Portland is right on the Columbia River delta that the Eastern Washington flood basalt flowed through to get to the ocean. If you go closer to to Mt Hood there should be some outcroppings here and there along the road. But if you want to see large batholiths then NE Oregon in the Elkhorn mountains or SW Oregon near Medford and Granite pass.

Again the reason we don't see as many large granite formations are because of the trees and soil covering them up. So you have to find where it as been eroded away or where there has been massive uplift.