I was wondering what this moth is – basking in the heat
Living in Southern California in 100 degree+ heat brings out the oddest creatures. This moth is was baskiing in the sun atop our patio cover but has now flown. As you can see it is a significant size. It is over 2" from head to toe and has 5" wingspan when resting. It is the size of a small sparrow.
Both your moth and the Modest Sphinx are referred to commonly as the Big Poplar Sphinx. Some authors consider your moth, the western species, to be a subspecies of the other. Other authors consider them to be separate species. Here is as site that names your moth Pachysphinx occidentalis.