Thursday, October 16, 2014

Moonstone Beach and Rock Answers


So, we decided to leave Luffenholtz County Beach and head one mile south to Moonstone Beach. It's also known for its tide pools and rocky cliff face, but in addition it has sea caves and great surfing. When we arrived, we saw what else it has that Luffenholtz doesn't, and that is the mouth of the Little River. I'm pretty sure it doesn't get more beautiful than this.

There weren't green rocks strewn about at the base of this cliff, but there was an obvious trail up that we promised ourselves we would return to hike one day soon.
When we first saw this cliff face, we thought it would have lines and lines of fossils like the ones we always see at Capitola Beach. We looked and didn't notice anything, and just dismissed this as a possibility for fossil hunting. It was just another rocky cliff face like the hundreds of miles of cliff faces along the California coast.

When we got home from this walk, I tried to identify the green rocks from Luffenholtz Beach. I wasn't completely successful. A lot of shiny polished green stones show up on google searches. Then I emailed geologist Andrew Alden whose website and name came up when I googled this search term "Serpentine Beach Rock." He wrote me back, sent me links and thoroughly enlightened us about what we had been looking at. We had not heard of the Franciscan Assemblage (or Franciscan Complex) as this particular section of northern California's coastline is called. The geological history of it is so incredibly rich and interesting it has its own Wikipedia page. Here's an excerpt:
These rocks - which are also known as the Franciscan Complex, Formation, Series, or Group - include mafic volcanic rocks (basalt), many of which are altered to greenstone, radiolarian cherts, greywacke sandstones, limestones, serpentinites, shales, and high-pressure metamorphic rocks, such as blueschist. Although most of the Franciscan is Late Jurassic through Cretaceous in age (150-66 Ma), some Franciscan rocks as young as Miocene (15 Ma), and as old as early Jurassic (180-190 Ma) age are known. Following deposition, these rocks were then faulted, folded and mixed in a seemingly chaotic manner. Due to the lack of continuous exposures and the complex folding and faulting, it is impossible to use conventional methods to estimate the thickness of the assemblage. However, various arguments can be made that at least 50,000 feet (15,240 m) of sediment are present.
Franciscan rocks are thought to have formed prior to creation of the San Andreas Fault when an ancient deep-sea trench existed along the California continental margin. This trench, most of which is no longer evident, resulted from subduction of oceanic crust of the Farallon tectonic plate beneath continental crust of the North American Plate. As oceanic crust descended beneath the continent, volcanic rocks, mainly basalt, making up the lower plate, and marine sediments deposited on top of it were scraped off and accreted (i.e., added) to the leading edge of the overriding plate. This resulted in widespread deformation with development of thrust faults and folding. Ophiolite (which weathers to serpentine), and rocks altered by high-pressure metamorphism (such as blueschist) were emplaced during this episode. Deformation and emplacement continued during subsequent creation of the San Andreas fault to result in a complex chaotic assemblage of diverse rock types that some refer to as a mélange.
Does it blow your mind to know that this is a formation that has been around for 150 million years? There we were walking around, staring up at it, wondering about its significance, its colors, its lack of obvious fossils, and not thinking at all about unimaginable amounts of time and the fiery crazy mechanisms that thrust this piece of earth up like this. And, just because it really is a spectacular complex, it does have a sparse but diverse assemblage of fossils. We didn't see them because they are microfossils.

Just knowing how old these mountains here are, I thought I should take a look at the age of the Appalachian Mountains. Okay, our mountains here are mere babies compared to the 500 million years of the Appalachians. Roger asks, "How old is the Canadian Shield?" The Canadian what, says I? So, I take a look. Wikipedia says it's 2.45-1.24 g.a. So, what is g.a. I wonder? I suggest it probably means a gazillion years. We laugh. It's geologic time. We're talking billions of years. BILLIONS! California is so young. But that's probably because we're still forming. Stay tuned!

The best part of the internet is finding answers to our questions, and the best part of the planet is its endless awesome mysteries.

22 comments:

  1. I always liked collecting rock specimens as a kid, and was one of the few engaged students in my high school earth science class. Have read with great relish things like John Wesley Powell's journal of going down the Colorado River in boats, Muir's writing, etc. So love reading this post! Got to savor the solid rocks before the greedy people crush them...

