With considerable patience, attentiveness, and luck...I was delighted to find this male Rhaphiomidas nectaring on Eriastrum densifolium, and also the female below:

 

I observed in this area for a good chunk of the afternoon, and about six different times saw a single male or a single female...which, while in the field, I suspected were the same two individuals returning after fairly long intervals to nectar. But scrutinizing the photos I'm now thinking there were at least two different males among those I photographed...two more photos appear below:

   

I've gone through the keys in Van Dam(1)(2010) and Cazier(2)(1985) numerous times...as well as the relevant species descriptions and discussions in the latter reference...and as best I can determine, the male and female here go to Rhaphiomidas acton in their treatments.

Note the very bulky heart-shaped external lobes of the teminalia ("epandria" per Van Dam, or "hemitergites" per Cazier), which are much wider than the 5th tergite; and also the very long gonocoxites...the tips of which can be seen barely peaking out from below the ends of the hemitergites. These are characters of R. acton rather than other candidates (such as R. aitkeni or R. auratus...whose terminalia are more elongate and narrowly heart-shaped; and gonocoxites are shorter). And though the tergites here lack the black maculations more typical of R. acton, Cazier states that the species is the most variable in the genus, and "males vary from having the abdomen nearly immaculate to having black markings on all tergites". The femora are not completely visible in this image, but they are in my other male images from this locale (which I believe are the same species, if not the same individual), and their femora were orange (with the anterior femur somewhat darker...but not piceous as described for P. aitkeni, which also has narrower epandria).

The locality here is within the northern portion of the far-eastern CA range of R. acton where Cazier indicated intergrades of R. acton acton and R. acton maehleri commonly occur (see map and discussion on pg. 254 of (2)). The upper edge of the epandria of maehleri is noticeably undulate according to Van Dam(2010), but I got no good profile shots which would show that character. The other character Cazier stressed for distinguishing R. a. maehleri is that males and females were dichromatic (i.e. of distinct coloration of abdominal tergites and overall vestiture) and dimaculate (i.e. with different abdominal maculations patterns...or lack thereof). The female did seem paler, but both were virtually immaculate here. So I guess "intergrade" of R. a. acton and R. a. maehleri is my best shot at subspecies placement.