Saturday, April 21, 2012

March 2012 Coastal GeoGalavant, Part II

Day 2, Stop 7a: Sunset Bay State Park- Our last, and most involved, stop of the day, there's a slew of things to see here. On top of that, the park now "closes," whatever that means, at 6 PM, at least during the cold months... I don't know how they could justify or enforce that during the evenings during the summer, when the sunsets are about 9:00 PM, and twilight lasts until nearly 10. At any rate, we decided to head back to the car sooner that we'd have liked, to make sure we didn't get locked into the parking lot. Only to discover the exit has a gate, but the entrance doesn't. WTF!?
 Looking ~SW across Big Creek, at weathered spruce stumps, supposedly killed by earthquake-associated subsidence about 1000 years ago. I say supposedly, because this trip was first I heard this, and the source, a pamphlet Dana picked up at Shore Acres, did not look very well researched or knowledgeable to me.
 Dana on the same stump for scale. From here, we walked up stream a bit, maybe a hundred yards to a footbridge, then back along south shore.
I'm on a stump! Looking across bay to north shore. There's less to see on the south shore than along the north, but these stumps are a kick, and worth the effort on their own. However, there are some other noteworthy features. For example, see Dana's post on strike and dip... this site is a nice clear example of a concept that we tend to forget is abstract and confusing for beginners. One of the major features discussed in an old DOGAMI field overview (3.2 MB PDF) is the "drag folding" associated with a strike-slip fault running through the bay. The drag folding has confused me for as long as I've visited the area. This trip, I figured out why.
 Turning and looking the opposite direction from the spot where I took the second photo in Dana's strike and dip post, the "drag folding" is apparent, with the sense of offset to the left. In other words, if this is drag folding, the opposite side of the hidden fault should have moved left with respect to our perspective from this side. But wait...
This is not very far away, probably less than 50 yards farther to the NW along the wave-cut platform. Bafflingly, here, the sense of offset is to the right. I noticed there was a kind of chaotic area between these two spots, and out closer to the water's edge, but I hadn't quite grasped the conundrum until I was going back through the photos that evening, so I didn't think to get any shots of that area. The problem, if it isn't obvious, is that if this is drag folding, the fault was moving in both left-lateral and right lateral senses, and that don't work.  I think rather than saying there's something weird going on here, I'll just say there's something going on here that I don't understand, and won't be able to make any sense of, at least until I get back. It may or may not have a simple solution, but I can't tell from Corvallis.
Finally, we mustn't ignore modern features. Above are some nice examples of snubbed ripples, asymmetric current ripples whose crests were planed off flat, or snubbed, by last bit of sheet wash as the previous high tide receded.

Blooger has changed their interfaces yet again, and I'm exasperated, but slowly figuring out how to function in this new environment. So I think I'll just drop this for now and come back to the north shore portion of Sunset Bay later.

1 comment:

Phil said...

Awwe, you missed the little cave way out on the South side!

There is a bigger one at the very South end of Bastendorf beach. It actually goes in quite a ways, about twenty five feet.

The North side of Sunset?
When I was a little kid, we used to climb up the clay cliffs with the natural slides and slide down them for hours.

I used to party real hard at Sunset in the early eighties.

Lot's of good times.

There used to be one lone tree at the very top of the North side as far west as the trail would go, it was a beautiful, lonesome tree and some jerk killed it.

It was a shame.
When the sun would set in the evening and the sky would turn pink and orange, that tree was picture post card beautiful.

I did not know until about ten years ago that there was actually an amusement park at Sunset in the thirties.

Glad you had a good time.