From what I understand "Santa Ana" style insulators were typically used in California in some locales for supporting higher voltage series street lighting circuits. This could be an example of such an application (it is the insulator closest to the pole on the left side of the crossarm). These are CD 178 and the majority of West Coast ones were made by the California Glass Insulator Company (Long Beach, CA) in the early teens. They sort of stand out (as you can see) on account of their "space-ship" design... We do not have notation of this photo's source however we believe it might have been a close-up cut from a Shorpy image.