Does that get developed more in later works? I only read the first two. (Sword and Elfstones), that seemed rather peripheral to a story that was very similar to the Lord of the Rings.
I don't remember it in Sword. It's in Elfstones because they travel to the ruins of San Francisco. Apparently it is much more substantially developed later, however. I've also only read the first two
I've completely forgotten the plot of Elvestones, since I probably read it twenty years ago. I certainly don't recall the part about San Francisco.
Fantasy can be anything from anthropomorphised POV characters to allegories with abstract characters (Despair, Joy etc.) It's fine if your particular story lies between genres. You could write your story now and then pitch it to ones that accept that particular kind.