This is Proctacanthella cacopiliga. It is in the Asilinae subfamily with Proctacanthus and the Efferia. Looks kind of like a rufus-colored miniature Proctacanthus with an unusual bulby genital appendage in this male. These were at Holla Bend and they were flying up and down the grassy pathways near an open cow grazing area. I have not found them elsewhere but they are known from several counties now. Fairly widespread eastern species. The other five members of the genus are all western and Texan. See image of exquisita for comparison from OK.

This is the female. Note how bright reddish black that terminus is. With a very white face. The transition colors in the terminus over the preceding segments is fairly distinctive once seen in this species. These seemed to strongly favor ground perching as opposed to some Proctacanthus.