New book: Geology of the San Juan Islands

San Juan Islands geologist Ned Brown brings us a wonderful new geology guide- just in time for holiday gifts.

Ned Brown's Geology of the San Juan Islands. Chuckanut Editions, 2014

Ned Brown’s Geology of the San Juan Islands. Chuckanut Editions, 2014

Geology of the San Juan Islands is a full color guide to the geology of these beautiful islands. The book is written for the geophile of all stripes. It is the best, easiest-to-understand explanation of San Juan geology I have seen, and I urge you to spend $19 and get your own copy right now.

Ned Brown is an emeritus professor in the Western Washington University Geology Department. He has been working in the islands for decades. The complex geology of the archipelago has long inspired and exasperated geologists. Ned’s book describes the remarkable tectonic history that has repeatedly brought together unrelated rocks from around the Pacific and stacked them against each other during subduction. His color photos and detailed diagrams explain the processes and evolution of each of the rock units clearly. The book also explains how he and others have come up with this most current interpretation of San Juan Islands geologic history, by mapping rock units and faults, dating zircon crystals in the rocks, identifying fossils and correlating these with the ancient areas where these creatures lived.  Ned tells you just where to go to see the best outcrops, including all the photo locations. Among the more amazing ideas he throws out is the possible origin of the oldest rocks in the  350- to 500-million year old Turtleback Complex on Orcas Island. The gabbro and granitic rocks, once intruded deep in the crust,  may have originally intruded deep in the crust….in northern Europe! This was during the time of the supercontinent Rodinia.

The book is self-published through the Chuckanut Editions imprint of Village Books in Bellingham. The book is not yet available. Go buy a copy in the store, or write Village Books and ask them to please make the book available for on-line orders.Dave Tucker

 

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Geologic tour along the Dallas Road Waterfront Trail, Victoria B.C.

Dark dike of magma invaded a larger body of pale felsic magma. The dike was broken apart. This is at Holland Point. Photo by Glenn Jareshko.

Fascinating geologic relationships can be seen  at Holland Point.

The third geology field trip along the city of Victoria’s shore has been added to the website. This one walks the city’s south shore along the Dallas Road waterfront trail from Clover to Holland Points. The trip description is largely the work of Gerri McEwen, who just completed her undergraduate honors thesis on these rocks at University of Victoria.

The thrust fault has placed older rocks on top of younger rocks.

Southern Vancouver Island thrusting has placed older rocks in the hanging wall over younger rocks in the footwall. These terms are explained in the Dallas Road field trip.

The relationships between these coast rocks are complex. There has been repeated intrusion, faulting,and metamorphism during accretion of an island arc and offshore terranes against Wrangelia after the latter giant terrane had collided with North America. Do you know the meaning of the terms ‘hanging wall’ and ‘foot wall’? Go to the Dallas Road field trip webpage to better understand the origin of these terms.

Some of the rocks are beautiful and well worth the visit. Take your camera!

Google Earth Washington Geology Map program

Google Earth screen shot showing Skagit County, Washington, geology

Google Earth screen shot showing Skagit County, Washington, geology. Click to enlarge any image. The Eocene Rhyolite place mark is my own.

Google Earth (GE, download it here) can be a great tool for looking at landforms. Washington State’s Department of Geology and Earth Resources has prepared a set of 1:100,000 geologic map overlays for the state’s counties. Find them here. Scroll down to the very bottom of the webpage to find “Google earth 1:100,000 scale Surface Geology 3d overlays” . Download the kmz file, which automatically opens in Google Earth. The various geologic layers are listed in GE’s ‘Places’ menu. You can click the boxes to show, or hide, whichever aspect you are interested in. For instance, the default map units are opaque, and you can see no landscape through them. You can adjust the transparency of the overlay, or even hide the map colors (under the ‘geologic units’ submenu) so all you see are the welter of contacts. A tutorial video by DNR on YouTube explains usage of the Google Earth geology overlay. This uses the Whatcom county kmz file as an example.

The transparency slider.

Unit transparency slider: ‘Geologic units’ is highlighted, then click the blue box next to the magnifying lens, and tweak the slider.

The tutorial isn’t very clear on adjusting transparency, so I’ll go over that first. First, click the ‘geologic units’ box in the menu, then the blueish icon next to the magnifying glass at the bottom of the menu. Use your mouse to adjust the slider until you are happy, or at least reasonably satisfied.

GE Skagit geology, with unit polygons turned off. Lines are contacts and faults. Unit names remain.

GE Skagit geology, with unit polygons turned off. Lines are contacts and faults. Unit names remain.

GE Skagit county showing only occurences of Twin Sisters Dunite.

GE Skagit county showing only occurrences of Twin Sisters Dunite.

