Evolution of the Puget Lowland, last 20,000 years

Animation of the advance and retreat of the last great glaciation in the Puget Lowland is available on the Burke Museum’s YouTube channel. Thanks to reader ‘Deb’ who notified me that the link in the ‘Lake Stevens Erratic- the largest in the US?’ page was broken. It’s been repaired. The animation is based on a model by Ralph Haugerud of the USGS- see the very end of the animation for full credits. Unfortunately, the model is only for Puget Sound, and does not include the San Juan Islands or points north. The source of the glacial lobe is not shown- the interior of British Columbia, the BC Coast Mountains, and the Canadian Rockies. The diagram shows the bigger picture, which has a chapter on glacial erratics, and another on the history of glaciations in the lowlands of western Washington.


Diagram from my book,Geology Underfoot in Western Washington showing sources and paths of ice related to the Vashon Lobe. The glacial tongue reached its maximum extent south of Olympia around 16,000 years ago.

This animation is a bit different from the original. This one shows events in the Lowlands following retreat of the Vashon glacial lobe, such as the Osceola Lahar from Mount Rainier 5600 years ago that reached the salt water Duwamish Embayment near Auburn, and local rebound of the crust from the weight of the ice.

If anyone finds broken links anywhere on this website. please notify me by way of a comment on the page. If you know if a replacement link, please include that.

Guided Geology Field trip to Point Whitehorn, Whatcom County

Looking south at the Point Whitehorn Reserve beach. The erratic in the foreground looks like Jackass Mountain conglomerate. Rock from this formation gets around!

Looking south at the Point Whitehorn Reserve beach. The erratic in the foreground looks like Jackass Mountain conglomerate. Rocks from this formation get around!

I will be leading two geology walks along the cobble beach and shoreline bluffs at Point Whitehorn in Whatcom County.

Saturday, June 6   1 p.m. and 3 p.m. [the same walk, twice].

Highlights: Erratic boulders, lag deposits as coastal bluffs erode; glacial strata in bluffs. We will look for marine shells in the glacial deposits, to determine if this is a submarine deposit.  See a virtual field trip posted on Northwest Geology Field Trips website.

Getting there: From I-5 Exit 266, drive west on Grandview Road 8.5 miles.  Follow the road as it curves left and becomes Koehn Road. Continue 0.5 miles to a parking area on the left. There is a 3/4 mile accessible trail through lowland forest, including a sizable (by modern standards) grove of large spruce, to overlooks atop the bluffs, with nice polished dunite benches. The trail then switchbacks 75′ down to the cobble beach. MEET ON THE BEACH FOR THE FIELD TRIP

Glacial erratics litter the beach at Point Whitehorn.

Glacial erratics litter the beach at Point Whitehorn.

This is all part of the Whatcom Land Trust and the Cherry Point Aquatic Reserve Citizen Stewardship Committee event titled “What’s the Point?” from noon to 4 p.m. on Saturday, June 6, at Point Whitehorn Marine Reserve, part of the larger Cherry Point Aquatic Reserve. A negative tide will allow for intertidal zone exploration in an extraordinary stretch of shoreline teeming with wildlife.

Kids will enjoy the hunt for shell fossils at Point Whitehorn's glacial deposits. No guarantees!

Kids will enjoy the hunt for shell fossils at Point Whitehorn’s glacial deposits. No guarantees!

Naturalists with North Cascades Audubon Society, Koma Kulshan Chapter of the Washington Native Plant Society and more will be stationed along the wooded wetland trail. Marine life specialists will be on the beach providing information about plants and animals in the reserve’s intertidal zone.

Here are some details about the event:

-The event runs from noon-4 p.m. Low tide is at approximately 2:30 p.m. We are asking naturalists to please arrive at 11 a.m. or shortly thereafter. There is plenty of parking but please consider carpooling! We heard from County Parks that there can be up to 200 people on any given Saturday in June.

-We will be providing a “species checklist” for kids to bring along the trail.

-We will have informational booths in the parking lot, and will also be handing out Pt. Whitehorn stickers and a limited supply of chocolate chip cookie ice cream sandwiches donated by Acme Ice Cream. (Plus popsicles for non-dairy folks.) There will also be a water jug and a handwashing station available.


Dave Tucker, geology

-Bob Lemon, intertidal zone

-Lyle Anderson, native plants

-Bert and Sue Webber, marine biology

-Pam Borso, Audubon

-Paul Woodcock, Audubon (will arrive around 1 p.m.)

Glacial erratic inventory website open for business

White Rock, Hood Canal. Not in the inventory yet. Many of the erratics on the Northwest Geolgoy Field trips website aren't listed (yet). Maybe that is your job!

White Rock, Hood Canal. Not in the inventory yet. Many of the erratics on the Northwest Geology Field Trips website aren’t listed (yet). Maybe that is your job!

