Geo 730: Jan. 15, Day 380: Grassy Flat

"Grassy Flat," at this point, is basically mis-named; it has been cleared and driven on to the point that it's mostly bare ground, dirt and rock. But it is another good example of a fluvial terrace, much like the area upon which Gasquet was built. We're looking across the Smith River here, hidden behind the brush, to a large hillside of unconsolidated debris. I can't say with any certainty what its origin is, but I think we can narrow down potential sources. Some that spring to mind are an older, higher terrace, glacial moraine or outwash, an older, filled and abandoned river channel (these are quite apparent in other locations along this drainage, which is why this possibility occurs to me), or deposits from debris flows- essentially, an alluvial fan.

Looking carefully, the sorting of the clasts is poor to the point of being non-existent. I see very little evidence of bedding, with the exception of an orangy band that starts just below the tree line near the middle, and dips off to the right. The lack of sorting and bedding seems to weigh against a fluvial origin, so I'll withdraw the terrace and channel options, as well as the outwash conjecture. We're much too low in elevation for glaciers to have reached this spot, so I don't think a moraine is a viable guess, either. (Backing out in the FlashEarth view supports this: the drainages are clearly "V-shaped.") That leaves debris flow deposits/alluvial fan as the remaining option. As I said, I can't be certain, but given the situation and topography, that seems to be the best conjecture: an alluvial fan that's been carved out by subsequent meandering and erosion by the Smith River.

Photo unmodified. May 8, 2013. FlashEarth Location. Indexed