At what point in My Side of the Mountain does the author create a sense of mystery, tension, or surprise and how?
There are a number of suspenseful episodes in the novel. Sam's effort to find and claim a baby falcon is quite tense.
In that moment, the description of the setting and action become highly detailed and specific, both emphasizing both the importance of the scene and creating a narrowed perspective that draws the reader into the experience. Here, the physical situation is dangerous with Sam precariously clinging to the side of a rock-face.
Another suspenseful scene occurs later, when Bando comes to the mountain. Here suspense is created through a controlled use of information as well as the use of a classic "red herring".
The "red herring" here is the police sirens going up and down the road near the mountain. Finding a man sleeping near his tree-house, Sam puts the clues together in a way that heightens suspense.
Sam has just heard police sirens from the valley below, so he deduces that the man must be on the run.
For a moment, Sam and the reader believe that the man is a criminal on the run. Through the use of the false clues and through the careful restriction of information, the author keeps the reader in suspense.