I think this is Five-ribbed Kelp Costaria costata

I found David Jamison's web site EXPLORE PUGET SOUND HABITATS AND MARINE LIFE to be extremely useful in figuring identifications.

www.pugetsoundsealife.com/puget_sound_sea_life/Five-ribbe...

A nice beach walk with Mary Ellen while we had a -3.06 feet Low Tide
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