Sonny was kind enough to tell me the story of his truck. In 1953 he went to the Wyoming Department of Transportation to get his license plate. No one wanted the number 666, but he did. And he's had it ever since! I suppose this is a part of Wyoming nonconformity.
Later, I returned to Sonny's place to say hello, and I found him working in his garage. While there, one of the many deer which inhabit Thermop came into his yard and sat in the shade next to his pickup.