The Washington Glacial Erratics website has re-opened for business. Managed by the undergraduate GeoClub within the Earth and Space Sciences Department at the University of Washington, it is an inventory database and map showing “significant erratics (i.e., large, diameter >8-10 feet , or has a unique composition or features)” in Washington State. Anyone can add their favorite glacial erratics including photos and a description. You will need to know coordinates (UTM or Lat/Long). Visit the website at http://waglacialerratics.ess.washington.edu/ At present (February 9, 2014) there are 12 erratics shown. Get busy!

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!


Washington Erratics website temporarily down

Dear friends,

The new Washington Erratics website is temporarily down while a glitch is dealt with. Please do not send in new material until further notice. Anticipated reopening date is November 1. I’ll send out a post when the webmaster there gives me the thumbs up. http://waglacialerratics.ess.washington.edu/

Martha Lake erratic is all cleaned up!

Greg shows off the cleaned-up Martha Lake erratic. Spic and span! photo courtesy of Greg Kulseth. Click to enlarge.

Greg Kulseth reports this morning that the graffiti has been removed from the Martha Lake Erratic at Martha Lake Airport Park. The Snohomish County Parks Department also put up an interpretive sign about erratics: where they come from, how they get swept up into glaciers, and the extent of the last glacial maximum. The sign mentions the Lake Steven’s Erratic, and states that it may be the largest in the US.
Special thanks to David McConnell of the Parks Department, who, last I heard, was going to spearhead the cleanup, and to Greg for sending the good news.
I’ve updated the Martha Lake erratic webpage to show the now-cleaned up boulder.
Looking at my calendar, I see it is ‘Spring’. Looking out my window- hmmm. Oh, there’s a new snowdrop blooming, and maybe a leaf bud! Guess the calendar isn’t that far off, and the precession of the equinox marches on.

Have a good spring!

Coupeville’s Big Rock in the news

Big Rock. Island County Commissioner Angie Homola and her daughter Kira. Angie says she is 5 ft tall, so the erratic is about 22' (6.7 m) tall. 2010 photo by Dave Tucker.

Big Rock in the 1960s. Photo courtesy of Donn Charnley.

The big rounded erratic in Coupeville has recently been the subject of debate. The town council considered a proposal to purchase the land the erratic sits on to protect the rock from possible destruction. Their was concern that the owner of the apartments behind (to the west) of the rock would consider ‘removing’ the boulder to make room for a new and larger apartment complex. Here is the story in the Whidbey News Times. An earlier article in the paper, including information from UW glacial geologist Terry Swanson, describes the rock and the property ownership issue. The second article also reveals that at least as late as the 1930s, a stairway allowed access to the rock’s summit. Note that the newspaper refers to the big hunk o’ greenstone as ‘granite’, though a much earlier story in a rival newspaper (South Whidbey Record), identified the rock correctly in an article about erratics featuring Terry Swanson.

The Wedgwood erratic is on a lot cared for by the neighborhood.

Thanks to Valarie Bunn of Seattle’s Wedgwood neighborhood for supplying these links. She wrote about the similar Wedgwood erratic in her Wedgwood history blog.

Thin en echelon dikes in the Highline Community College erratic; AND a National Geo ‘erratics’ article

The granitic erratic at Highline Community College. Photo by Bud Hardwick.

Bud Hardwick sent photos and geographic information about a large granitic erratic (yes, another one of those dang things) at Shoreline Community College in Des Moines (Washington!). I looked closely at his photos and made some deductions about the geology. Take the virtual field trip to this erratic elsewhere on this website. The rock is notable because of the textbook en echelon dikes running the full length of the big erratic.

Also, the latest National Geographic has a photo essay on glacial erratics by Fritz Hoffman. Alas, none of the ones describe n this website or any others in western Washington are included, not even the Lake Stevens Monster, the largest in the whole country. See  the photos here (an NPR website).

Beach erratic in Des Moines (the one in Washington, not Iowa!)

Last spring I put out a call for intrepid readers to investigate a reported Jackass conglomerate erratic on the beach at Des Moines, between Burien and Federal Way. Thanks to Sandy Bowman and Bud Hardwick for independently investigating. Turns out the large rock is granitic, not conglomerate. Read the article.

Consuelo Larrabee at the Des Moines erratic. Photo by Sandy Bowman.

By the way, does anyone know how I can share Google Earth .kmz files on this website? If you do, contact me via email with instructions:

email address to send reports and photos. I'll credit you.

Jackass erratic emerges from the bushes in Blaine, Washington


The H St erratic is about 2 m high. K. King photo. Click any photo to enlarge.

Northwest Geology Field Trips subscriber Kitty King of Blaine alerted me to a 2-meter-tall glacial erratic in Blaine, which recently emerged when brush were cleared along H Street Road. See the field trip description here. The 2-meter-high rounded stone is one of those wonderful conglomerate boulders from the euphonious Jackass Mountain Formation in southern British Columbia.