Coyotes would have made more of a mess. The puncture wounds on your hen's neck and the fact there was very little blood on the others makes me think weasels. They will bite the neck or under the wing and then lap up the blood. I lost a bunch to a weasel during the night several years ago. The missing ones, however, to not make sense for it to be a weasel. At least not around here. Ours are too small to carry off a chicken. A mink, however, is big enough to carry them off and part of the same family is a weasel, so maybe it was a mink. I doubt it would have been both, but you never know. I don't know if a mink will bite them then drink the blood also, but I suppose it's possible.
Sorry to hear about your losses. I would say weasels too. If you left the coop open, some of the hens may have run out and gotten as far away as possible and could have died out in the woods somewhere. Either that or maybe larger weasels, like fishers, dragged some out to feed their young.
No fisher's in CA. Just up here with us in the cooler climates. I would bet it was a coyote or a dog, maybe a gray fox. Grey Foxes are native to your area and this time of the year will kill surplus and drag back to a den to help with feeding kits. The only other reason some may be missing is that they fled during an attack. But they would be found either as victims or returning home within a day or two. Who knows. I am sorry for your loss. I hope to never go through it.
we lost all our chickens in one night also, the heads were gone, just bodies left....we moved them from one place to another, 2 nights prior due to 5 being killed in one night, fixed a barn stall wired it well and something got in and it was a massacre. We are so hurt, our farm is so lonely without our girls running up to us during the day looking for any extra tidbits, we have set weasel traps for 4 nights, nothing...but of course all the chickens are gone, so why would it come back...we have 1 game hen that was out that night, she survived...
Have y'all trapped for skunks? Skunks in Texas can knock out half a dozen chickens by itself(the entire thing!!), more if she's with her kids. They also kill any others that may sound an alarm. They have the same mouths as minks, their bites are easily mistaken for one another.
So sorry about your loss. I can't imagine being without my girls. ):
They have live traps available. The best way to lure them is a can of anchovies opened 1/3 of the way so they have to go inside to get the treat not just reach through the holes and get away. Yes they will eat just heads. We have had them just rip out throats then take what they wanted. They'll eat beak, bones and all.
I'm beginning to think that after the wire was chewed through to get the bait , instead of the vermit crawling through the 2in hole at the other end of the trap.