It's hard to tell from the photo. California halibut have a lateral line that arches over the pectoral fin whereas dabs have a straighter lateral line. All the juvenile halibut I've caught also have fairly also well defined white spots near the fins, at least the ones I've seen from SF Bay. Here's an example:
Most sanddabs, and certainly the three species we see locally, are left-eyed flatfish meaning that when they are layed down with the eyes on top their head is pointing left. So it's not a sand dab.
Pretty sure it's sand sole; most are generally easy to tell because of their first dorsal-fin rays which are elongate and mostly free of membrane. It's hard to tell that here because the color of the fish and fins is the same as the sand.
Thanks for all the input! I agree with Ken (and others)...seems most likely that it's a sand sole. I didn't notice any web-less spines but the eyes, jaw, and tail all look very similar to sand sole photos I found.
Just seeing this. I wasn't sure at first (before seeing responses). I thought the tail looked different. I thought perhaps petrale but petrale actually looks much different when you look at a halibut picture side by side. I had some asking about a "baby halibut" in Richmond and I said, "sand dab."