It dawned on me that Melvin Turk's father's disappearance coincided with WW1 - so I check the WW1 draftee list found on Rootsweb.
Robert Roy Turk lived in Billings, Montana when he enlisted on 5 June 1917. He had one wife and one child. He was born 31 Aug 1890 in Red Lodge, Montana.
I would be interested in knowing who Robert Roy Turk's parents were. But it is clear now that Melvin was not my grandmother's nephew. That is disappointing! I know that she had two niece/nephews who were the children of her brother, Archie Heath Turk who d. ca 1922 in Wisconsin. Sure would like to find them!