State and Federal taxation records are available on microfilms through Family History Centers. There are county records, go to the counties in question.
Oregon Internal Revenue Assessment lists 1867-1873
United States, Bureau of Internal Revenue, microfilmed by the Genealogical Society of Utah, 1989 at the National Archives Records Administration - Seattle, Washington Branch. Some years missing.
Assessment lists 1867-1870 - film #1639854 item 3-10
Assessment lists 1871-1873 - film #1639855 item 1-4