Here's another perspective (below). This view is of the underside:
Any guesses yet? I'll zoom out a bit more and show about half of the animal:
Okay, now here's the entire thing:
Did you guess jellyfish? This is a Purple-striped Jelly (Chrysaora colorata, formerly Pelagia colorata).
According to the Light & Smith Manual (2007), this species "regularly washes ashore on the beaches of Southern California and is occasionally found as far north as San Francisco and Bodega Bay."
From a distance, when I saw a large jelly washing up on the beach, my first thought was that it was going to be a sea nettle (Chrysaora fuscescens). Sea nettles are the most common of the large jellies in this area, but they are more brownish overall and lack the dramatic purple stripes of this species.
The bell of this Purple-striped Jelly was ~15-18 inches across. I didn't have a ruler at the time, but here's a picture with my Xtratuf boot (size 6.5) for scale.
I'm wondering if this Purple-striped Jelly might have drifted north with some of the warm ocean water that we've been experiencing recently?
It looks like there's warm water to our south and offshore. You can look at sea surface temperature maps at different web sites. Here are two examples:
Have you seen Purple-striped Jellies in Bodega Bay before? If so, I'd love to hear more about your observations.