Unidentified Lichen

As best I can tell, this is a species of Lobaria, although I am not sure which one. L. pulmonaria seems most likely, although it is described as having a mottled white and brown undersurface whereas the undersurface of this lichen seemed basically white. I noticed lichen such as this growing on a number of different spruce trees, but I have not observed it growing on hemlock trees so far.

Location: Indian River Valley, near Sitka, Alaska