Do you have a copy of Mary's obituary? The Whitman County Genealogical Society will search for an obituary for a fee. Hopefully that will provide a listing of all her survivor's.
I found the 1930 Census and she had a granddau Mary J. Poage b. abt. 1920 in Whitman Co., WA. I tried to find her marriage info but didn't.
In 1939 Charles, Mary, Marguerite and Mary J., student were living at West 1217 Eighth Avenue, Spokane. Source: Spokane City/County Directory 1939.
Marguerite Poage Born: 19 June 1889 Possible Last Residence: Spokane, Spokane, WA Died: July 1976 Source: Social Security Death Index
There is a Spokane obituary volunteer at freepages.genealogy.rootsweb.ancestry.com/~obitl/volwa.html .Hopefully Mary will be mentioned in Marguerite's obituary (if one was published).
I did find a Mary Poage Married: 27 Marcy 1949, Wallowa Co., Oregon Spouse: Austin Bartin. Source: oregon marriage indexes 1906-2008.
You could post another query in Wallowa Co. about how to verify this marriage or contact the Wallowa County Clerk, www.co.wallowa.or.us/administration/clerk/index.html to order a copy of the marriage certificate.
However, I didn't finddeath info for Mary Barton. Successful Searching!