Ninety-Two In The Shade by Thomas McGuane
The third novel by Thomas McGuane, this copy is from Lambeth Public Library in London. This episode also mentions Panama and Tom's movie, The Missouri Breaks. You can read more about the national monument in Missouri here: https://missouribreaks.org/the-breaks-story-map/
Tom even made the Paris Review! https://www.theparisreview.org/interviews/2867/the-art-of-fiction-no-89-thomas-mcguane