I'm relatively new to Houdini, however, I have pretty big experience in CG field and computer modeling in Physics. I wish I knew about Houdini when I was studying in university 12 years ago. Now I just can't stop playing with all that awesome tools.
I was inspired by video https://www.youtube.com/watch?v=Vx_kYEUvYCA&t=1s This video give you general idea how this kind of mountain can be done.
I made some extra changes. at first stage I created random base with points scattered so that I have more of them in the center. After creating basic shape of the mountain structure. I transfered it to VDB. Played with noise. After that I used cool tools for working with Height Fields to make the bottom part of the mountain. I added some nodes to create and process different masks based on debris, hight and some other attributes. I also added AttributeVOP node to create procedural texture. Scattering of the stones is based on debris and hight attributes. The final model has 50 Million polygons. Rendered with #Redshift. Preparation stage took about 3-4 minutes. With the option "Sequence Rendering Full Scene Reload" off, rendering of each frame was about 1 min 30 sec.
Some wip images and setup of the AttributeVOP node for textures can be on my Artstation page https://www.artstation.com/artwork/4b9lQ2