Complex sentence: About half of the portion of the district that had been in Benton County, Oregon was moved into the 4th district and portions of west-central Clackamas County were moved into the 3rd district.
Split into simpler sentences: About half of the portion of the district that had been in Benton County, Oregon was moved into the Oregon 4th District. Also portions of west-central Clackamas County were moved into the Oregon 3rd District.