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  2. You might be interested in a little exercise I used to do when I led walks for a company who offered walking holidays in the UK. It worked best when there were children present but adults found it equally enlightening. First you say we're going to walk back through time and you hand out little markers with things written on them like "Present Day", "1066 - Battle of Hastings", "Jesus born 0 AD", "End of Ice Age", "Dinosaurs!", "Age of the rocks we're walking on", "Age of the Earth". You put the present day one in at the start of the walk, almost immediately you shout "Stop!" and stick in the "1066" marker just one centimetre along the walk, then the "0 AD" marker another centimetre into the walk. This establishes the scale: 1,000 years = 1 cm After one metre you're at end of the last Ice Age. The age of the rocks was then usually between a mile and four miles along the trail - unless we were in certain parts of Scotland where the rocks are a similar age to the Appalachians. Your rocks in California would be about a mile and a half into your walk. At the end of the walk we were always left with one youngster still holding their marker and asking "When do we get to the age of the Earth?" "Sorry, son, but you've still got another forty miles to walk!"
    As the man said "When they made time they made lots of it!"

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  3. My son was a rock hound as a child and what knowledge I have of them comes from him. :-) How lovely to live there and have those beaches nearby, which offer delights not seen at first glance.

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  4. I love Moonstone Beach and so many others along the CA and OR coast. The rocks around the mouths of those small and larger rivers are always wonderful. Such variation. Just beautiful. The Winchuk and Chetco rivers up along the OR-CA border have some super interesting geology a bit upstream of where they meet the ocean.

    Interesting to read more about them. I'm always amazed by the serpentine outcrops that I see in places like along the Illinois River of Oregon (one which I know you would know well). To think of where and how that rock was created just blows me away.

    I'm very familiar with the extremely weather granite up on the Canadian Shield. I have some pieces in my garden here in NS - brought here from Ontario - sort of as anchors to that wonderful oldest of old geological landscapes. I have always liked to put my hands on such rocks and think of just how old they are.

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  5. this is such a wonderful post! thank you for being who you are and sharing your you-ness and the beauty of the world.

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  6. isabelita-- The richness of our planet is always so evocative and beautiful. We are lucky to be around these stunning reminders of time and space.

    John-- I loved reading this! Marking out time in miles is a wonderful hands-on way of expressing it. I remember years ago sitting with the calculator and trying to figure out how long a million seconds is (12 days), and then a billion seconds (32 years). It really helped to get the difference between a million and a billion. A trillion seconds ago, Neanderthals were still here. Time is so much fun to contemplate!

    kenju-- I can see how rock-hounding can be an incredibly wonderful way to know the world. We do feel very lucky to have made our way back to the coast.

    Bev-- You have a piece of the Canadian Shield! I would love to hold something that old in my hands. When I read the comments here, it makes me wonder how so many humans have lost their sense of wonder about the absolute splendor and beauty of this old and spinning planet.

    Maryanne-- I am so glad you liked this post. We are so happy to be out exploring and finding things that make us want to know more about everything.

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  7. Internet is awesome! I walk around up here finding amazing things. I'm reading your blog and finding amazing things. This is really interesting.

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  8. So it's called the Franciscan Assemblage. I've loved it all this time without ever knowing that. When I think of being at the Pacific Ocean, I always think of the rocks and rock formations. Love your photos and the map. Among my favorite places are where rivers meet the Pacific ocean. I feel so happy seeing Little River. Thank you!

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  9. I get totally blown away by ancient things. The Egypt display at the museum, ancient artifacts. And I'm also blown away when I stand in abandoned cemeteries here in the mountains and wonder about the hardscrapple life those early people endured. I am easily impressed by the very old.

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  10. Detective robin, you have done a wonderful job sleuthing. Isn't the Internet amazing? So much knowledge right at our fingertips.
    Cracked up at "gazillion". Sounded right to me:))
    Things hundreds of years old give me goosebumps. Being around things billions of years old takes me back to that time and I try to imagine what sort of life was there. Lucky you.

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  11. Dave-- It's so wonderful to find answers to questions, and to find things in the world that inspire us to pose those questions.

    am-- Isn't it great to put names to things that we have loved for so long? To know this history is to add even more awe to the beauty.

    NCmountainwoman-- I always think that very old things help us keep our lives in the moment in perspective.

