ranges of hills stretching on beyond another irregular peaks
峋 centers on a landscape of irregular, jagged peaks stretching one beyond another in a continuous range.
峋 combines 山 (mountain) with 旬, which likely contributes the sound. The character is used to describe irregular, layered mountain ranges.
The mountain 山 on the left and 旬 on the right suggest a range of peaks that repeat like a ten-day cycle, stretching on irregularly.
For シュン, imagine the sound of wind rushing through the irregular peaks: shoon -> シュン, echoing across the mountain range.
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