Sunday, June 26, 2016

Cape Arago Oregon

Down on the Southern (well, mid-southern) coast of Oregon is the little community of Coos Bay. This bay is formed where some small rivers and a bunch of built up sand dunes have created a little bay.

Sticking out into the Pacific just west of Coos Bay is Cape Arago. This is a beautiful geographic feature and a very nice state park. I spent an afternoon walking around and taking pictures of the rocks and animals and trying to figure some things out. I was lucky enough to spend part of the time with a marine biologist, so I even have some critter stuff here.

First, the rocks. You know how you can find sedimentary rocks and layers if you go to the ocean or perhaps the mountains (or the Grand Canyon)? You can see the horizontal stripes in the rocks and know each of these stripes represents some geological era. You can sort of count backward in time as you go lower and lower into the ravine? Well, Cape Arago is nothing like that.

At Cape Arago, all of those horizontal lines run vertical.

Here is the story as far as I can piece it together. I read a few papers by a geologist but their science words are different from my science words and I may have gotten some of this wrong. Forgive me. You can take a shot at the paper yourself.


Millions of years ago, the Northwest coast was much flatter and more gradual that it is today. The coastal range didn't exist and a gradual flat silty, sandy, coast stretched much farther inland to the foot of the current day cascades. This was a shallow water ocean and according to what what going on in the word, different strata would form on the bottom and get compressed into rock. Sand would form for a few feet and turn into yellow sandstone. Silt would form a few feet and turn into grey siltstone. A little volcano action would happen and some lava would run through and get deposited. A particularly heavy biological era would occur and the resultant organics would get pressed into coal. And so these layers continued to build up. A few miles thick of lots and lots of different layers. Now we have some drifting plate action occurring. The middle of this area sinks down a bit (forming the south slough) and the land on either side gets pressed up until the horizontal layers become vertical layers sticking up into the ocean. Now we have these big cliffs sticking up and wave action comes into play on them. Over the centuries, the soft materials (like sandstone and coal) get worn away while the harder materials (like siltstone) stay in place and form the cliffs and islands.

There are also various small faults in the area that create breaks in the hard layers. In one place, such a break lets the sea in through a small gap. The waves crash in and wear away the soft layer on the other side of the gap to form the beautiful round sunset bay. Right beside sunset bay, the obstinately hard rock sticks out into the ocean forming Lighthouse Island.

Lighthouse beach is the strip of sand just North East of Lighthouse Island. The day that I was visiting, unusual wave action had stripped the beach of its usual layer of sand and I had a chance to wander through a lot of normally covered striated rock and take some pictures.  I walked around trying to figure out what runs of rock went where. You could see how it would travel up the beach and then up the cliffs and back into the headland. Fascinating.

And then there were the sea creatures.

A micro Mass Stranding

On this particular sunny and wonderful spring day, the waterline was covered with a flotilla of swimmers called Velella, or By the Wind Sailors. These little guys are a deep blue in color and look like an upside down limpid with a little translucent sail on top. They are actually a colony of Velalla all living tougher on the same little raft. Each colony is either all male or all female. Which seems a little crazy to me. They move through the water by the thrust of the wind on their sail and they have little tentacles that drag beneath them to catch prey. Though they aren't very dangerous to humans, you can end up itching if you handle them and then touch sensitive skin (like your face). Because of their reliance on the wind for locomotion, large groups of them frequently end up beached on west coast beaches.  My biologist friend says there are really two types of these guys, left hand sailers and right handed sailers. The handed of the sail determine which direction they tend to float, so only one hand ends up on the beaches in any given event.  Cool.

On one rock that is just about always underwater (we were at a very negative low tide) we found a kind of sea anemone that is also a colony creature. These guys breed asexually and spread all over the rock. In some places you can see lines in the arrangement that is indicative of a different colony of the same species spreading against the other colony.

The lines define the different colonies

Underneath that rock were a bunch of large Anemone. They and their small colony cousins were all closed up for the time being. They were waiting for the ocean to come back to them.

The other fascinating thing were the shells that had bored into the rock in many places. These animals have a very rough back end which they run against the rock as they grow. Back and forth, back and forth and they cut a very smooth round hole for them to live in which they enlarge as they grow.

Old rock with no critters left alive

Before leaving the area, my partner and I and our sister took a little walk around the local state camp ground. We are marking the sites that we like for some tent camping later in the summer. We are going to come back here for a family vacation and to chill for a while. One thing you can usually do on the Oregon Coast is chill. I am hoping that with my new found semi-knowledge about the rock formations I can try to get some better pictures that show the unique geography of this beautiful coastal area.

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