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A Rambling Writer Guest Post: Geologist Thor Talks More Rocks

By popular demand, Thor explains the colorful variety of stones found in our Pacific Northwest.

Sara asked me to contribute a blog on our recent obsession with rock tumbling.  First a little prologue about the local geologic context, and why we have such a variety of stones here in the Pacific Northwest:

A few hundred million years ago, there was no Washington, Oregon, or California.  The ocean lapped up somewhere in what is now Idaho, Nevada, etc.  There has been a subduction zone on the west coast of North America, which means that Pacific Ocean crust has been sliding under the North American continent all that time.  The sliding is not smooth, however; the rocks get stressed and bend and then break in earthquakes, gradually lifting the crust and producing mountains.  The descending crust melts when it gets deep enough, and the rising hot magma produces volcanoes and also cooks the surrounding rocks.  In addition, the Pacific Ocean crust has lots of islands and seamounts.  These bumps get scraped off when they hit the continent and gradually grow the continent westward in a process known as continental accretion.  All of this squeezing and heating changes rocks in a process called metamorphism.  Metamorphism can turn a rather blah sedimentary rock (rocks formed from lake, ocean, or desert sediments) into a beautiful stone with garnets and mica.  So, we have distant rocks coming from the west and being metamorphosed, magma and volcanoes rising, and the whole mess being squeezed and uplifted into mountains that form a rich source of varied rock types.  Then we had glaciers cover the whole state to a depth of a mile or more.  If you flew over Washington 15,000 years ago, all you would see would be ice and the tips of the Cascade Mountains peeking out.  The glaciers carved out chunks of rock and carried them downslope toward the ocean.  We’ve had numerous glacial advances and retreats, so these rocks were dumped pretty much all over, and their source may have been hundreds of miles away.  This means when you browse through the pebbles on the beach you are looking at volcanic rocks, granites, sedimentary rocks (sandstone, shale, limestone), and metamorphic rocks that may have originally come from hundreds of miles away.  That’s why I love polishing beach rocks; each one tells a story.

I started collecting fossils when I was a kid.  Around age 10, I would load some tools and a lunch into an old army pack my father gave me and hike through the woods to a local fossil locality.  That is what kids did then; leave the house to wander around and get in trouble.  But you better be home for dinner!  I pursued this passion into high school and college, eventually getting a degree in geology and becoming a college professor teaching paleontology and geology. Sara insisted I add this photo of my last on-campus teaching day after 40 years, holding a cast of an extinct American lion skull:

Fossils were my specialty, but I always liked rocks.  I would sit on the beach and look for pretty pebbles and try to classify them as igneous (once molten, like lava or granite), metamorphic (changed by heat and pressure), or sedimentary (sediment laid down by wind or water).

Sara and I sold our house in May and have been living in a rental while we build our dream house.  All my tools and crafty things are in storage (the permitting process was MUCH longer than anyone anticipated), and I was bored, so on a whim I got a rock tumbler.  The tumbler came with a pack of stones to polish: agates, tiger’s eye, lapis, etc.  These polished up very nicely and are quite pretty, but they are also fairly common, i.e. they are the rocks that everyone polishes.  They all look pretty much the same.  So on a whim I threw in some beach pebbles.  Oh My God, what a revelation that was!  Those dusty, fairly nondescript stones turned into beautiful pearls, each with a different story.  No two quite alike.

I’m posting my complete blog entries on my own author website at, where you can finish this episode and enjoy all the accompanying photos. You can also view the complete Italy series there, as well as many other Rambles. Please continue reading by clicking on the link below, then you can return here (use “go back” arrow above) to comment, ask questions, or join a conversation. We love your responses!


You will find The Rambling Writer’s blog posts here every Saturday. Sara’s latest novel from Book View Café is Pause, a First Place winner of the Chanticleer Somerset Award and an International Pulpwood Queens Book Club selection. “A must-read novel about friendship, love, and killer hot flashes.” (Mindy Klasky).  Sign up for her quarterly email newsletter at



2 thoughts on “A Rambling Writer Guest Post: Geologist Thor Talks More Rocks”

  1. My father and I used to do that when we summered on the east end of Long Island. The beach pebbles were amazing. My mum however did not appreciate the occasional one that got left in a pocket and got into the clothes washer! I still have a collection of mason jars of our polished hoard.

    1. Surprising how many people have fond memories (or for your mother, not so fond) of rock polishing. When I was a girl, my grandpa had a gold mining claim and cabin in the wilderness mountains, and his buddy Knut Knutsen would give us polished pebbles from his hoard. (Alas, no gold.)

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