view.
Here, I've cropped the Google Earth view to more closely match my photos. We can see more detail in this view, because Google Earth isn't plagued by inversion haze and smog.
The geology is still somewhat obscure, but it is a little clearer (especially upon examination of Google Earth) that the units in the foreground are probably the same as the units back into the middle ground, where a dark brown volcanic layer overlies a white unit, which overlies an orange-brown unit, which in turns overlies the lower white section. In some lighting, and on Google Earth, at least two dark bands show up -- these may be basaltic sills (similar to some down in the Gilbert mining district near Tonopah), or they may be vitrophyres within young ash-flow tuffs.
The volcanic section described above, as seen in Google Earth.
Of course, this is mostly speculation until field checked!

As it turns out, this is the location of the Ragged Top caldera, about which I could find very little online, but which I was just clued to by a commenter who mapped in the area in 1987. I'm listing a few references about the area below. What I found was that the caldera is about 12 million years old (Masterson, 1981). The same source lists a 23 Ma age date for an obsidian nodule on the west side of the range, indicating that some older volcanic rocks (in the 17 to 34 Ma range) occur in the area. Age dating may be complicated by hydrothermal alteration in the region.

It appears from the county map and Google Earth that the caldera is located mostly south of my photos, beginning just south (left) of the white rocks described above, in what is mapped as Twt (welded tuff) on the county map. The caldera, however, could be located in the younger Tr around Toulon Peak.

A Few References:
Harpel, G., 1980, Geology and tungsten mineralization of a portion of the Ragged Top Mining District, Pershing County, Nevada [citation only]: University of Nevada, Reno, M.S. thesis.

Johnson, M.G., 1977, Geology and mineral deposits of Pershing County, Nevada [front pages only]: NBMG Bull. 89.

Masterson, W.D., IV, 1981, Epithermal gold mineralization in the Velvet District, Pershing County, Nevada [entire pdf]: University of Texas at Austin, M.A. thesis.

Thole, J.T., 1991, Ragged Top Caldera; geology and geochemistry of a Miocene volcanic center, Pershing County, Nevada [citation only]: Washington State University, M.S. thesis.


Anonymous said...

I actually did a measured section of that particular hill back in '87. Black bands are indeed basal vitrophyre, The cap rock is densely welded ash flow tuff. Lowest light colored rock are tuffaceous sediments, with some nice petrified wood in places. Compound cooling unit in terminology of Smith

Silver Fox said...

Wow! So cool that you were there and that one of my ideas was right -- it looks like a really neat place to walk over to. Sometime when I have the time...