The USFS recently published an aerial survey of forest disease and insect damage in the Bozeman area. The full map is here:
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd622553.pdf

Here’s an excerpt for Bridger Canyon:

Most of the damage is identified as WSB-DF/SAF-H = Western spruce budworm in Douglas Fir/Subalpine Fir with heavy defoliation. There’s also some DFB = douglas fir beetle, mainly around Green Mountain and Kelly Canyon.