I checked the Burnett County Cemetery listings and did not find George or Ethel Campbell on any of the lists.
I did find some family info in www.familysearch.org
that I am assuming is the same names. Place of birth for George is listed as Michian and place of birth for Ethel listed as Minnesota. In the 1930 census - Ethel is listed as a 40 year old widow. Children mentioned are Josephine M Campbell (5/17/1906) and George R Campbell - another area listed a Leonard