However, I wish it were that easy. Argia just doesn't seem to fit. Spacing & length of tibial & femoral spurs seem comparable to I. cervula , the sp. I had considered. Also, it has the 'orange' spots on back of head & betw. the eyes, dark line on top of thorax, narrow line (not pinched as in all Argia spp. in SLO County) on side. The pterostigma is light, as can be seen in many females, black dorsal stripe... It lacks the blue on top of segment 8, and is tan instead. Compare with a photo on Kathy Biggs' website ( I.cervula). Aside from the differences, this is the closest I've found so far. The female's prothorax has a central lobe along the rear margin, flanked by a pair of incurved pointed tufts of hair (Manolis, p.81(1)), one of which (or at least part of it) seems to be weakly visible in this photo.
I'd be happy to be convinced that this is something else (it is whatever it is), or perhaps these photos are not sufficient for ID. At the time I was more concerned with looking for a bombyliid fly (Conophorus collini ), which I did find.