Saturday, March 1, 2008

Picture of the Day - A Great Outcrop

Death Valley and environs is an unendingly fascinating collection of naked rock exposures. The next post or two concentrates on a particularly instructive roadside classroom east of the park near the Nevada border. It is rather famous amongst Death Valley travelers, and has been featured in a few textbooks as well. With a caption that as often as not is incorrect!

Clearly a fault exposure....what kind of fault is it? It is a problem my first year students get to deal with on the second day of their field trip to Death Valley. If you know this outcrop well, hold back a few hours and let others give it a shot.

4 comments:

CJR said...

If I'm reading the perspective right, the outcrop surface is quite a shallow incline rather than a vertical road cut? That would make it a strike-slip fault.

Ron Schott said...

I'd say it's clearly a dip-slip fault. My guess is that many textbooks identify this as an example of a reverse fault, based on the apparent offset of the rusty orange-yellow beds. If they got it wrong, as you imply, I'd have to presume that this is actually a normal fault and those particular beds are not correlative. Normal faulting certainly makes more sense given the likely age of those volcanics and the current tectonic stresses in the region. But of course, I could be wrong...

Silver Fox said...

I haven't cheated and read ahead, yet. I've been to this road cut, so long ago that I don't remember anything but the rock types, not the fault.

In the photo, if those are the same "vitrophyres" - it looks like reverse offset. Given the location of Death Valley, however, it could be a tilted low-angle (or moderate angle?) normal fault - a process related to detachment faulting.

Now I'll read on and catch up!

Ron Schott said...

Authoritative answer?