Abaeis mexicana mexicana
In California, this is not an easy butterfly to find. But it does turn up as a stray at times, particularly later in the year. Opler (Western Butterflies) has Acacia angustissima and Diphysia as the hosts; older books tend not to be helpful in that regard (e.g. listing Senna as a host, which is incorrect). Ken Davenport (Emmel Update, p.46) says "this species appears to be showing up in southern California much less frequently in recent years, probably related to long-term drought." I've photographed it just three times: once in Big Bear, and twice in Arizona. The "tail" distinguishes it from the similar Sleepy Orange, Abaeis nicippe, as does the "dogface" pattern, if you can see it.
This butterfly was moved from genus Eurema to Abaeis recently as part of a large study using genome-scale phylogenetic trees.