Apologies for the somewhat poor photo quality here...but I'm very curious about this fly, as it had interesting behavior and was visiting an unusual plant. I'm guessing it's a tachnid, from the bristly abdomen and the conspicuous white calypters. (At least I think that's a calypter, between the wing base and abdomen).

When I first spotted this tiny fly from a distance, I mistook it for a bee for two reasons. First, because its methodical, quickly sequential flight pattern of visiting numerous tiny flowers of the native buckwheat Eriogonum ordii. And second, because the bright calypters looked like pollen collecting apparatus. (Perhaps it similarly fools others who might wish to molest it, though it's unclear to me whether predators would be deterred by so tiny a bee mimic.) I'm wondering if it was busy visiting the flowers to take nectar, or if perhaps it was laying eggs that could hatch into larva and later ambush visiting insect hosts...assuming it is a tachnid. Unfortunately, the latter hypothesis didn't occur to me until after I left the site, or else I could have examined some of the flowers with a hand lens for possible eggs.

As always, ID ideas or other interesting comments are welcome and appreciated.