At first, I thought it might be some kind of water treatment plant. But it's too small to be that from what I know about those systems. (Could be wrong.) Then I thought it might be someone's house. But I'm not sure and it's a mystery.
It appears to be connected to the Thousand Trails Pacific City RV park there, but it's not on the resort map linked on their site. If you really wanted to know I'd say calling that park would be your best follow up.
I thought it might be a helipad as well, but the proximity of the trees around it rules that out. Even if there was a skilled enough pilot with the right weather and air current conditions... It would be quite a challenging land. Let along take off. Why would there be a helipad there in the first place, was a following question I had, and couldn't determine.
It is twice the size of a small helicopter pad. It is on the high point in the area, and there's a large commercial for building just to the SW. I'm not disagreeing, but I'm at a loss othwrwise. Missle silo?