Monday, March 18, 2013

Geo 365: March 18, Day 77: Pluvial Delta?

Toward the west end of the Fort Rock basin, there's this odd, flat-topped, steep-sided, plateau-looking landform. It's a feature I'd been by many times before I even really noticed it, and I recall being a little puzzled when I did. It's off the road far enough that it's not really practical to get closer to look carefully- I don't doubt there's dirt roads that could get one closer, but there's too much else to see in the area to spend the time. But this is getting close to where Fort Rock Road intersects Route 31. Turning north from that intersection, 31 quickly heads up a large gorge. There's little water visible, but it makes sense that, at times, it carries substantial flow. This would have been even more true during the Pleistocene, when the basin we're in for this view was filled with water. The flat top of that feature appears to be roughly congruent with the high water stand in Fort Rock Valley, so my suspicion is that it represents a delta that developed into this pluvial lake during that time. Another possibility is that it's a fault scarp, but doesn't look right to me for that. For one thing, it's not as linear as I would expect; for another, the top surface looks too horizontal.

This is a situation where getting up close and personal would put an end to a lot of questions.

The FlashEarth view (which is approximate- as you can probably tell, this was taken on the fly) I've chosen for this shot is backed out more than normal, so you can see both the feature in question and what clearly is a fault scarp to the south. In addition, Fort Rock is in the upper right middle, and Hole-In-The-Ground, our next destination, is on the top edge to the left. Photo unmodified. August 20, 2011.

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