Tree Tunnel. Crossett Western #10 sure looks as if she's charging out of a dark tunnel carved into the rock above the East Fork of the Lewis River, but in reality, it's just a tall stand of timber on the viewer's left, growing up beside the rocky cliff on the right. It's just a "tree tunnel", but from this perspective, it is pretty convincing. The Chelatchie Prairie Railroad does feature a real rock tunnel, and in fact, it is only a few hundred yards ahead of where the train is now.
Note the bright, green moss growing on the rocks above the locomotive. There is a lot of this moss in Washington and Oregon. The wet, marine climate of the Pacific Northwest is very conducive to the growth of this type of vegetation, and I've observed it not only on rocks, but on trees and even buildings. As you can see here, it's pretty hardy stuff that easily clings like glue to even vertical surfaces.
