Pioneers! O Pioneers!
There's one sound you'll hear over and over and over again in the poem, from the title right on through to the end: "Pioneers! O Pioneers!" That title, and the repeated refrain, set the tone of repetition that's put to use in other ways in the poem, too. Seriously, this speaker is pretty much the most repetitive guy ever, and the poetic devices he uses all revolve around repetition. Here are a few examples:
Anaphora. That's when a phrase gets repeated at the beginning of sentences or lines. He uses it so much in the poem, it's almost not worth going over examples, so we'll just point your attention to the very first stanza, which repeats, "Have you your?" twice. And the poem's just getting started.
Alliteration. Or repeated consonant sounds at the beginning of a word. Want an example? Okay, okay, we'll give you one. Check out stanza 11: "the mighty mother mistress."
Assonance. This term refers to repeated vowel sounds in a line. You won't see it as much as the other forms of repetition in this poem, but it does pop up on occasion, like in the line, "Lo! the brother orbs around! all the clustering suns and planets," (74). Hear those O's and UH's? That's assonance.
We also notice that in many places the sounds of the words mimic their meanings. We can hear the sharp sounds in "sharp-edged axes" (line 3). In the line, "From the peaks gigantic, from the great sierras and the high plateaus," we can hear the sharp distinction of those gigantic peaks and then the language levels out on those long vowel sounds at the end. And what's a plateau? A place where the land levels out. Fancy that. We bet if you took a close look at a few stanzas you could pick out a few of these sound-meaning correlations yourself.