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    Northwest Geology Field Trips, by Dave Tucker, is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 United States License. You can use what you find here, repost it with attribution to the author, "remix" it for your own purposes, but may not use it with the intent of making money off of it.

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Geology Underfoot: BOOK SENT TO PUBLISHER!

DT and the Geology Underfoot in Western Washington files. You will get to read it on paper, soemthing I've yet to see.

DT and the Geology Underfoot in Western Washington files- all on one flimsy bit of plastic. You will get to read it on paper, something I’ve yet to see. Chico stands guard my monitor. Photo by Kim Brown.

I finally completed the manuscript of Geology Underfoot in Western Washington. The sum of the last three years of my life was copied onto a DVD and sent off to the publisher today – 423 files including chapter text, photos, diagrams, and maps. There are (at this point) 22 self-guiding field trips, plus a lengthy Introduction that is a primer on plate tectonics, a capsule history of the geologic history of western Washington, a bit about petrology, and how to date a rock (“You need to be a little boulder” says Kim.) Groan. I promise I do not use that pun in the book, but there may be a few other gneiss ones. (Sorry). OK, now my editor James Lainsbury at Mountain Press Publishers gets to hack away. He’ll send it back to me for what I’m sure will be shortening, revisions to some of the figures I made, and who knows what else. The book will be on bookshelves in 2014 unless James says ‘This sucks. Start over.’ Thanks to all the people, geologists and ‘civilians’ alike, who read and field checked the chapters.

You can read a sample chapter (pre-editing) and learn more about the book here on my website.

So, time for a beer. Well, maybe a nap first.


Adakite near Chimacum, Washington

Tamanowas Rock rising above the access gate. Peninsula Daily News.

Dan McShane has posted another neat geological location on his website, Reading the Washington Landscape. He visits an exposure of an oddball type of felsic lava and pyroclastics, adakite, at Tamonowas Rock, near Chimacum, a little south of Port Townsend. It’s not really a field trip, because his post doesn’t give much in the way of directions, or describe the outcrops. Use the Google Earth map on Dan’s post to find the trailhead; the east facing rock cliff rises just to the west of the road. Dan’s photos look pretty neat. I’ll definitelyvisit this place, probably when I investigate the basalt dike nearby at Nodule Point, which both Dan and I have written about previously.

Until I know more, I can expand only slightly on Dan’s post about Tamanowas Rock. This is a cliff of Eocene subaerial adakitic lava and lava breccia just west of the town of Chimacum. Adakite is a type of lava similar to dacite, and is interpreted to be derived from the melting of subducted ocean floor basalt. Generally, lavas (be they basaltic, andesite, dacite, or rhyolite) that erupt in convergence zones, such as Cascadia, are believed to result from partial melting of the wedge of the mantle (not the descending ocean plate) that lies between the subducted ocean slab and the overiding continental plate. However, there is evidence that small amounts of the subducted ocean floor basalt itself may also melt and add a recognizable trace element signature to some rare erupted products. The pyroclastic rocks exposure at Tamanowas consists of angular clasts of hornblende dacite up to one meter in diameter in a fine-grained matrix. Dan has a link in his blog’s post to a 2004 GSA abstract written by undergraduate geology students in Jeff Tepper’s petrology class at University of Puget Sound. Jeff regularly involves many of his students in petrologic research, pretty cool for an undergrad program! A number of their projects have been published. Another link on Dan’s post will take you to more than you could ever want to read about adakites. A news article on the S’Kallam tribe’s effort to protect the rock, sacred to them, appeared in the North Kitsap Herald in April 2010. A search using ‘Tamanowas Rock’ will net a number of websites dealing with this land issue. A Peninsula Daily News article with photos is here. I’ve borrowed some of theirs for this little post, with credit.

So, stay tuned for an eventual field trip guide to Tamanowas Rock to be published on this website.


The gated road at the access point. Photo Peninsula Daily News.

Beach walk geology trip at Marrowstone Island, Jefferson County.

A field trip written by Dan McShane is now posted. Originally appearing on Dan’s Reading the Washington Landscapes blog, I got his permission to post it on Northwest Geology Field Trips, and you’ll find it here. This looks like a fine low tide beach walk, south of Port Townsend. A unique feature on the trip is an Eocene dike of basalt that intrudes marine sandstone. That alone is worth the trip, but there is a lot more to see. Plus, Dan tells me, solitude is to be expected.

The dark rock at left is a basalt dike, in contact with lighter sandstone at right.