The novel is loosely structured as a diary and can be described that way.
The following characteristics outline the novel's diary-oriented structure: The narrative is written in a first person narrative perspective. There are dated entries. There are reflections on Sam's life on the mountain that seem to be meant only for his own eyes later.
Despite the above mentioned characteristics, the novel does not entirely match a diary structure. The events recounted are all told in recollection or retrospect, for the most part. The narrator includes and comments on the actual diary entries, even commenting on the writing materials used during the writing process of the diary. Much of the story is not clearly intended for Sam's own eyes, but is written with an intention to communicate to another person or reader.
Ultimately, this novel is structured as a mixture of at least two forms of narrative, with one form being a diary and the other a retrospective narrative chronicle.
Some portions of the book are introspective and philosophical, while others contain notes of daily activities, diagrams, sketches, and even recipes.
With the drawing and recipes, we see yet another mode at work -the mode of a guidebook.