widespread in w. U.S. Often have individuals with reddish legs. Is a small, curved spine at apex of anterior tibia (not quite visible in photos).

I highly appreciate your expert knowledge.

I read that Cophura brevicornis is usually found in montane (Ponderosa) Pine forests.
That matches very well.

I've added another photo of the same individual showing the forelegs.
But I'm not sure it shows the curved tibial spine.

The photos are not well illuminated, as they were taken in the shadow of a pig pine tree on an overcast day.
The colors are also not as vivid as they could be.
I lightened the photos up a bit to show more detail in the dark areas.

This robber fly landed on the pine log shortly after a lifted some of the bark.
Could its favorite meal be hiding under the bark ?
Don't Robber flies predominantly predate in-flight ?

The curved tibial spine is very small in Cophura and you would probably have to catch one in order to see it. Yes, nearly all Asilidae only go after prey while it is in flight. Cophura brevicornis would forage after quite small, flying insect prey that it would detect while perching on a log or similar substrate. Other species of Cophura utilize a variety of perching sites: leaves, twig tips, grass stems, rocks, soil, etc.