    Arkansas Patti-- Thank you! It is the best part of the internet for me, finding answers to my millions of questions. It would be interesting to find out how old the mountains are in Arkansas where you live. Geological history is everywhere!

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  12. Robin,
    I love reading your thoughts about what you guys see. I grew up just west of the Appalachians and traveled across them a "hundred" times. We've camped (many years ago) in the Sauratown Mountains and the Uwharrie Mountains in the middle parts of North Carolina. They are such old and worn down mountains (much like me, I like to think). When our daughter lived in Greeley, CO, I would say to my wife, I prefer our old age eastern mountains to those intimidating teen-aged Rocky Mountains with their big muscles and sharp abs. A few years back, a friend who was a geology major taught me the term "uniformitarianism". Now I see evidence of it everywhere. There are so many things out there to learn in these remaining years. I relish each new experience and I appreciate so much folks like you who open my eyes to new things to look for.
    Best Regards to you and Roger.
    aubrey

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  13. The metamorphic rocks in our valley here in the northern Piedmont are 1 billion years old. I try to impress people with that fact--they're looking at, and walking on, rocks that have been around for 1 billion years--but very, very few are impressed. It would take people like Roger and you, Robin Andrea, to appreciate how really cool they are.

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  14. I appreciate so much your educating me! we have always returned home with rocks from our adventures but know nothing about them. thanks for encouraging us to be more involved in researching the things we see and love. it is so exciting to learn about our world, and your research pays off in the sky and below...great job, robin! :)

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  15. YAY! I was hoping you would be able to ferret out the geology and tell us about it. The green stones are so beautiful. Did you find out what the red ones are?

    The thing is, people LOVE learning this sort of thing about their homes. When my little adopted town of Hawley did its garden tour this past summer, they decided to focus on rocks rather than flowers, so not only did they include gardens that used extensive rock design, but they got a geologist to teach us about the geological history of Hawley. It was the best-attended tour ever. Rocks not only teach us about the earth; they teach us about the ocean, and even about the atmosphere.
    YAY! I was hoping you would be able to ferret out the geology and tell us about it. The green stones are so beautiful. Did you find out what the red ones are?

    The thing is, people LOVE learning this sort of thing about their homes. When my little adopted town of Hawley did its garden tour this past summer, they decided to focus on rocks rather than flowers, so not only did they include gardens that used extensive rock design, but they got a geologist to teach us about the geological history of Hawley. It was the best-attended tour ever.
    http://www.sciencedaily.com/releases/2014/04/140426155348.htm

    http://www.sciencedaily.com/releases/2014/04/140426155348.htm

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  16. It printed it twice! What the heck? Sorry!!

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  17. Aubrey-- Thank you so much for your kind words. I love reading about the eastern mountains and the Rockies. I've been to the Appalachians and I lived in Boulder, CO for many years. It's so interesting to perceive our planet as a spinning sphere of ongoing geological changes.

    Scott-- You walk on billion year old rocks! I love knowing that. I would love to see a photo of the rocky parts of your walks.

    Sky-- I don't know why I always want to know everything, but I do! I'm completely driven to finding answers. I am glad my enthusiasm encourages people to keep looking around and asking questions. I love this planet!

    CCorax-- I love knowing that your little town added a geologist to the garden (and rock!) tours. I think it helps us to feel more connected to our earth when we get to know what it is we are looking at and walking on, and how unbelievable long it has all been here. A truly wonderful thing!

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  18. So beautiful! This makes me want to go back out to the west coast. The combination of beach, water, and rock is just so endlessly fascinating.

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  19. jo(e)-- Yes, we understand wanting to come back. It's why we sold our place in the Sierra foothills and moved to coast. It is endlessly fascinating! Thank you for stopping by.

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  20. Formed prior to the San Andreas? wow.

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  21. I wonder what those red rocks are. This is a fascinating post, full of information.

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  22. kathya-- There are many fault lines and subduction zones. It's wild to think about some of these mountains forming before San Andreas. Here's another link that Andrew Alden sent about the Franciscan Assemblage. It has great information about how state of California came to look the way it does:
    http://www.watchingforrocks.com/2011/03/finding-franciscan-complex.html

    Hattie-- We are determined to find the names of the things that intrigue us. That's how we got to know the names of a lot of the birds we see and the beautiful cloud formations we photograph. The natural world is the best teacher!

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