Just because there isn't anything under mt.chilliad that doesn't mean there's nothing to unlock or find.
When we worked for 100% we HAD to talk to Omega (UFO guy), who talked about a crashed ufo, and little did we know, there actually was a crashed ufo, he was our first lead to this UFO mystery going on and when we reached 100% it unlocked these weird stuff. UFO at mount chilliad, UFO at Fort Zancudo, UFO above the UFO camp, and all 3 well hidden and well made, they are not just some still texture items.
Is a 100% reward really rewarding by giving us 3 hidden/secret UFO's that spawn during different time and weather settings, and not to mention the weird scientist with their FIB agents as guardians. They wanted us to see the mural at mt. chilliad, they wanted us to see the marking beneath the platform at the top, they wanted us to see "come back when your story is complete". There HAS to be something more than this!
And whatever "it" is, it does not have to be under/within the mountain, it can very well be a loading screen that takes us to another created place/location.
I do believe that there is something to unlock/find, we just need to continue searching, even tho we already have 10000+ theory's and tried out tons of different things, there has to something we are not seeing/doing right.
And please, if you are here to tell that there is nothing to unlock/find and that it's a waste of time, don't write, because it's not like we are going to give up because of your statement, just let us try to prove you wrong. Just leave the topic and let it be to us who actually are looking for easter eggs and trying to solve the mysteries.