I am not 100% complete, but working on it. In the meantime, I have a question or two and possibly, this is something you need to ask yourselves as well.
The Chilead ufo appears to be a hologram. Is the hippie camp ufo a hologram as well? The Fort Z ufo appears to be REAL. Here are the questions:
1. Why is ONE ufo real and not the others?
2. Why does the MC ufo only appear at 3am and storming? Where are the hints that point to this occurance?
3. The symbol at the top is a circle with a line through it. Some have suggested that this may be the "all-seeing eye". Not sure how they came up with that since the symbol under the deck is ACTUALLY an "eye". Therefore, it would lead one to believe that the top symbol is a spaceship.
4. Are all of the X boxes on the mural complete X's? Some appear to be just a slash instead of an X.
As to the poster who stated that there is a door in the tunnel under the mountain, there are actually TWO doors under there. One is labeled T 01 and the other is T 02. T 01 is on the north side and T 02 is on the south side. Both have a red light next to the door. However, at T 01, if you go up the stairs and back down again, the red light will go off. Move toward the door again and it comes back on. This does not happen at T02. The panel is definitely electrified because it sparks when shot. Could be a texture glitch but needs more confirmed reports.
My way of thinking, the mural represents the UFO as the easter egg to the jetpack. Since map overlays aren't panning out, it would lead one to believe that the mural is an underground map instead of an overlay. Then again, like any artifacts, relics or whatnot that are found on Earth can lead one to believe one thing by one particular individual and something totally different by another individual. Hence, the mural MAY only mean what you, as an individual, WANT it to mean and that there IS NO Garden of Eden...