Answer:
I think imagery is the most prominent in developing the tone.
Step-by-step explanation:
The author uses all sorts of imagery to describe what the setting looks like:
"The curly grass about us was on fire now."
"There was a shimmer of gold on the brown river."
"Out in the stream the sandbars gineredke glass and the light trembled in
the willow thickets as if idle flames were leaping among them."
All this helps to create a tone that shows the author sees the setting as beautiful. The setting seems very cherished and special because of how detailed and lovely it seems.