Perhaps one of the leaf-cutting bees.

I checked, it s not a leaf cutter bee

Well, wild guesses are probably 10% correct. Does one thing in the image eliminate it from the leaf-cutters, or rather did it not match up with any images you viewed?

Appears too slender to be a leaf cutter bee.

I also see a few dark markings on the wings, but not clearly enough to make an ID. Nor can I decide if 1 or 2 pair of wings.

Sort of fly-ish. Wish I could see antennae.

I rotated and enlarged the image on my computer initially, there are two sets of wings, each wing having two dark dots. Head and legs very bee-like. I thought the insect was rather plump (and larger than local leaf-cutters).

I checked a number of resources before and after posting (web, local and regional field guides etc) and did not see this insect on any page. I have another photo with half a dozen on the same wild oat type of grasses. Allof them were seen early afternoon hanging on the plant. They were not aggressive at all. The photo was taken near where cattle sporadically graze I hope this info helps I can post the other photo soon. I may take the photo. To California Academy of Sciences to see if they can help. I will share what I learn. Stand by

Standing by.