Large waves during the past week have washed lots of seaweed onto the beaches. Pictured above is Red Opuntia (Opuntiella californica) — named after prickly pear cactus (Opuntia spp.). Note the distinctive growth form, with spreading branches of rounded blades.
P.S. I had no idea — Do you know how many different species of prickly pear cactus can be found in California? Any guesses? The answer is: Fifteen! (There's only one species of Opuntiella in the state.)