It looked quite young — relatively short overall length, with broad blades, and a small holdfast.
When I looked more closely, I was intrigued by the holdfast:
Can you see that the holdfast is attached to a small pieced of wood?
It might be easier to see this from below:
I wondered about the history of this kelp. Did it start growing on a piece of wood that was lodged in rocks somewhere and then part of the wood broke off and washed ashore? Or is it possible the kelp started growing on a small piece of floating driftwood? Have you noticed Feather Boa Kelp growing on wood before?
P.S. I laughed when I read the description of juvenile Feather Boa Kelp on the California Seaweeds eFlora website. It says they look like lasagna noodles. A fun description of those broad, ripply blades!