Tuesday, November 19, 2013

Curved Rock Piles on the Olympic Peninsula North Coast

West of Twin Rivers on the Olympic Peninsula's north shore are a series of curved land forms extending out from the shore within the tidal zone.   

North shore of Olympic Peninsula west of Twin Rivers
The road is State Highway 112

Last week I had a chance to explore this coastal reach. I had a nice break in the weather to do it and just enough afternoon light and out going tide to get a reasonable look at this lonely stretch of coast. I should add a few notes here regarding the walk on this shore. It is not frequently visited by humans and is very treacherous walking - essentially long stretches of the equivalent of horizontal talus with a variety of slippery features from sea weed to mud covering the rocks.

The curved land forms consist primarily of boulders on a bedrock cut platform shoreline. The piles of boulders form the curved forms and the curves come in various sizes. The larger and more continuous, the more consistent the curve with smaller more chaotic piles of rocks being common as well including within the more prominent curved rock forms. It is perhaps easier to see the features in aerial views, but they can be fairly easy to discern on the ground (tide flat); however, the wide scale does not lend the features to being easily captured in pictures.

The rock piles form protected pools on the wave cut platform shore

Veneer of boulders and cobbles over bedrock platform

Large pool rimmed by curve of boulders
Pillar Point is in the far distance

Curving line of boulders

Curving line of boulders

The boulders in the curved lines are different than the bedrock on the platform and at the shoreline bluff. The boulders are harder sandstone and siltstone and occasional glacial erratics while most of the platform and bluff is claystone.

Lower bluff with tilted claystone

Weak bedrock claystone

Platform of muddy breccia landslide plain

This entire reach of coast is lined with very unstable deep-seated landslides associated with the very weak claystones. The source of the curved piles of rocks is the result of large landslides that have slid out onto and across the wave cut platform transporting harder more resistant rocks to the outer edge of the slide area. After the slides take place, the wave action erodes away the soft broken landslide debris leavng behind a lag of harder boulders around the perimeter of the slide area. At least that is how I am interpreting the features of curved piles of rocks. I have a chance to better test this idea at another site, but it will have to wait for another trip out there.

These rocks are Oligocene marine and non marine rocks and are fossil bearing.

Some clam fossils

There was something of great interest to the gulls in one of the pools

Back on the road pictured in the initial Google Earth image

The first time I drove this road was during a heavy rain storm at night. Even at night it was obvious this section of highway was on a landslide or a series of deep-seated landslides. It is a very slow section of road and requires frequent patching and monitoring. 


Upupaepops said...

The whole of Hwy 112 particularly nearing Neah Bay is an adventure in driving.

Like you note a patchwork of patches.

To my knowledge there are no alternatives between Neah Bay and Seiku if the road goes.

Gravel Beach said...

Dan, Thanks for the field photos. I've seen these from the air and was aware of the landslide connection, but have only seen a few shots from ground level. Some day I'll have to get out there and take a look for myself. hs

Anonymous said...

Interesting hypothesis. I have also seen these interpreted as prehistoric fish traps constructed by native people

Dan McShane said...

Upup: It is a rough twisty road. I do think there is a back way into Neah Bay via some logging roads which are very confusing and gated. It would be along haul though via the area near La Push.
HS: it was a fun walk/scramble and I want to do another reach on a future trip.
Anon: I have been looking for examples of fish traps or aquatic farming from First Nations as I have read about them in BC. Indeed, one reason I wanted to look at these was for that reason. The bigest curved fetaures have rocks that strike me as too large; however, on some of the smaller ones one would should consider the hypothesis that pools may have been anthropogenic.

Anonymous said...

Hmm-m-m. I wonder if this has anything to do with the fact that exactly where you were at was the location of Gettysburg, a logging town that operated between approx. 1890 and 1915. They built a breakwater on the west side of the little crescent bay, unloaded logs into the water where they were boomed and shipped to other ports. Just a thought...

Dan McShane said...


I was west of Gettysburg by several miles. Gettysburg itself is a great story that I only partially know.