Geo 365: Nov. 26, Day 330: Unreachable Conglomerate

There's a very nice cracked pebble conglomerate exposed in this cliff face. It's an outcrop I had visited only once before, on a field trip in the mid 80's. On that trip, we had to clamber over driftwood to get across Brush Creek, but there was a decent beach we could walk up to look at the exposure. On this trip in May, winter storms had removed most of the driftwood, and the creek, still high with spring runoff, had meandered up against the cliff. In addition, it was too swollen to wade without removing shoes and hiking up our pants to our knees. As I've mentioned a number of times, the coast portion of our trip was nasty cold, and removing articles of clothing was not a practical option. So, much to my disappointment, we couldn't really get a look at it.

In my poking around the innernetz, I came across a Master's thesis on the geology of the area from 1960 (8.9 Mb, link to archive, not direct to PDF), which shows a significant fault roughly along Brush Creek (See fig. 4, pages 14 and 15 as numbered by the PDF, rather than as paginated in the original thesis). Since I hadn't really looked at the geology that carefully on either visit, I hadn't dinked that out for myself, but in retrospect, it's pretty obvious. As we'll see in days to come, there's quite difference in the rocks on either side, and a fault is an obvious explanation for that discrepancy. As a side note, I haven't read that document in any detail, but I'd take much of the interpretations carefully. With utterly no disrespect to the author, our understanding of pretty much all of Oregon was overturned- at least greatly modified- by the plate tectonics revolution of the 60's and 70's, with much of our "flake tectonic" understanding developed during the 80's. On the other hand, most of what I have read is mostly descriptive, and is very useful. What the rocks are doesn't change (though nomenclature can change their names). It's our interpretation of them than can change dramatically.

Also, the picture I'd thought of using today was one I'd already posted, at the end of a "teaser" post during the trip (direct link to photo). I'd expected to expand on that description, but after reviewing it, I decided there wasn't really much more to say. It's still a cool rock, though.

Photo unmodified. May 7, 2013. FlashEarth location.