Tuesday, April 4, 2017

From the Road: Talus-y Goodness and More of the Roan Cliffs, and a Question (at the end)

I was looking back through some photos and realized I had some of the Roan Cliffs from the spring of 2006. These first two photos are taken from an impromptu campsite MOH and I found not far from the Rulison exit on I-70, and they somewhat approximate the views seen in Ron Schott's excellent gigapan of the cliffs. I'd embed the gigapan here, but Blogger seems to have some problem with either the iframe coding or the flash implied within the code (or maybe it's Chrome, and I'm being deluded as to what's possible). In either case, we're looking northwest toward the cliffs in the first photo (above), and northeast toward the cliffs in the second photo (below).
It was a very green spring, according to these photos, so the color balance doesn't match with my fall 2016 photos below, which were taken from near or at the Rulison exit. Also, my Nikon tends towards blue.
The reason I stopped for these particular photos during my semi-mega roadtrip of last fall was the talus. I found the striping caused by alternating zones of vegetated and non-vegetated slope areas to be fascinating in the way that perhaps only a geologist, geomorphologist, or photographer can. So I grabbed a few quick shots focusing largely on the talus slopes. More recently, I decided some approximated geologic contacts were in order.
In this photo (above), the cliff and talus slope below the cliff are formed on the Tertiary Green River Formation (Tg), and the colorful beds near the bottom of the photo consist of the Tertiary Wasatch Formation (Tw). The thin cyan line near the base of the cliff marks (hopefully) the top of the Mahogany ledge as extrapolated from this USGS preliminary geologic map, as deduced from this report (Fig. 9, p. 16)—which points out the top of the ledge in a cliff to the west—and as mapped from Ron's gigapan of the cliffs. A few other reports were helpful for exploring the general geology and reading some background info about the ledge and zone—it's called the Mahogany zone when intercepted in drill holes.
In this set of two photos, I've zoomed in on the striped talus section that was on the far right of the previous two photos. The vertical striping of the talus contrasts nicely with the horizontal layering of the Wasatch beds, don't you think? I've labeled the photos below. This time, a tiny bit of the Tertiary Uinta Formation (Tu) is barely visible at the top right. The stratigraphic contact between the Tg and Tw is crudely outlined in faded cyan: It crops out behind the foreground slope where we can't see it.

This set of two photos is not that different from the previous set, but here (below) I've sketched in the Mahogany ledge (as approximately extrapolated), and I've broadly labeled the geologic formations without drawing in the contacts. The circle is where an old mine, the Rulison Oil Shale Mine is shown on the topo map of the area  (USGS TNM 2.0 Viewer link). I can't see it there in the photo—though maybe it's just not apparent—but there is a tiny black area that *might* be an adit just beneath the arrow.
The cliffs in these 2016 photos lie northwest of the Rulison exit and occur between the first two 2006 photos.
In this last set of two photos, we're looking northeast from the Rulison exit, zooming in on cliffs that approximate what we can see in the second of the two 2006 photos. I once again focused in on striped talus, but then I really zoomed in on some switchbacked roads that I thought might be drill roads. It turns out that the switchbacks climb up to some underground workings into the Mahogany ledge, which I've marked approximately with a thin cyan line (below, with thicker lines marking formational contacts; Tu = Uinta Formation; Tg = Green River Formation). The line is taken directly from the previously linked-to preliminary geologic map of the Anvil Points Quadrangle (O'Sullivan, 1986). The map can be viewed directly in Google Earth, an option I always appreciate.

The underground workings here consist of several adits comprising the Anvil Points Oil Shale Mines. The mine was active intermittently from 1925 to 1982 (the last link includes some undated photos), with some clean-up operations running from 2008 to 2013.
How do you spell Talus-y? I see 3 options: talus-y, talusey, and talusy. I went with the first option in the title but prefer the last. Yes, I know it's not a *real* word.


jusTodd said...

its a real word now. you typed it. ;)

Silver Fox said...

Haha :-)

Dan McShane said...

I vote for #3.

Silver Fox said...

I'm not getting too many votes so far, so the winner is talusy.