Dana and Intrepid Companion look at the exposure from the pullout on Doherty Grade. After the terrific views, the main feature of interest here is the platy jointing in the lava flows. These appear to parallel the flow front of the lobes, and some good examples can be seen in the left middle of the photo. I'm not sure how to interpret this feature; I have a difficult time imagining the stress field that would cause such fracturing. Most of the time, though, textural and structural features such as this tell you something, it's just in this case, I'm not sure exactly what it is I'm being told.
A comment yesterday from Skinny Dennis, regular reader and occasional commenter, leads to an assessment of economic and other minerals/resources in this area. Spoiler: fairly good with respect to bentonite and diatomite, good with respect to mammalian fossils, and pretty much no other prospects. I know of no significant geologic operations in the area, though that doesn't mean they don't exist. And with respect to vertebrate fossils, just don't. They're priceless, unique and irreplaceable... and context- the geologic setting in which they're found- is their most important message. If you find such a fossil on public land, report its location to the proper agency, and leave it alone. The vast majority of us- geologists included- do not have the expertise to do these treasures of past times the justice and documentation they deserve.
A classic Basin and Range scene, this was the view across Guano Valley from our stop on Doherty Grade. The far side of the basin appears to be a series of small scarps, as opposed to one large one, as here on the east margin. The light deposits on the valley floor are a bit of a puzzle; I have long assumed they're simply salt. They may be, but thinking more carefully about it, I think that might be "salt" in the broader chemical sense rather than the typical colloquial NaCl sense. I don't think the shrubs would be as pervasive if these white deposits were, say, halite (the mineral name for NaCl). They might be carbonates- calcite, aragonite or dolomite, for example, or sulfates, such as gypsum. On the other hand, they might be simply the lightest and finest clays, and not salt deposits of any kind. However, the strong correlation between fewer shrubs and lighter ground suggests to me that the concentrations of salt are probably higher in the light areas.
From our stop on Doherty Grade (aka, Doherty Slide), looking north into Guano Valley. As I commented yesterday, from a passenger's perspective, the views are better going uphill. But you should stop, get out, and look around. Glorious!
I mentioned this area before in the Geo 365 series, here and here, but here's a different view, to the south, showing Guano Valley and the scarp to its east. I've only come down this way a couple times- normally, I've continued east to Denio Junction, then up north through the Alvord Desert, heading over to the west side of the Steens near Fields, OR, or continuing up the east side (which is a spectacular drive) to Route 78. On this trip, we had already booked rooms in Lakeview, so we came back this same way. The views are better going uphill, though.
Looking to the north of Route 140, on the eastern scarp of Guano Valley, we see a pair of small alluvial fans. The rock looks like basalt from a distance, and in most cases wouldn't hesitate to identify it as such based on the photo. However, the outcrops I've looked at leave me a little confused, and I'm honestly not sure what kind of rock it is. We'll get to the main one I stop at soon...
Back on the move again, we've turned to the SSE, mostly paralleling the eastern edge of the Warner Valley. The road turns east a bit before the fault scarps in the mid distance, up a canyon, and over a pass toward Guano Valley. We were running much later than I had hoped, but said canyon also has a lot of similar tuffaceous rocks as we saw in the canyon to the west. While I've never stopped to look carefully, it looks like the exposures are even better. However, I'm sorry to say, I didn't shoot any photos there.