This fly appeared to be feeding on pollen from flowers of Baby Blue-Eyes (Nemophila menziesii var. menziesii). For scale, the anthers are supposed to be around 2-3mm long. So I'd estimate the fly is ~7-11mm.

I think this is a Syrphid...but I'm confused by it's wing venation. For instance:

1) Is the third longitudinal vein after the subcosta to be interpreted as R3 (with the next R4+5)? or
2) Is the third longitudinal vein after the subcosta to be interpreted as R4+5 (with the next M1 or M1+2)?

Another way to phrase my question:

3) There appears to be two longitudinal veins forming the edges of the (skinny!) 1st basal cell. They remain +/- parallel until meeting just short of the distal edge of the wing, and have two cross-veins. Is the anterior of these veins R5 or M1? (I thought it should be R5, but I'm not clear on the arcane art of wing vein structure/nomenclature!)

Anyway, due to my confusion, I couldn't figure out how many submarginal or posterior cells the wings had, and was unable to successfully key this individual using Cole(1).