dense mountain vegetation
岶 centers on thick, lush plant growth covering a mountain: dense mountain vegetation.
岶 combines 山 (mountain) with 白, which likely contributes the sound ハク. The exact historical development is uncertain, but the structure suggests a phono-semantic compound where 山 gives the meaning and 白 the reading.
A mountain 山 covered in a blanket of white 白 mist so thick it looks like dense vegetation from afar.
For ハク, imagine a hiker hacking through the dense mountain vegetation: hack -> ハク, as you clear a path on the mountain.
—