What are some objects like mountains (irregular symmetric on both sides)?

Irregular symmetry = asymmetry?

asymmetric objects:

Faces.
Waves.
Trees.

Feet.

Trees.

Snowdrifts.

Breasts.

I mean I want to actually find volume or area of irregular shapes that have symmetry on both sides

A tree? An automobile? A person?

The last one has the advantage that you can calculate it and check your answer by using the person’s mass.

Things in the real world are messy, including mountains. Are you using slanted lines to represent mountains? That would be a gross simplification. You could represent ocean waves the same way, or maybe a coastline.