Day two of our trip found us doing much of the same thing as yesterday: mapping fluvial and volcanoclastic deposits. This time we learned how to measure strike and dip of the observed bedding. Here’s an aerial view of our work area:
This out crop is where we spent most of our time taking measurements. What you’re seeing is some severely tilted beds of volcanoclastic material. The dip is nearly 60 degrees at the top and becomes less angled as the bed continues dipping.
A slightly closer shot of the same area:
Here’s a close-up of the clasts present in some of the bedding:
The source of the tilting is probably some plutonic intrusion. I’m inferring this based on the presence of a sill that sits just to the left of the first set of tilted bedding.
Here’s the view at the top of the basaltic rimmed plateau. Not sure if my camera got it, but you can see Mt. Hood in the background.
Day one of my strat trip found us mapping fluvial and volcanoclastic deposits in the Cove Palisades State Park. It was nearly four hours of hiking up the road, examining the road cut, and taking measurements. What did we find? Lots of fluvial deposits such as rounded cobbles and sand stone towards the lake and volcanic teffra towards the top. Here’s a few pictures to show the sequence. I included scale where it was safe to do so. I can’t get into too much detail because I’m posting this from my phone.
Our work area seen from the top
Layer of cross-bedded sandstone on the bottom with rounded cobble on the top. All indicative of fluvial deposition.
Welded ash with pumice
An example of beautiful cross-bedding in sandstone
The meeting of fire and water. The rounded cobbles at the bottom were deposited in a fluvial environment. The thick layer in the middle is from an ash flow, while the layer directly above it is ash fall. The later directly above that is more rounded cobble.
Another example of beautiful cross-bedded sandstone and gravel.
And to end it all, nice columnar basalts.
Lockwood over at the Interzone has recently noticed that there’s a columnar basalt theme going on in the geoblogosphere. So, to keep the ball rolling I thought I’d throw in one from central Oregon. This one is from outside the town of Kimberly, OR. I took it while on a field studies trip to the John Day Formation. If I’m remembering correctly this outcrop is part of the Picture Gorge basalt flow which is about 15 million years old.
Crude columnar basalt formation- Picture Gorge Flow