2D picture with relief: how to select deep ends?

[Xogroroth]

Thank you for responding.

So ...:
I was 2 versions behind, the path is correct.
I figured that the 2 versions older Gimp still had to do it?

I am used to not update working programs.
Had issues in the past where updates botched up, both in drivers as in programs.
Hence ... .  

Never fix what ain't broken.