Hello! I found this washed up on the beach in California. I suspected a bone because it's slightly asymmetrical and it looked like there was some skin still attached on the right side, but I can't figure out what animal it might be from!
This is the chondrocranium (skull) of a cartilaginous fish - shark, ray, skate etc. I guess there must be several suspects in California, certainly more than we have to choose from here in the UK. You could try the Ichthyology Section at the Smithsonian Institution for a full ID.