This female was foraging on flowers of the sprawling perennial Phacelia ramosissima var. latifolia, along with at least one on-and-off pursuing male which I wasn't able to photograph. The phacelia patch was growing in a rock pile at a high point along a ridge where it was warm, sunny, and calm. The surrounding habitat was open (mainly non-native) grassland with nearby open oak woodland.

The wasp keyed to Pseudomasaris coquilletti in the 1963 treatment by Richards (see info page). The most salient character is the "yellow of upper orbits produced toward ocelli" for females of P. coquilletti...which is clearly visible in the image above. The (relatively) small size of the antennal knobs indicates this is a female (as well as behavior...she was assiduously collecting pollen all the time, while the male mainly patrolled the phacelia patch for females, and occasionally rested on the rocks).