There were several of these hanging out around a colony(?) of solitary bees, mostly these large ones, a species of Nomia (Halictidae):

Size estimated--it was somewhat larger than Bombylius major, perhaps, and this estimated length would not include the proboscis. See discussion here:

---AHA!---
Insects of Torrey Pines California has an image of Heterostylum robustum which matches this in the strong abdominal pattern, most notably the big white spots on the rear of the abdomen--they were very noticeable on my fly. Also described as being a parasite of Nomia, matching the association I saw. Size is also given as 10-12 mm. I noted the fly was large, estimated at 10 mm. This is larger than many other Bombylliids.
The sinuous margin of the eye is mentioned in Herschel Raney's key. It also has diagrams from Hull, Bee Flies of the World showing antennae, eye, and wing venation. All match my photos. Interesting, Herschel lists just 2 eastern species of Heterostylum in the checklist, robustum and croceum. The first is widespread, including Georgia, and other southeastern states. North Carolina State University lists just H. robustus with 4 pinned, but no specimens from that state. I've seen a Google cached image of croceum, showing an all yellowish abdomen. Given the concurrence of abdominal pattern, size, eyes, antennae, host association, and range (apparently), I'm going out on a limb and concluding this is Heterostylum robustum. A name I see on the Internet is Bomber Fly.

Thanks for help on this. It is nice to pin down a bee-fly for once.