Here's a nice shot of Cooper standing on the ~5 meters of coarse fluvial gravel that sits on the Bogus Rim lava approximately 1000' feet above the Owyhee River. The gravel is composed entirely of basalt (~90%) and rhyolite (~10%) clasts. It is only well exposed at spotty locations along the rim. The Bogus Rim lava comprises only the few meters at the top of the exposed section. The remainder is the undivided Bogus lavas which filled deep paleotopography in this area.
So, could this gravel be filling in behind a Greeley lava cap? Or what are your thoughts about its origin?
ReplyDeleteBy the way, the gravels that Evans maps extend quite a ways upstream. For example, there is Qal mapped on top of the canyon rim in vicinity of -117.306, 42.701.
The relatively limited lithology represented in these gravels and their calibre suggested to me at the time that they were a record of the first incision into the Bogus Rim flow. It seems that in other places the gravel assemblage related to damming (possibly including the 'dreaded rim gravels') are finer-grained and polymictic. That being said, we need to look for a site where we can relate the rim gravels to the Bogus Rim gravels.
ReplyDeleteI am becoming more and more intrigued about Jim's suggestion that the drgs may be related to damming by Bogus lava.
There appear to be some interesting paleochannels in the area of the coords you provided.