The poem in question is best described as a ballad, characterized by its narrative form, rhyme scheme, and rhythm which frame the subject of existential contemplation in a timeless manner.
The form that best describes the poem provided by the student is ballad. A haiku is a very short Japanese poem that follows a specific syllable count; free verse does not follow a regular pattern of rhyme or meter; and a sonnet has 14 lines, typically written in iambic pentameter.
This poem, however, describes a narrative, contains a rhyming scheme, and has a rhythm that is common in ballads. This song-like poem often tells a story and therefore meaning can be drawn from both the narrative and the lyrical form.
Given the poem's subject matter, which touches on contemplations of life and afterlife from the perspective of a cowboy, the ballad form reinforces the sense of a timeless and universal theme. It creates a mood that resonates with the storied history of cowboys and the open prairie, while addressing existential questions. Hence, the ballad structure enhances the poem's reflective and somber tone, which is centered on the journey between life and what comes after.