Upper trigram
☵
Water · Kan
Danger and depth.
FamilyMiddle son
ElementWater
Hexagram 39 of 64
☵☶ Obstruction
An obstacle that calls for a different route.
Lower trigram
☶
Mountain · Gen
Stillness and limit.
FamilyYoungest son
ElementEarth
The image
Water above, Mountain below.
Water over Mountain: danger and depth meeting stillness and limit.
That combination is the whole meaning of hexagram 39. Nothing about it is arbitrary — change either trigram and you get a different hexagram with a different reading, which is why the 64 form a system rather than a list.