I knew this from the beginning. It's quite obvious that the darkest part of this painting is obviously the vertical cliffs in the shadows. However there are three colors of the darks in this composition due to the distances from where I was standing. The further it goes, the lighter and bluer it becomes. I finally put it in place. They're still wet and reflect lamp light so not so clear in this photo, but they're there.
Now I really need to define the colors and values of front ground. Then I would call it done.