The narrator's tone is a distant calm and nostalgic one but with a foreboding overtone, and the imagery Steinbeck chooses is integral to creating the tone. So as not to confuse tone with mood, let's clarify that both tone (narrator's feelings about the subject) and mood (reader's response of feeling to the story) both employ vocabulary, also called diction. These diction choices include the vocabulary of imagery. The distinction is that while tone employs only vocabulary (diction), mood employs vocabulary (diction), setting and description. This means that tone and mood may both draw on imagery and in some cases may correspond, whereas in other cases they may differ so that the narrator may have a different feeling about the subject than the reader feels in responding to the story.
To start out, the feeling of distance in the tone is established in the epigraph in which the imagery of metaphoric rootedness is applied to mind and heart and in which the dichotomy of good-bad, black-white is established. Remembering that tone is established at the outset of a work, the epigraph and first paragraphs present visual, auditory and vocal imagery. The calm tone is most strongly set out in the auditory imagery of the roosters crowing, the pigs turning twigs and the birds "chittering and flurried."
The vocal imagery lends the feeling of nostalgia, as of a pleasant distant memory, through the mentions of music and songs. The morning waves make songs; Kino's people are "makers of songs;" everything heard, seen, thought, done became a song for his people. It is also in the imagery of song making that the element of foreboding enters the narrator's tone: The songs were made "very long ago" but are not made now. Only personal songs are made, but Kino can't speak of his, whereas, in the past, songs were shared among the whole people.
The other component of imagery that adds to the feeling (tone) of foreboding is the visual imagery at the very beginning of Chapter 1. The visualizations are of "near dark," stars that "still shone," the dawn a "pale wash of light in the lower sky to the east." These half shades of light and dark (antithetical to what the epigraph says of the story) produce foreboding because of the eeriness that accompanies nearly dark moments or nearly light moments in the world. This concludes the summary of how imagery in The Pearl creates the narrator's feelings, or tone, about the story being told.