Not knowing what information you already have (may not have much as they didn't come to Washington until 1905) I only provided basics. Additional information can be obtained through obituaries, etc.
The 1910 Census for Dayton, Columbia Co, WA, enumerated 15 April.
Harry E. Mason, age 38(1871/1872), born in England, immigrated 1901/Naturalized, clergyman, married 14 years (1895/1896). Owned home on Washington Ave.
Elizabeth, age 34, born in Canada to both parents born in Canada, immigrated 1901
Arthur, age 9, born in Canada
Eleanor, 7, Washington
Beatrice, 5, WA
Harry 3 (twins)
The 1920 Census for Dayton, Columbia Co, WA, enumerated 8 January.
Harry E. Mason, age 47, born in England, immigrated 1900/naturalized 1918, bookkeeper/drug store, owned on Washington Aveue/Free(mortgage paid).
Elizabeth J, age 48, born in Canada, immigrated 1900, to father born in Scotland, mother in Canada.
Arthur, 19, born in Canada
Eleanor H, 17, WA
Beatrice 17(wrong age?), WA
Harry R, 12, WA
Margaret, 12, WA
Victor M, 7, born in WA
The 1930 Census for Dayton, Columbia Co, WA, enumerated April 8.
Elizabeth Mason, age 53, born in Canada, immigrated 1905, to both parents born in Scotland, immigrated 1905, owned at 212 Washington Avenue. Widow
Harry R, son, age 23, born in WA
Victor M, age 16, WA
The Washington Death Certificate Index:
Elizabeth Jane Mason, died 21 May 1940 in Dayton. She was 66 years, 8 months (about Sep 1874), her parents were Alexander Frame and Elischa Cambell (sic). Spouse was Hary(sic) E. Mason.
--There is no Harry Mason matching age criteria; however:
Harry Edgar Mason, died 17 Jan 1930 in Dayton, Columbia Co, father Edwin Mason, mother Mary Ann Cooper, age 88 (1842), married to Mrs. Harry Edgar mason.
Harry is buried in the Dayton City Cemetery, Blk G, Lot 39, Section 6:http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=ma...
Elizabeth, Blk G, Lot 39, Section 5.
Washington Birth Index 1907-1919:
Margaret Prestine Mason, born Jan 1907 to Harry E. Mason, Elizabeth Jane Frame
Victor Mason, born 12 June 1912 to Harry E. Mason ad Elizabeth Frame
World War II Enlistments:
Victor M. Mason, born 1912 in Columbia Co, WA, enlisted 7 July 1942 in Portland, OR.
Social Security Death Index:
Victor Mason, born 12 June 1912, died Dec 1981 in Portland, OR.
An online family tree owned by Susieakc:http://trees.ancestry.com/tree/13262909/person/-93262110?ssr...
identifies Victor M, was married to Nina Kelley, born 18 Aug 1921 in Bonham, Texas, died 2 Dec 1981 in Multnomah Co, Oregon. Oregon Death Index shows he died 15 Dec.
Victor is buried in the Willamette National Cemetery, 11800 SE Mt. Scott Blvd, Portland, OR 97266, Section L, Site 4949.
The 1930 Census for West Salem, Polk County, Oregon
Arthur L. Mason, age 30, born in Canada, imm 1905, to father born in England, mother in Canada. Advertising/Advertising Co.
Donna C, 30, born in S. Dakota
Nancy C, 2
Margurette, sister, age 24, typist/Real Estate Officer
The Social Security Death Index:
Arthur Mason, born 17 Jul 1900, died Dec 1985 in Portland.