high mountain
峨 centers on a towering, steep mountain. The single meaning "high mountain" captures a sense of imposing height and ruggedness.
峨 combines 山 (mountain) with 我, which likely contributes the sound. The character expresses the idea of a lofty, imposing mountain.
The left side is 山 (mountain), and the right side 我 looks like a proud, upright figure. Picture a mountain standing tall and majestic like a self-assured giant.
For ガ, imagine a high mountain so steep that climbers gasp "Ga!" when they see it. The gasp "Ga" cues ガ while the mountain towers above.