Possibly Gravenstein. It's very common on the central coast of CA.

Here is a link that might be useful: pictures Gravenstein apple

I was thinking the same but wouldn't that be way too late for ripening?
Or... When what the pic taken?

Thanks for the responses. I took the photo yesterday, Sunday, 28 October. It is late season for this apple. There are only 5-6 apples left, and they are more yellow than green as they were earlier in the season. I'm attaching a photo of the tree (also taken yesterday). There are 2-3 apples at the top of the tree. The tree is at least 10 feet tall, if that information helps at all.

Gravensteins ripen so early that they are not offered for sale in early October at a major apple festival.

I have been offered ripe Gravensteins in late August at family reunions.

Sierra Beauty? one of my favorite apples, everyone should have one. Keeps forever, delicious flavor, good for pies and fresh eating.

Carla in Sac

Carla in Sac,
Thanks for the response. That might be the one. That tree produces the best apples.

Find someone to graft you a couple of new trees using scion wood from that tree. That's the only way you can guarantee you get the same fruit.

To: Oregonwoodsmoke
Thanks for the suggestion. We plan to try grafting onto a gala apple tree in the same yard. The gala tree looks healthy, but it hasn't produced many apples. It's also quite young. We've read a bit about grafting, and I believe that Spring is the time to do it. I would appreciate any advice about when and which grafting method.