Hi Lorrie and John,

My initial thoughts go to Douglas-fir Tussock Moths. Injury from these insects will often begin at the tops of trees where they will feed on newer needles and slowly the insects will work towards feeding on older needles. More information about the Tussock Moths can be found at this following link: https://extension.colostate.edu/docs/pubs/insect/05542.pdf

If you have spruce dying from similar dieback and with wilting terminals at the top of the trees, then I might think white pine weevil would be worth investigating. These insects can attack Fir but it is far less common: https://extension.colostate.edu/docs/pubs/insect/05606.pdf

These are very tall trees but if you can get a sample, perhaps from a smaller tree, the plant clinic in Jefferson county would be able to provide more detailed diagnostics. More information about the plant clinic can be found at this website: https://jeffco.extension.colostate.edu/horticulture/clinic/