Found nectaring on flowers of Asclepias subulata.

The rounded apex of the marginal cell...apically separated from the wing edge...indicates this is indeed Pepsis (e.g. rather than Hemipepsis or some other pepsine genus). And the relatively straight antennae indicate this is a male.

If this were a female, the very shallow angle made here between the marginal cell and the costa (see full-size image) would clearly put this in the "P. rubra-group", from the 1st couplet of the key on pg. 56 of Vardy(1)(Part 1.).

But this is a male, and I'm not sure whether that "shallow angle" character above extends to males as well. But even though most of the couplets in Vardy's key for males involve aspects of the subgenital plate (not visible in my photos)...if this is indeed in the "P. rubra-group", as I suspect, then by eliminating taxa that don't occur anywhere near California, as well as those whose males have dark apical bands (i.e. P. thisbe and P. chrysothemis), it seems this is P. pallidolimbata.

Another useful character, the mesopleural tubercle, is located (when present) midway along the ventro-lateral edge of the sclerite just above and in front of the middle coxa...see the labelled position "mt" in Fig. II here). A small "tooth-like" mesopleural tubercle is visible in the full-size version of the 2nd image of this post. That eliminates P. thisbe here but not P. chrysothemis. However, again, both those have a dark submarginal band apically...which is absent here.

Going through the key in Hurd(2)(1952), and without assuming were in the "P. rubra-group", by reading descriptions and again eliminating choices corresponding to taxa far out of range from Baja California and having dark apical bands, I again arrive at P. pallidolimbata here.