Flat deflated blades, usually in pairs at the tips, with a prominently visible spine and a bumpy surface.
Rockweed (Fucus distichus)
Washington Park, Anacortes, Washington, USA 4 Dec 2004
I think this is Rockweed ... a species of brown alga in the family Fucaceae to be found in the intertidal zones of rocky seashores in the Northern Hemisphere.
Another very common seaweed at North Beach: Fucus gardneri (Rockweed).