November 11, 2009

Oyster Dome…almost

Filed under: Geology, Hiking, North Cascades — geezerwriter @ 4:55 pm

Lummi & Orcas Islands

Does a forecast of high winds and 100% chance of rain keep us from hiking? Well, some of us, maybe. But there were eleven brave fools souls who came out for the hike to Oyster Dome and I don’t think anyone regretted doing so. Everyone was in full deluge regalia and it seemed as if it were about to rain at every moment; but it only managed a few drops now and again.


Oyster Creek

But the winds came as promised.

The weather around here is generally mild in almost every way – temperatures are moderate all year (80F is considered a “hot” day in summer and daytime temps are seldom below freezing); rain is frequent in the “winter” but is usually a gentle drizzle; and when it snows at all, it is usually less than an inch at a time (and that usually melts the same day).

But the winds! Every now and then the wind just rears up and blows and blows for days at a time. It blows down trees and rearranges your patio furniture and generally  just gets on your nerves, since you just can’t get away from it unless you have a soundproof room where you can hide out

The big fir, cedar and hemlock trees have very shallow root systems, and a very common sight in the woods is a tree trunk lying on the ground and an enormous flat disc of roots and dirt sticking straight up in the air – most people talk about trees having “root balls” but these are “root plates”! So even though we were sheltered by the forest from the direct blast of the wind most of the time on the hike, we had to hope that there would be no sudden visitors dropping onto the trail.

Oyster Cliff

Early on, we decided to skip the short hike from the main trail out to Oyster Dome. We usually get blown off that exposed rock dome and back into the woods even on a moderately windy day, so we went instead on the even shorter trail toward the so-called “Bat Caves”, thinking it might be a bit scenic but not so exposed as the dome above. No one in the group had ever spent much time there and the trail gets a bit sketchy and ill-defined, so we didn’t know whether the pile of enormous boulders that we came to was our intended destination or not. There were big cavities between and under the boulders that might have passed for caves, but Carlsbad Caverns it wasn’t.

But it was a pretty spot, with the sheer cliff rising up to Oyster Dome. I hadn’t done any geology homework before the hike, thinking that everything from Fairhaven down to Blanchard was plain the old Chuckanut Formation, mostly sandstone with some shales and such mixed in. But on the way up the trail there was a whole lot of dark, nondescript rocks along the trail that surely didn’t look like Chuckanut Sandstone, but might have been a shale. There was too much of it and it was too angular to be a glacial deposit (glacier-borne rocks are normally a mixture of types and usually polished into a more or less rounded shape). But up at the “caves” I saw what looked like quartz inclusions in some of the rocks (not unlike the stuff we saw on Anderson Mountain the week before) and that didn’t fit very well with what I’ve seen of the Chuckanut Formation elsewhere.

So when I got home I pulled up the WA state geology department online geologic map, and sure enough the valley of Oyster Creek is the dividing line between the Chuckanut Formation to the northwest and, on the Blanchard Mountain side, a patchwork of the various kinds of (mainly) metamorphic rocks that are typical up in the North Cascades (including the ever popular Darrington Phyllite, again). As far I could tell, given the lack of reference detail on the geologic map, the area around the “caves” is listed contradictorily both as “gabbro” and as “Shuksan Greenschist”. It certainly wasn’t the latter, which I know pretty well, and I thought gabbro was blacker (although I’ve never seen it up close) so more research is needed. Dangnabbit! Now I’ll have to go do that hike again! Rats!

The wind really fired up on our way down Max’s Shortcut on the windward side of the mountain, and the trees were swaying and dancing above us. When we got to the Samish Overlook , which is a popular jumping off point (literally) for parasailors who fly down onto the Samish Flats, it wasn’t windy enough to take us airborne, but it looked like Cindy was ready to try.


Or is that Thor about to send thunderbolts down on Samish Flats?


  1. Wonderful photos! Great commentary, Al. I’ll be there tomorrow, since I was waylaid by a doctor’s appointment right in the middle of the morning. Otherwise I would have been there, and I hoped that maybe you had changed tomorrow’s hike with last weeks, but I’ll happily do Stewart again! The weather looks pretty darn good.

    Comment by DJan — November 11, 2009 @ 6:40 pm

  2. Hi there! I have a blog about NW geology fieldtrips, and will shortly be writing up the geology of the hike to Oyster Dome. You re correct, it isn’t Chuckanut, but it really is related to the Shuksan rocks. I’ll get that story on the blog in the next week or so.
    Enjoyed reading of your hikes.
    I live in Bellingham.
    also: for the latest on Mount Baker geology

    Comment by Dave Tucker — January 2, 2010 @ 1:01 pm

    • Hi, Dave. We met at the Mount Baker club meeting where you spoke last fall. In the meantime I found an article on the geology of the Bat Caves in “Hiking Washington’s Geology” by Scott Babcock and Bob Carson. It also points out several spots along the trail where there are interesting outcroppings of one thing or another. I look froward to doing the hike again with this new knowledge and will be subscribing to your blog.

      Comment by aheezen — January 2, 2010 @ 1:51 pm

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