Surprise Valley, CA lava flow (0819)

I guess the surprise is that single tree standing there all by itself.

You might be teasing there.... in any case, my focus was on the size of the lava flow and using the tree to help illustrate its size.

Lone poplars like that are often a sign there used to be a building there.

Here's my off-the-cuff interpretation: the break in slope along which the highway is nearly running reflects the trace (surface expression) of a high-angle fault. Relative movement is down to the right, up to the left, and the slope, altho modified by erosion, is probably still pretty close to the plane along which the faulted units moved. So it's dipping to the right maybe 35 degree or so. It looks to me like there are a number of stacked lava flows, not just one, and they overlie light-colored sedimentary units, altho they could be tuffs. (I'd need a closer look!) So I'd predict that this same volcanics-atop-light-sediments stack is also out there in the valley, now buried by the younger lake sediments. If the correctness of this interpretation were of economic importance you could check by drilling! This also indicates this slope represents a cross section laid open by the faulting--iow, the volcanic units have been truncated by the fault here.

As to why the volcanics look so flat--they probably were deposited on a reasonably flat surface that hasn't been tilted subsequently. Since they're pretty durable rocks, if there were originally more units (sediments, say) deposited atop them, those units could have eroded away more easily to leave the hard lava units sticking up as a ridge. The sediments under the lava are protected from erosion (at least fast erosion) by the lava cap. Iow, this ridge looks to me to be a product both of faulting and differential erosion.

OK, sorry for the long-windedness--