As you've probably guessed by now, that man was the father of the famous western novelist A.B. Guthrie, Jr. In 1947, the younger Guthrie had just finished his first book, and was struggling to come up with a title ... he showed a number of family documents to his editor, who discovered the quote above and knew he had a winner.
It wasn't long after The Big Sky was published that Montana's tourism people figured that they had a winner there, too ... and the phrase has been strongly associated with the state for over half a century now. I've always liked the slogan, though I confess I like it a little less now that the name has been appropriated by a destination resort catering to wealthy out-of-staters.
But so it goes. Here's a paragraph from the original novel, an evocative description of the sense of place that many of us feel about Montana.
Boone lay on his back and looked at a night sky shot with stars. They were sharp and bright as fresh-struck flames, like campfires that a traveler might sight on a far shore. Starlight was nearly as good as moonlight here on the upper river where blue days faded off into nights deeper than a man could believe. By day Boone could get himself on a hill and see forever, until the sky came down and shut off his eye. There was the sky above, blue as paint, and the brown earth rolling underneath, and himself between them with a free, wild feeling in his chest, as if they were the ceiling and floor of a home that was all his own.