As a Master Gardener who works in the plant clinic each month, I help clients diagnose various plant problems. Some folks bring in branches that have been attacked by what they think is some sort of disease. Their branches will look like the ones in the photo above (you can click on it for a closer view).
I'm always happy to reassure them that it's just lichen growing on branches and that it's quite harmless.
What we're looking at when we see lichen growing on a plant or a surface is a partnership between a fungus and either a type of algae or bacteria. They grow cooperatively to take advantage of the chlorophyll found in the algae or bacteria so they can conduct photosynthesis to survive. They grow especially well in the Inland Northwest since we have relatively dry conditions.
Lichen will not harm the plant they are growing on so when you see them, just enjoy their colors and unusual shapes and consider them an interesting part of the ecosystem around us!