Yes, it is. See Butterflies of California

I was wondering if that was a possible ID, as this has such prominent orange projections. None of our other specimens on B. philenor in the guide has those, but once I started investigating further I found there are other images on the web that do (see the last image on this page). I think the very long tentacles on T1 must be more important for ID.

The only county highlighted on their map in CA is Los Angeles County, which is hundreds of miles away from the host plant's native range, and even farther from the location where the photo was taken. The HOSTS database has only one record from anything other than Aristolochia- and that's on Citrus in Brazil.

I suppose there could be a population of introduced butterflies on introduced plants (we do, after all, have Gulf Fritillaries on Passiflora), but I don't think there are many Aristolochias in cultivation here- the only one I've ever seen was an Aristolochia californica at Rancho Santa Ana Botanical Gardens (the same one responsible for CalFlora showing the plant being found in Los Angeles County). I've been meaning to get a plant of it for my yard, but none of the local native-plant nurseries carries it.

Battus philenor, on the other hand, can feed on other hosts, so it's widespread in the state.