cliff, bluff, precipice
崔 centers on a steep, towering landform: a cliff, bluff, or precipice. The core idea is a high, sheer rock face.
崔 combines 山 (mountain) with 隹, which likely contributes the sound. The character is used for high, steep places, but the exact historical role of 隹 is uncertain.
A mountain 山 with a bird-like shape 隹 below it: imagine a cliff so high that only birds can reach its top.
For ガイ, picture a guy standing at the edge of a cliff, looking down: guy -> ガイ, and the cliff is right there.