those are incense cedars.... the Eugene area is at the northernmost region of these trees, so any issues with the species will show-up in these areas. Incense are sort of a finicky tree. You see lots of "flagging" (intermittent dead tips and branches) on these trees. It is a stress indicator. Cedar of all species have issues with soil disturbance.....but not sure what's going-on in your area. It looks worse than it is from a biological perspective. And there is pretty much nothing you can do other than a wait-and-see attitude. As far as watering, if you're going to water, do a heavy application (very slow running hose all night)> Don't do the shallow, daily watering. There can be instances where that does more damage than good(shallow watering only feeds the grass and shrubs.. So that's about all I know..............