This is an uncommon, but routinely observed, phenomena sometimes called stimulation broom. No one knows what causes this, but some type of stimulation must be involved. Brooming is a general term for branches that become abnormally clustered, or lose apical dominance and sprout lots of branches from a local area.

Douglas-fir dwarf mistletoe does not occur west of the Cascade Mountain crest in central and northern Oregon, so likely not that.

The classic pocket guide: "Common Tree Diseases of British Columbia" by R.E. Foster and G.W. Wallis from 1974. (Canadian Forestry Service) has a picture of this exact brooming. The photo is titled, "large stimulation broom in the crown of Douglas-fir, cause unknown." 

That sums it up. These occur throughout the NW, but no one knows what causes it. 

A mystery! 

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