Neat little Chalcidoid (actually rather large for a Chalcid wasp), taking nectar from Lepidospartum squamatum (Scale broom).

Doug Yanega (Dept. of Entomology, Entomology Research Museum, UC Riverside, Riverside, CA) provided the ID, and the following information:
This is a Southern California color form, possibly an undescribed subspecies, though its existence is well known. It is one of the largest of the Chalcidoids in the U.S., and the only one exhibiting wing-folding as part of its mimetic morphology (parasitic on Megachilid bees).
This is a female - note that ovipositor is curved dorsally over abdomen; see also adjacent photos, especially third from left.