Three-fold Reference to Mountains:

1. … “;And every mountain and island were moved out of their places. And (men) hid themselves in the dens and in the rocks of mountains; and said to the mountains and rocks, Fall on us, and hide us from the face of him that sitteth on the throne, and from the wrath of the Lamb;” (Rev. 6:14-16). (Emphasis added).
2. … “And every island fled away, and the mountains were not found.” (Rev. 16:20). (Emphasis added).
3. … “The seven heads are seven mountains, on which the woman (Babylon) sitteth.” (Rev. 17:90). (Emphasis added).

Commentary: First two references deal with earthquakes, the third reference describes Babylon being nestled within seven (7) mountains. The Bible is very explicit that Babylon sits on Seven (7) mountains. There are no hills mentioned anywhere in Revelation. I take the Bible to be literal in this regard. You can research this and decide for yourself. There is futher proof elsewhere in Revelation, that suggests the interpretation of connecting these verses together to earthquakes is correct. Rev. 18-19 indicates, “; and there was a great earthquake, such as was not since men were upon the earth, so mighty an earthquake, and so great. And the great city was divided into three parts, and the cities of nations fell: and great Babylon came in remembrance before God, to give unto her the cup of the wine of the firceness of his wrath.” There are three more hints or indications that the earthquake that hits Babylon happens very fast; Verses: 18:10, 18:17 and 18:19 all indicate that Babylon is completely destroyed and annihilated by this great earthquake within just  “one hour”! There is a double of a double (2+2=4) in the three verses. Islands were moved out of their places / fled away, Mountains were moved out of their places / were not found. Foursquareness (4) represents an added measure of equal weight or importance.

Men think that mountains can protect them from the wrath of the Lamb, but that is not the case. The are so absolutely terrified by the wrath of Jesus Christ, that they would rather die on the spot by an avalanche, rather than have to face the Lamb, Jesus Christ. At the sight of Christ, they immediately know, or are convicted of their life of sin which will come with judgement. They would rather die now from rocks, and be hidden and covered up, hoping to escape the punishment that Christ brings on The Day of the Lord, than in having to face him at judgement. In their twisted fear and self-condemnation, they feel that being confronted by Christ directly, is worse than death itself. These poor men are truly deceived, they ignored the messages of salvation, grace and the forgiveness of sins through Jesus Christ. They had a chance to be saved earlier, and either ignored the message, didn’t believe it was true, forgot about it or didn’t think it applied to them, or procrastinated in thinking about it. In any case, it is now too late and they are absolutely terrified of the wrath that Jesus Christ brings. Pity, they now think their only escape is a pile of rocks. They literally feel like they could ‘just crawl under a rock and die,’ due to their shame and embarrassement at having rejected Jesus Christ. Painful, very painful. An understatement.