I believe this is a female Ocyptamus fascipennis --- based on the well-separated eyes, the good match with the fairly consistent shape and color patterns of the O. fascipennis images on BugGuide, and the geographical locale. It (along with numerous other insects) was feeding on flowers of the desert shrub Psorothamnus polydenius, in the Pea family (Fabaceae).

[I trust someone will correct me if I'm wrong here on the gender or species!]