Seattle area glacial erratics

The Wedgwood Erratic, North Seattle

By Dave Tucker. December 18, 2009

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

This monster erratic , 19 feet (5.8 m) tall by 75 feet (23 m) circumference, resides in the Wedgwood neighborhood in Seattle, which is north of the University District. Doug McKeever, who teaches geology at Whatcom Community College in Bellingham, went to see it and provided the photo. Doug said the Wedgwood Erratic is serpentinized greenstone, reminiscent of the rocks in the Chilliwack Group (see the entry on Mount Herman erratics). Locally known as ‘Big Rock’ (for reasons we don’t need to expound on here) is in an informal neighborhood park near the intersection of NE 72nd Street and 28th Avenue NE.  The Wedgwood erratic even has its own wikipedia entry. If you know anything more about the geology of this erratic, please contact this website to update this entry.

Click here to visit The Leschi Park erratic ,well worth visiting. It is full of fossil shells.

13 Responses

  1. Dave,

    Hey great web site. I wanted to let you know that there are at least two other erratics in Seattle. One is in Park 2 of Thornton Creek. The erratic, about 9 x 20 x 10 feet, is partially buried in duff and soil and located about 100 yards up a side trail off the park’s entrance at NE 104th St.. and NE 17th Ave. The other erratic is known as Four Mile Rock and sits on the shoreline below Magnolia Bluff. It is noted on some city maps. And there used to be a well-known erratic in Rainier Valley at 48th Ave. S. and S. Ferdinand St. It was known as the “Big Rock.”


    • David,
      Thanks for telling us about these. What happened to ‘Big Rock’? Perhaps a Seattle-area reader of this website can visit the Seattle erratics and send in a story.
      For readers who don’t know, David Williams is author of ‘Stories in Stone- Travels through Urban Geology’, a most excellent, highly recommended read (I must add it to my Geology Field Guides page). The book describes the geology of some of the most interesting building stones in America. It includes the Indiana Limestone, which you can see at the Bellingham Federal Building. He also wrote ‘The Seattle Street Smart Naturalist’. He has a great urban geology blog at

    • There is a erratic off trail in Seahurst Park also

    • Thanks Ryan. Photos? How large? Easy to find?

  2. Hi David and others;

    The Big Rock at 48th Ave S and S Ferdinand St in Seattle is still there, it is just a bit smaller than its original size. Look for it in the second lot east of the intersection on the south side, where it forms a large chunk of the embankment. I do not know the specific history, but I would guess that some of it was blasted away for real estate development.

    There are numerous smaller less impressive but still substantial erratics a bit to the east at Ferdinand St Park on Lake Washington. A half-dozen or so are found in plain sight, some off shore and some on shore. There are also several in Seward Park across Andrews Bay from Ferdinand St Park. In Seward Park, there is one directly across from the amphitheater, another a bit north down a slope on the west side of the upper loop road just before you reach the main ‘Spine’ trail (service road) entrance into the forest, and another on the Erratic Trail, a side trail off the main trail (ask for a trail map at the Seward Park Environmental and Audubon Center, or print your own from the Comprehensive Trail Plan found here: )

    There is also what I am pretty sure is a small erratic next to the bench near the swimming dock storage area on Andrews Bay. I believe there is another at bit south of the northeast corner of the park on the upland side of the outer loop road, somewhat hidden in the vegetation. There are probably others as well.

    While I’m pointing out erratics in Seward Park, I should mention the new trail to the Earthquake Fault Scarp on the east side of Andrews Bay. This scarp is viewed as a ‘minor’ fault in the Seattle Fault Zone. I’m guesstimating the fault scarp is at least 30 feet high (it looks higher from on top), but I have not yet tried to measure it. Guesses as to its age (presumably postglacial) and the history of the rocks involved are welcome. Informed opinions about whether the nearby bluff on the south end of Andrews Bay is part of the same or a different fault, or is not a seismic feature are also welcome.

    • Paul,
      Thanks very much for your comment. Would you like to write up a description of some of these Seattle area erratics, with directions, what you know about the rock type, possible sources?
      You may contact me at

  3. We recently uncovered an unusual erratic in Upper Leschi Park above Lake Washington Blvd. The entire rock is embedded with fossilized bivalves. Would love to know where it came from!

  4. There appear to be several (10, perhaps that I’ve seen) erratics along Kamber Road in Bellevue. Both sides of the road. Kamber Road is just a few blocks long – can’t miss them. If stacked 3 high they’d look like snowmen. The one in my back yard I’ve looked at for nearly 30 years wondering why someone would lug such a plain rock where it sits. They’re not great landscape stones, and are too big to haul out, so we plant things next to them to hide them.

  5. Hi,

    I just read the article on erratics in the National Geographic. When counting Seattle erratics don’t forget the big rock at the South Seattle Community Collage aboretum. alittle farther afield is the big rock at Big Rock Road just south of Carnation.

    • Both these rocks are featured on this website. Go to the ‘Field trips’ tab, scroll down to ‘erratics’ and find the link to those big erratics.

  6. […] also ferried along boulders of various sizes, known as erratics. Seattle’s most famous is the Wedgwood Erratic, though others still persist and many other were blown up by settlers. (Plymouth Rock is the most […]

  7. […] were getting ready to blast it as part of a grading project on Madison. (There used to be another “Big Rock” in Seattle but it suffered a similar though less destructive […]

  8. I went ahead and put all of the erratics mentioned here into a google map so that people can easily find them! Feel free to add/edit.

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