how to create mountain contour lines

I can tell you how to create something vaguely similar in Illustrator, but not something based on an actual mountain. I can't see a way of doing that without either painstaking illustration or an actual 3D model.

If this is useful to you at all, use the following steps:

1. Using the grid tool, create a 100x100 grid.

2. Apply an envelope mesh (Object > Envelope Distort > Make with mesh). Give it as many rows/columns as you want, but larger numbers will make it hard to manage. This example has 10.

3. Rotate the whole thing 45 degrees. Object > Transform > reset bounding box, then flatten the whole thing somewhat (this gives you more interesting angles to work with).

4. Pull at the mesh points to adjust your mountain range.

Under Object > Envelope Distort > Envelope Options, you may want to set fidelity to 100, or you'll get parts where the paths pull away from the mesh in unwanted ways.

But as I said, you're unlikely to be able to fulfill your criteria this way.