The signs were there on the ground under the desert willow tree (frass pellets), and sure enough:
Looking back, I posted about a similar one on October 31 in 2012.
We were surprised to discover something else related just a few feet away.
The adult's wing color helps camouflage it as well. Even on this light colored wall, the light and dark pattern helped hide it in the mottled shade of the nearby leaves.
Have you ever discovered a rustic sphinx? Was it well camouflaged?