Since then, I've discovered that this insect isn't uncommon at all. In fact in some places it can be a pest of fruit trees. It is a Western species occuring from Colorado to the West Coast. In the North it occurs in southern Canada and ranges south into northern Mexico.
These pictures are of an individual that landed just outside my office west of Fresno this week. I'm not sure where it came from - maybe somebody's apple orchard. Finding it was like finding an old friend.