I live like 2 hours away from you so I don't know if this will help but, it looks like The Willamette River in that area is pretty close by and it has lots of sloughs that trail off it. I am sure they are congregating in and out of the sloughs that trail off it for I have seen them do it a week ago off a slough from the Columbia. The slough was only about 4 feet wide. Anyways, I have never caught a Carp off the Willamette if memory serves me right, but I do remember seeing them in a "flat" cove with a rocky bottom; specifically Clackamette Cove located at Clackamette Park which is around my area. That area has more of a "stagnant" type of water, rather than fast flowing.
Another thing that would help you is that, some of my specific fishing spots I cast at and still fish for Common Carp, are also PRIME Largemouth Bass spots. I know a guy that pulled a 6 lb largemouth out of the same hole I got the 25 lb Common Carp. So this might make you think twice before casting at a certain area.