I am not entirely sure, but this bee fly may be dropping eggs into the burrows of Andrenid bees. It was flying around the same general area, stopping frequently to rub its abdomen in the soil before taking off, circling around, landing in the vicinity, then back to abdomen rubbing, or seeming abdomen rubbing. I could never get close enough to see well and these photos (this and the next one) are greatly cropped, taken from some distance.