In The Croods the girl Eep meets Guy who is travelling to the mountain, because the world is ending.
Here is a scene from the film that shows Guy telling Eep the world is ending.
How does Guy know that the world is ending?
It is based on Guy's theory that the earthquakes are a symptom of The End (of the world) and that heading to higher ground is the best way to possibly escape from the calamity. He's something of a cave-scientist and this is the kind of thing that cave-scientists do. It also contrasts his out-of-the-box thinking against that of stick-in-the-mud Grug.