See guide page for identification references. This small, attractively-patterned Bombylius was hovering and dipping its abdomen (ovipositing) over bare patches of soil along a trail. It was often over burrows of other insects, as shown here. In one case I saw a small hymenopteran emerge from such a burrow.

The flies would bask in the sun between bouts of ovipositing. There may have been males present as well--there were three or more flies in the same small area, and I'm not sure if all were ovipositing. (I did not see any mating activity, however.)

Others at this location, showing basking: