I have uploaded a video on Backdrop Painting For Beginners - Colorado Mountains and Valleys to Youtube.

Segments include: 

Backdrop Preparation

Blending a smooth transition from horizon to overhead colors.

Basic clouds

Craggy Colorado mountains

Painting trees

Providing distance in your backdrop

Painting a distant valley

Here is the link:

https://youtu.be/Ae7SHHxh-KE