"Department of the Interior, Heritage Conservation and Recreation Service: National Register of Historic Places; Annual Listing of Historic Properties", 44 FR 7416 (February 6, 1979), at p. 7569.
Oregon Parks and Recreation Department, Oregon Historic Sites Database, retrieved August 6, 2015. Note that a simple count of National Register records in this database returns a slightly higher total than actual listings, due to duplicate records. A close reading of detailed query results is necessary to arrive at the precise count.