Hello, it appears to be evidence of woodpecker foraging (possibly pileated woodpecker) on wood-boring beetles that are within the dead/dying trees. Typically this level of woodpecker drilling would be secondary to what is killing the trees and is not necessarily a direct cause of the tree's decline. The wood-boring beetles that the woodpeckers are feeding on are also generally secondary agents, in that they are feeding on the wood of dead/dying trees. It is possible that there is some sort of pest or disease that are killing the trees in the first place, in which the boring insects and subsequently woodpeckers are moving in after. More information may help us diagnose what is causing the decline (the extent and layout of other declining trees and pictures of foliage/wood). These dying trees can be very important for a variety of wildlife and woodpeckers create cavities in trees for other critters to use later on. If you'd like to determine what may be directly causing the tree decline, you can reach out to your local Extension Forester, Lauren Grand. 
https://extension.oregonstate.edu/people/lauren-grand