In any given area or shape there are seldom more than three layers in George Post's paintings. Notice how he uses an invented pattern to describe texture, like the herring-bone marks in the conifers.
In this scene from Iceland (painted by me, on a good day), there are areas similar to George Post's shape followed by texture approach, and others that involve first reserving a white shape, as Rex Brandt did so well.
The homework is to copy a watercolor that engages you - one of these or anything you like. As you finish each layer, say, light, middle value and dark, take a moment to assess the effectiveness of the illusion of space, light and substance. You may be able to discover when in the sequence the illusions are established.