Today is the broader look at the outcrop in yesterday's post. It doesn't stop with the faults! What the heck is going on with the left side? Please feel free to guess in the comments section, but I'm not trying to make things mysterious or difficult; if you e-mail me I will explain it all to you. I am just wanting to show some examples of the really great teaching moments and places to be had in a treasure like the eastern California desert. If you are curious, this particular roadcut is about 4 miles east of the town of Shoshone on Highway 178 (the Charles E. Brown Highway, hence the Charlie Brown Outcrop). 
I think I've been to that outcrop (and have a sample from it).
ReplyDeleteAs I understand it, the event that produced these volcanics began out your way around the San Juans around 40 Ma and spread west to California
ReplyDeleteOooh. I never took this road, though I was as close as Shoshone. I did have a friend who did some of his masters work in the area, though, and if I recall correctly he mentioned a vitrophere in a roadcut near Shoshone. Putting two and two together, that black rock sure looks like a vitrophere. Now I'm kicking myself because I'd love to take a picture of that fault. I guess that gives me another excuse to head west again!
ReplyDeleteYes, that's the same outcrop - from a grad school field trip back in 1975!
ReplyDeleteIt looks like you have a dipping ash-flow-tuff vitrophyre, which usually develop in a horizontal, planar fashion, lying on also dipping volcanic and possiby volcaniclastic units. ?
I think these volcanic rocks are fairly young, 15 m.y. or younger?
Is there an definitive answer forthcoming? Inquiring minds want to know!
ReplyDeletegeology.csupomona.edu. made this field trip in 2004 as part of their Death Valley trip. There is a description under Death Valley (pdf file) on day 2.
ReplyDeleteUndergrad First Yr. Geo Student from Las Vegas here and I stumbled Upon your blog and at good time too!
ReplyDeleteI visited it there this weekend actually and it looked like an inigmite to me.
Rhyolitous Tuff flow followed by what may be a second flow. (Obsidian Vitrophyre) could have been the beginning of flow two cooling into glass because of the temperature difference of the volcanic debris and the ground surface; above it, may be the continuity of the flow.--Spoke to a proff after this, and he never brought up the remelting idea as you did.Very interesting!! --
I identified a 3rd fault concurrent with the two normal faults shown here. (Did you notice similar breccia scarcely shown in the second fault exposed?) What an amazing road-cut this turned out to be!
The welded tuff above and below the vitrophyre can be carved with a knife ... I wonder if it was used by native Americans for making pipes or fetishes.
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