Thursday, March 10, 2011

Sheep Rock, John Day National Monument

(Screen capture of the Sheep Rock webcam from a couple minutes ago; click for full size.) @ alerted me to the webcams at the John Day National Monument a few minutes ago, and the light over there is lovely today. The lower strata, dipping somewhat to the right, are in the John Day Formation, which last I knew was interpreted as ash deposits (fluvially reworked, not ash fall) from the older Western Cascades volcanism. The Cascades are currently confined to a fairly narrow axis of active volcanism, but in earlier stages, eruptions were more widespread, frequent and voluminous. John Day fossils record a excellent record of past life and evolution; according to the Science and Nature webpage at the site, "Here, scientists have unearthed countless fossils of land plants and animals dating back 6 to 54 million years as well as evidence of the dramatic climatic changes that have occurred." For example, the webcam page linked above claims 14 genera (genera, not species) of horses alone have been found there.

The small triangular facet at the top of the peak is Columbia River Basalt, I believe of the Picture Gorge member. Picture Gorge is just a mile or so south of Sheep Rock. In the picture below (from here, again, click for full size), the view is looking north into the gorge, and I'm pretty sure that's Sheep Rock poking up in the middle background.
As you can see, even though it may look in the webcam as if the CRB is flat-lying, it is gently folded in the area, but not as much as the John Day deposits, so this represents an angular unconformity. Incidentally, all too often, when a road goes right through some spectacular geology, as this one does, there's no convenient place to get off the pavement and look at it. I'm pleased to report there is a pullout- at least one- in the gorge. Terrific and enormous columns, though I can't remember if we found the petroglyphs that gave the canyon its name.

Another thing to notice is that even though Oregon has a reputation for being wet, that's really only the western third of the state. Most of the state lies east of the Cascades, in the range's rain shadow, and is fairly dry (though there's plenty of water at higher elevations).



SkinnyDennis said...

Next time I run 395N to Idaho from CA I'll make that jog over to SR19 and check out the Gorge.
As usual it's such interesting terrain in eastern OR.

Anonymous said...

I've stopped at that very same stop on the way to Bend.

The other nice spot in Grant County on the John Day river is on County road 20 that travels on the Middle fork of the John Day from Bates @ Hwy7 to Hwy395 near Long Creek.

Eastern Oregon is a great place.