Appeal to citizen scientists: Do you know of any Jackass conglomerate erratics ?

Adena Mooers and a Jackass conglomerate erratic, Pt. Wilson. Photo courtesy A. Mooers. Click to enlarge

Dear readers,

Have you seen erratic boulders of Jackass conglomerate? I’m specifically interested in learning of any sightings south of Whatcom County, on either side of Puget Sound, or on the shores of the Strait of Juan de Fuca. The easiest place to spot them is on beaches.There’s an idea out there that all these rocks came down to the lowlands only during the last phase of the Pleistocene continental glaciation, the Sumas stade of around 11,000 14C years BP (before present). That glacial advance apparently didn’t get any further south than Bellingham, so if Jackass boulders are found to the south, then that hypothesis must be rethought. I am aware of a Jackass erratic on the beach at Port Townsend, which in itself casts doubt on this hypothesis. Examples of Jackass conglomerate erratics have previously been discussed, with photos on this website: Donovan Avenue erratic, Bellingham; Aldergrove erratic, BC; Malloy Village erratics, Ferndale; H Street erratic, Blaine.

In any case, these are really distinctive conglomeratic boulders that originated up the Fraser River valley, either east of Hope near Manning Park, or in another area considerably further north, around Lillooet. If they are present in deposits predating the Sumas, for instance in Everson glaciomarine drift or Vashon till, then we can say with certainty that the ice that formed the glaciers of the last glacial maximum, terminating south of Olympia, came out of the interior of BC via the Fraser valley as well as the west flank of the BC Coast Mountains. This is the most widely accepted idea, and will be well-demonstrated if the distinctive Jackass boulders are found beyond the Sumas stade deposits in Whatcom County .

If you spot one of these cool boulders outside of Whatcom County, please send a photo, directions, and GPS coordinates (be sure to specify what coordinate system you are using) to me:

email contributions to this address.

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2 Responses

  1. Dave

    I have seen Jackass rocks on numerous occasions on the shorelines of Jefferson County. Not sure I have any pictures, but I have seen them frequently. I’ll try to document them next time. Interesting concept that likley needs rethinking.

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