When I go north to Canada I drive through the Purcell Trench which is a vast valley going north and south in the Idaho Panhandle. It's pretty amazing and these pictures don't really do it justice. Today there was a forest fire burning just to the west and it was creating a lot of forest fire smoke that was filling the valley.
The picture above is looking north into British Columbia, and the picture below is looking south into Idaho. That is forest fire smoke in the lower picture, not clouds. I had to drive into that and I'm getting over a cold. You should have heard me coughing! To get the full effect you can click on the pictures to make them bigger, but they still don't do that valley justice.