I'm in Stockton,Ca. Last year these just appeared in my backyard..they came back this year and are bigger than last year.also in a few more places... they didn't flower last year.maybe I will get flowers this year. I'm thinking they're some sort of lily.
I'm not so sure, it could be one of the Arum, e.g. Arum italicum a Mediterranean plant (probably an old cultivar), which it is now considered invasive (also in CA): See https://www.invasiveplantatlas.org/subject.html?sub=13931.
If it is not an Arum, I thin it is still in that family (Araceae), like Calla. As you see, the flowers are not very visible, but with a easy to recognize form (spadix). In my experience, "wild" Arum tend not to flower every year.