This is a useful resource for California and beyond as it has a keys to:
1) the genera of Bembicini of North America;
2) the species of Bembix
3) the 10 species of Bicyrtes
in North America;
4) the 7 species of Microbembex
in the continental US.
[Caveat: I'm an amateur and can't competently comment on how much change may have occurred in Bembecine taxonomy since this publication in 1971. But, shortly after posting the above, I found a reference
discussing at least two California species not known in 1971: Stictiella villegasi
described by Bohart in 1982, and Microbembex elegans
described Griswold in 1996.