Hi,
I found the Clarkson Family Tree, trees.ancestry.com/tree/10640549/person/6071637348 which contains your Gustave Helmar Holmberg and part of his family. Many of the larger public libraries provide access to Ancestry at no charge.

If you want to pursue his time in Whitman County, Washington, contact the Whitman County Genealogical Society, rootsweb.ancestry.com/~wawcgs/...

In 1930 Gustaf was living in Superior, Douglas, Wisconsin.
Gustaf H. Holmberg, b. MI, 39, accountant.
Ida C., wife, b. Sweden, 33, immigrated 1901.
Mary Louise, b. MN, 3.

Gustaf and his wife also had another child. Successful Searching!