I've started with the plaster work on the mountains.
I use a mix of WS moulds, home made latex moulds and alu foil.

The plaster is regular plaster of Paris.

I prefer to cast in situ. I wait until the plaster shows small wrinkles in the mould before placing it on the mountain.

I carve the surface with WS rock carving tools.
May need some more plaster in places.

I test painted the mountain...

I use regular acrylics and WS earth pigments.

First ochre.

Then burnt sienna.

And finally (?) gray stone pigment.
As it is supposed to look Colorado-ish, I hope this is the way to go.

It will lighten when dry.

Then some dry brushing.

I'm trying to match some photos I have of the Colorado mountains.

The color lightened a bit when it dried.

But the dry brushing went well.