Possibly Golden Digger wasps, Sphex ermineus and possibly a mating sequence. One of the wasps was initially sighted head first in a hole dug into gravel, trying to drag something out. The second and third images show a second wasp having been dragged from the hole and what appeared to be mating starting, as shown in closer detail in the first image. The first wasp tried to fly off with the second wasp but it escaped and flew away. One of the wasps eventually returned to the area as seen in the fourth and fifth images and circled around the holes in the gravel before flying away. This behaviour has been seen before with Bembix wasps so presumably it was an attempt at mating whilst the female wasp was digging a nest hole in the gravel.