Submitted by Barbara Magnuson, with help from Donn Charnley and Corinne Waters, and directions by Dale Middleton, who was guided by Mark Sundquist, president of the Ice Age Floods Institute Puget Lobe Chapter. Arm-waving geology by Dave Tucker.
May 21, 2011.
A sizable erratic is located in Edmonds. It is easy to access and about as large as a good-sized camper. The erratic is on a slope and the visible part is at least 10′ or 11′ high on the lower end. Most of the rock is weathered to a uniform dark gray but the face at the lower end is clean. There are lots of clasts (rock fragments) in the rock, which also has fine glacial striations on the surface.
Though I have not seen this rock (Dave says) this is conceivably a marine volcaniclastic rock (à la Chilliwack Group or possibly Nooksack Group rocks near Mount Baker or elsewhere), or even a welded intracaldera ignimbrite (source unkown) with included wall rock breccia clasts. I’ve added a photo of intracaldera breccia from the 3.72 Ma Hannegan caldera (North Cascades) for comparison. Anyone wishing to take a closer look and suggesting an origin for this erratic is reminded that the erratic is on private property.
The erratic is at 23121 Edmonds Way (Hwy 104) at the intersection with 232nd St. SW. Directions from I-5, north or south bound, are: 1) exit at State Highway 104 and go west about 1.2 miles past Highway 99; 2) continue another mile to 232nd St SW; 3) turn right onto 232nd; 4) go about 40 feet and note a left turn into an entrance road. The erratic is quite visible from this entry. 47°47.348′N 122°21.285′W. The Renick Printing Co. is on the left, with a parking lot behind it. This lot is private property so please do not park in it. If you see PRIVATE PROPERTY signs at the entrances to this little driveway, please respect them.