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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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Book Presentation in Edmonds September 14

I will be giving a talk about my book, Geology Underfoot in Western Washington on September 14 in Edmonds.

7 PM

Edmonds Senior Center

220 Railroad Ave.

 On the waterfront in Edmonds, directly across the street from the AmTrak station. There is some off-street parking at the Center, and there is elevator access. This is the montly meeting of the Ice Age floods Institute. Free and open to the public.

I will have copies for sale, $24. Also copies of the cover poster, $15. See you there!



Jamestown S’Klallam tribe acquires Tamanowas Rock

Thanks to alert reader Wendy B. who informs us that the Jamestown S’Klallam Tribe has obtained Tamonowas Rock, near Chimacum. The prominent rock south of Port Townsend last appeared in the pages of this website in November, 2010. According to the tribe, the public will retain access to the reserve, but absolutely no rock climbing will be tolerated on the rock, which is  a sacred place in tribal histories. A trail goes to the top.

Geologically, the rock is  adakitic dacite, a type of rock generated when the  descending oceanic plate melts. Rocks of this type are uncommon in the area. Read the full report in the Olympic Peninsula News. There is some accurate discussion about the geology, and also the role the 150-foot-tall rock has played in history. According to one story, the rock served as a refuge ‘from a flood’. The only logical flood that could impact this area is a tsunami. The most recent geologic evidence for a tsunami in the vicinity is 3000 years old.

I have updated the Tamanowas Rock page to include directions for getting there.

Port Townsend-area geology group joins umbrella non-profit

Quimper Geology Group joins Jefferson Land Trust

The Quimper peninsula, Jefferson County, Washington, separates two deep bays: Port Townsend, off Admiralty Inlet, and Discovery Bay, off the Straits. The peninsula includes the sweet town of Port Townsend.

Jefferson Land Trust (JLT) is pleased to join with the Quimper Geology Group (QGG) who will now be a part of JLT. The two groups have come together because they share an appreciation of our natural world. The Geology Group’s goal is to broaden citizen’s awareness of geology, geologic issues, understanding of the land we share, and land conservation, one of JLT’s primary missions. The Jefferson Land Trust Geology Group (JLTGG), as it will be known, facilitates public lectures on geology and associated subjects, typically every other month. During the summer, the group conducts local field trips to learn, first-hand, about local and regional geology. JLTGG has an informal membership of about 150 Quimper Peninsula residents. Lectures are generally free, although donations are accepted to offset meeting costs.

Their next event will be a discussion of the Geology of Mount Baker by Dave Tucker (WWU) on Sat. Jan. 14, 2012. The talk by Ray Wells (USGS) at the last get together drew a very large crowd.

Information about the geology group’s activities will be listed at the JLT website www.saveland.org. To be on the email list to receive notices of lectures and field trips, please contact Michael Machette (JLTGG program director) at this cleverly disguised email address:         geomorph08 at earthlink.net.

Updated trip to Nodule Point & Liplip on Marrowstone Island

Concretions in Scow Bay sandstone at Nodule Point. B. Mooers photo.

For whatever reason, the webpage describing the geology at Nodule Point on Marrowstone Island (south of Port Townsend) has received a lot of visits lately. I decided to see what I’d written back in the fall of 2010. I found that somehow I had deleted the photographs. I have replaced those with the originals from Dan McShane, or new ones provided by Bob and Adena Mooers, who field-checked the original trip. The trip describes latest glacial deposits, cannonball-like concretions, and best of all for this volcanophile, a basalt dike intruding the sandstone bedrock.

Visit the webpage here.

A dike cuts sandstone at Nodule Point. B. Mooers photo.

Field trip to Beach 4, Olympic coast

Dear friends,

At long last, I’ve added a new field trip. This one investigates an angular unconformity, a disconformity, and turbidite layers at Beach 4, just north of Kalaloch in Olympic National Park. You’ll find the full story here.

This field trip is an excerpt from the book I’m writing, Geology Underfoot in Western Washington, to be published by Mountain Press.

And not one single mention of ‘erratics’ in this field trip!

Many new people have subscribed to this blog; my apologies tp you that it has taken me so long to get some new material written. I’ve been focusing writing and remodeling my home office.

Now, back to the grindstone!

Cheers, Dave

Take me to the field trip!

White Rock, a very large erratic in Hood Canal

White Rock lies just off the beach north of Hood Head on the Hood Canal. It appears to be larger than any of the erratics described on this website except for the Waterman monster on Whidbey. Click here to read the story on White Rock. It requires a stroll along the beach, or a boat trip. Thanks to Dan McShane for providing the info.

White Rock from the beach. Note high tide line, and a gull for scale. How did Dan get that dang bird to perch there?

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.

More about the dike of the Nodule Point Field Trip

I found out that the dike discussed in the Nodule Point field trip on the beach at Marrowstone Island has been previously described in two references.

The dikes [there are apparently ‘several of them’ in the area] were discussed in a Babcock, Suczek, and Engebretsen paper in 1994, and previously in a WWU MS in 1984 by L.A. Melim. Babcock and others say that Melim said that the dikes  are “petrographically similar to subaerial Crescent flows exposed near Port Ludlow”, so the Scow Bay sandstones could be intertongued with upper Crescent. It’s a good story, I’ll buy it.

I’ve added this to the field trip write up, with the appropriate references at the end.


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.