Mount Gordo is a small mountain in the north eastern part of the game island. A few points of interest are there, including the only yoga mat in the game other than the one at Michael's house, a building with an un-enterable interior, and some easter eggs.
Possible Relation to the Mystery[]
It's been speculated that the mountain glyph really refers to Mount Gordo because of the zig-zagging path on the glyph, and the fact that Mount Gordo has a zig-zagging on its side. Mount Gordo also has a building at the top which could be what the little square at the top of the mountain in the glyph is referring to.
Others have speculated that the concrete art at the hippy camp in Sandy Shores is referencing parts of Mount Gordo.
Ghost[]
GTA V - Mount Gordo Ghost Easter Egg HD Xbox360 PS3
There is an unrelated easter egg that appears at night between 11:00 PM and midnight on the side of Mount Gordo. A female ghost appears wearing a white dress and can only be seen if the player is standing far enough away.