You may choose to use the menu to show only faults, or only unit labels, or only certain units. However, there may be a TON of map polygons associated with each unit, and each isolated occurrence of, say,

‘Darrington phyllite’ has its own box in the places menu. I’m still getting the hang of it. It is worthwhile to download one county’s geology .kmz file, and zoom out so the entire county is visible. Then you can click the various units listed in the expanded menu to see just what map unit, and where, that unit box belongs to. If you click on the name of a unit on the GE map screen, a balloon pops up with more, or less, information on the unit (see the figure below). Perhaps there will be only a tiny bit of information that is of little use, or maybe you’ll get lucky and get unit name, age, and even a reference. You can always rename units to make it easier to locate them in the places menu. Suppose you are interested in Darrington phyllite but only in the Blanchard Mountain area. You can find one of the mapped phyllite polygons on the GE image, click on the colored map polygon to see which label in the menu at left is highlighted, then rename that menu item ‘ Darrington SE Blanchard’ or whatever sort of personal label makes sense for your interests. You want to set aside some free time to play around with this program.

Burlington Hill (see page here on NW Geo FT blogs) with a unit clicked for info.

Burlington Hill (see page here on NW Geo FT blogs) with a unit clicked for info. Not all of the unit callouts will have this much information.

This is definitely a useful reconnaissance tool. These .kmz overlays take up a fair amount of space, so when you open GE you’ll need to be patient as they all load. The more county GIS layers you load into your GE program, the more slowly GE will open. You can always choose not to keep them in your GE Places menu, and access the maps from the DNR website each time instead. But then you have to tell GE not to save the overlay in the temporary places list when you close GE. Suit yourself. I use this tool a lot to help plan out field trips, so I’m the sort of person who would leave it loaded on GE in my computer.

Rock Trail, Larrabee State Park

Bud and the thin beds at the overhang.

Thin beds in the Chuckanut Formation along the Rock Trail.

I will post a full geologic guide to the new Rock Trail when the trail is formally opened on April 26th. An email subscription to this blog will deliver the news to you directly. In the meantime, please enjoy other Chuckanut area geology descriptions on my blog.

Fragrance Lake

Raptor Ridge

Oyster Dome

Clayton Beach– a layer of volcanic ash preserved in the Chuckanut Formation

A full listing of localities I describe is here. For a primer on Chuckanut geology, visit this page.

Dave Tucker

Field guide to Iceberg Point (Lopez Island, San Juans) geology

Quartz veins crosscutting the sheared sandstone at Iceberg Point. As always, click to enlarge the photo.

White quartz veins cross-cut sheared sandstone at Iceberg Point. As always, click to enlarge the photo.

I have at long last published a new geology guide on the Northwest Geology Field Trips website. This one visits Iceberg Point, the beautiful and wild southwest tip of Lopez island out in the San Juans. Your visit to Iceberg Point requires a pleasant nearly-level stroll of around 2 miles (round trip). The geologic guide visits rocks sheared by subduction and accretion and the unconformity between those rocks and the overlying till. Plus, it just a great place for a day trip.

I have been distracted for months (years!) getting Geology Underfoot in Western Washington written and sent off to the editor. I visited more places for the book than I could submit to the publisher, and this is one of the ones I had to omit. It remains a great geo-trip. Wish I could have written more than one volume, but the publishers were having none of that. Sigh. So, I’m going to gradually put some of the ‘deleted’ book vignettes on this website. Thanks to all subscribers to this website; you have apparently been patient during this long hiatus. Don’t go away!

CLICK HERE TO GO TO THE ICEBERG POINT GEOLOGY GUIDE

Geology guide to Fragrance Lake Trail (Larrabee State Park)

The Christmas Girls had just finished decorating all the sign posts as I pulled into the parking lot. Very festive! Click to enlarge.

The Christmas Girls had just finished decorating all the sign posts as I pulled into the parking lot. Very festive! Click to enlarge.

I’ve written up a geology guide to the popular Fragrance Lake trail. You’ll find it here. Even if the hike is mostly in glacial till, there are interesting stones in it, and the Chuckanut cliffs are always worth a peak. I do some armwaving about the origin of the big cliffs above the lake, too.

Online geology field trip: the Deadhorse Volcano, Skyline Divide, Mount Baker volcanic field

The last couple of miles of Skyline Divide. The Deadhorse Volcano is marked by the red pin and Hildreth’s unit designation ‘acr’. Click to enlarge.

A nearly unknown volcanic vent is exposed in cross section on a rock wall at the south end of Skyline Divide north of Mount Baker. Click here to read my on-line field guide to the informally named  “Deadhorse Volcano“. Yes, I know, winter approacheth, so chances to visit this eroded volcano are fast-slipping away. Hope for a weather break, or save this little gem until after the snow is gone next year. The snow that hasn’t fallen- yet.