Ok, it's taking up most of the picture. I believe this is a Sharpnose Crab (Scyra acutifrons). I saw one in Seattle in Jan, but this is my first one in CA.
Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition auf dem Dampfer "Valdivia" 1898-1899. bd.6. AtlasJena,G. Fischer,1902-40.biodiversitylibrary.org/page/6307622