There may be many individuals flying over a lawn, but each female digs her own burrow six to ten inches deep and one-half inch wide. (They do not nest together.) The soil is dislodged by her mouth and loose particles are kicked back as a dog would dig. The excess soil thrown out of the burrow forms a U-shaped mound at the entrance, causing unsightly mounds of earth on the turf. This ground-burrowing wasp may be found in sandy soils to loose clay in bare or grass covered banks, berms, hills
as well as raised sidewalks, driveways and patio slabs. Some may nest in planters, window boxes, flower
beds, under shrubs, ground cover, etc. Nests usually are made in the full sun where vegetation is sparse
, especially in well-drained soils. Occasionally they establish in golf course sand traps. (A very gravelly or bare area is preferred.
And that is exactly where I photographed it - on the very sunny, dry, gravelly, and BARE hillside of the waterfall!