I observed quite a few of these, mostly -as seen in these two photos- taking nectar in Cuscuta californica (California dodder), though a few feeding on Lepidospartum squamatum (Scale broom).

An added note: the key characters separating Eucerceris from Cerceris (see California Wasps of the Subfamily Philanthinae, by Bohart & Grissell. Bull. of the Calif. Insect Survey, vol.19; available as pdf: 1) are:

-outer veinlet of third submarginal cell meeting marginal cell well beyond its outer third; terga with median or submedian transverse depressions.....Eucerceris Cresson. This appears to be the case in this specimen. The tergal transverse depressions can also be seen in a Eucerceris I photographed last summer in the Colorado Rockies (that one was identified by Doug Yanega); see 2.

Revisiting the issue of gender: I count eleven flagellomeres; the seventh abdominal segment is barely visible. Thus, its a male.