hello,  I'm not certain what would be causing that.  It could be a number of things, But the tree looks generally healthy, and you may not need to worry too much.  I'm curious if it is a new disease we have been seeing called Douglas-fir phytophthora, or red needle cast.  However, that cannot be identified without laboratory testing.  Depending on your level of interest, it would be great to have the Plant Clinic here at OSU test these leaves for the disease.  However, it costs money.  Here is the website.  If could could clip a couples twigs with the brown foliage and send them to the clinic, I could pay for the costs.  https://bpp.oregonstate.edu/plant-clinic/about

Read, how to submit a sample before mailing the sample.  and inform them that David Shaw (OSU, Forestry) will pay for the sample processing fees and that we would like to know if Phytophthora pluvialis is present.

Thanks