I have been working on the ancestry of a friend of mine who is related to the Carl Fodness you mentioned (husband of Lydia Karch/Hartman). Do you know anything more about her family? Can't help you with the Karch ancestry, but in the 1910 census, Carl and Lydia Fodness were living in Grand Forks County, ND, and Lydia (age 24) said she was born in Illinois, her father in New York, and her mother in Louisiana. They had been married 4 years and had 2 children.
Interesting about the name change, though. Carl Fodness wasn't born Fodness -- he was the son of Nels and Mary (Fodness) Anderson. A brother of Mary (Fodness) Anderson's (I think his name was John Fodness, but I'm not sure) and his wife had no children, so they adopted Carl and he went to live with them in Grand Forks County, ND, taking on the Fodness surname. He was born in Lyon County, Minnesota, where his parents and brothers and sister lived.
Not sure if I have any information that might be helpful to you, but let me know if you have any questions.