Fishing in the Mount Hood area can be tough in December because the lakes can be snowed in or frozen, however, Pine Hollow is a little east of Mt Hood and worth checking out.
In December on the Oregon Coast the ocean is usually too rough to fish and also December is our wettest month of the year so a lot of the time all the streams are high and muddy. But there are salmon and steelhead available. Focus on the smaller streams with fish hatcherys for steelhead such as North Fork Nehalem River and Cedar Creek. For salmon, the Wilson, Elk and Sixes rivers are the main rivers that have salmon in December.