This female conopid was found visiting a very floriferous patch of wild buckwheat (Eriogonum nudum var. westonii) during the warmth of mid-day...along with a large number of other insects, many of which were Hymenoptera, and which she may have found suitable as hosts for her larvae.

It's clearly a female from the conspicuous "theca": an elongate, triangular-pyramidal shaped projection emanating below the abdomen on the 5th sternite. The theca is indicative of females in the subfamily Conopinae, and is said to be used to help grasp and pry open (somewhat like a "can-opener") the tergites of bees, where the female conopid inserts her eggs. The theca is often very large in Physoconops (less so in Physocephala).

She keyed unequivocally to Physoconops (Gyroconops) sylvosus in Camras & Hurd(1), Camras (1955), and Williston's 1882 key here (under the synonym Conops sylvosus). Overall, Williston's detailed description fits very well, although the "interrupted" anterior darkened band of the wing...emphasized in a number of keys and descriptions...is only vaguely discernible here (more so from some angles than others). That initially gave me some pause, until I read Bank's detailed description of his Conops arizonicus, which is a synonym of P. sylvosus, where he described the wing pattern as having:

    "...marks are like those of C. sylvosus, except that here the cloud extends unbroken to the fifth vein..."

So, although distinctive for P. sylvosus, the apically interrupted aspect of the anterior darkened pattern of the wings can apparently be subtle or even absent.