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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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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.)

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!


Cougar Divide field trip updated


Pale dikes intrude Nooksack Fm. at the head of Dobbs Creek.

I hiked Cougar Divide again on September 12, and have updated the field trip guide. You can read it here. This is the easist and best place in the area to see intrusive dikes.

The updated guide includes these changes: better directions to find the oldest dated rock in the Mount Baker volcanic field, a rhyodacite dike, and the GPS coordinates have been changed slightly; a new photo added showing the dikes at the head of Dobbs Creek.

The ridge is beautiful. I noticed that there was some hoar frost on the trail in a few places, and there are patches of fresh snow on the snow slopes below Chowder Ridge. Take an ice ax to reach Chowder, as there is a short section of firm, steep, and exposed snow to cross just below the ridge.

Additions to the Chuckanut fossil gallery at WWU Geology

Tracks of a heron-like bird in the Chuckanut Formation. Thanks to the anonymous woman who allowed me to use her finger for scale.

A number of new rock slabs with fossilized foot prints of Eocene animals have been added to the Chuckanut fossil display at WWU. Visit the webpage on Northwest Geology Field trips.

The exhibit contains new sets of tracks of the giant flightless bird Diatryma, carnivorous creodonts, herons, tapirs, and a goose-like bird, as well as a Diatryma skull reconstruction and two original Eocene dioramas by Marlin Peterson.

Go straight to the webpage.

Field excursion to the giant Capricorn Creek debris flow, Lillooet River valley, British Columbia


View to west. The Capricorn debris flow descended Mount Meager's east flank into Meager Creek, jogged north slightly, then spilled down Lillooet River (foreground). The BC campground is just out of view at bottom right. Click to enlarge, Photo T. Spurgeon


Terry Spurgeon has contributed another field trip to this website. This one visits the distal deposits of the August 6, 2010 Capricorn Creek debris flow, one of the largest observed in Canada’s history. This flow initiated high on the east flank of Mount Meager, an active volcano west of Pemberton, BC. The flow entered Meager Creek and blocked it, then surged into the Lillooet River valley, leaving behind a devastated zone of mud, boulders, trees, and ruined roads and bridges.

Columnar jointing in Washington

By Dave Tucker  September 29, 2010

The most recent post on the entertaining Magma Cum Laude blog, by Jessica Ball [aka ‘Tuff Cookie’] states:

“Perhaps we should submit a request for a Columnar Jointing Week to someone in Washington.” Maybe she means a Presidential dictum for ‘National Columnar Jointing Week’.

Okay, well, I’m “someone in Washington”– State, that is. I can’t issue any dicta whatsoever, so will reinterpret her ‘challenge’ to show off some photos of columns from Washington State. This won’t be a field trip on the Northwest Geology Field Trips website just yet. I’ll work these various stories and photos into future field trips. Click any photo to enlarge it.

Pinus Lake andesite, Mount Baker (Hildreth and others, 2003). I already wrote up a field trip to this orphan andesite lava, with the spectacular columns rising above the Mount Baker Highway. Here’s the photo again.

The 300-foot-thick Pinus Lake lava towers 600' above the Baker Highway east of Nooksack Falls. Click to enlarge any photo

Here are some more andesite columns, in the Table Mountain lava flows of Heather Meadows near Mount Baker. This flow is similar in age to that of Pinus Plateau, around 300,000 years old. It erupted from a vent on Ptarmigan Ridge, and forms the inverted topography of Table Mountain between Mount Baker and Mount Shuksan.

Stubby, 1-meter-wide columns in Table Mountain andesite along WA 542 below the Mount Baker Ski Area.

The Table Mountain lava (Hildreth and others, 2003) has stubby columns at the lowest elevation exposures, shown above. However, higher up, the lava has much skinnier columns, suggestive of cooling in contact with ice. Just above the Heather Meadows Visitor Center (USFS) are these wonderful columns right along the highway. They cooled against the steep valley wall. The radiating columns show that the cooling front was spreading out into the interior of the flow.

Cooling fractures define these columns in the Table Mountain andesite. The radiate into the interior of the flow from the outer edge of the lava.

And how about these ice contact columns? These are in the 70,000 year old Portals andesite on the north wall of Rainbow Creek at Mount Baker.

Crazy divergent glassy columns in a flow that cooled in contact with glacial ice 70,000 years ago, Mount Baker volcano.

Now, lest you think I am completely Baker-centric, here are some columns in a dacite lava near White Pass, south of Mount Rainier. These are in the Clear Fork Cowlitz River, and can be seen from a small interpretive site along US Highway 12 west of White Pass. The glaciated flow is around 650,000 years old (Pringle, 2008).

Clear Fork dacite, US 12, 2.3 miles east of the junction with WA 123. Columns are 650 feet high!

And then there is Beacon Rock, the 57,000-year-old (Evarts and others, 2009) eroded plug along the Columbia River just west of Bonneville Dam. The colonnaded south face of the rock rises 850′ above the river. The cinder cone that once surrounded this basaltic andesite plug was eroded by the catastrophic Missoula Floods.

Big columns on the south face of Beacon Rock, seen from the boat launch just to the west along Washington 205.

Of course, the Columbia River Basalts provide quintessential examples of columns in Washington State. Here are some in the Grand Coulee, on the west shore of Lenore Lake (US 97).

Several stacked flows in the Columbia River basalts, Grand Coulee.

Here’s a detail of the wildly diverging columns in the lower right of the photo above:

As thick lava cools, cooling fronts migrate into the interior of the flow. These columns are bounded by fractures which grow inward from cooling into the hotter part of the flow.

The Columbia River Basalts flowed out the ancestral Columbia River and radiated into southwestern Washington, too. Here are some columns in a quarry near Rainbow Falls State Park, which are west of Chehalis on US 12.

CRB columns in the Chehalis River valley, Western Washington.

So, I’ve done my part to answer Tuff Cookie’s challenge. How about…Oregon? Or is it a matter of ‘seen some, you’ve seen ’em all?”


Evarts, R. C., Conway, R. M., Fleck, R. J., and Hagstrom, J. T., 2009, The Boring Volcanic Field of the Portland-Vancouver area, Oregon and Washington: tectonically anomalous forearc volcanism in an urban setting. In Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacific Northwest, ed. J. E. O’Connor and others, 253-270. Boulder, Colo.: Geological Society of America.

Hildreth, W., Fierstein, J., and Lanphere, M., 2003, Eruptive history and chronology fo the Mount Baker Volcanic Field, Washington: Geological Society of America Bulletin v. 115     p.729-764.

Pringle, P., 2008, Roadside Geology of Mount Rainier National Park and Vicinity. Washington Division of Geology and Earth Resources, Information Circular 107.

Racehorse Creek landslide field trip

A hiking field trip to the complex deep-seated Racehorse Creek landslide of January 7, 2009 is now available for your geological pleasure.