I've been looking over your Calvin problem today and I have a few comments to make. First, in the 1930 census, it looks to me like the place of birth for the two children, Sam and Anna Calvin, is shown as "Cherokee/mixed" and the race of the children is shown as "Ind." So it would be their father who was of mixed race.
In the 1920 census of Yakima Co., WA, John, Grace [wife], M. Carry [dau] age 7 b. OR and Sammie [son] age 5 b. OR, are all shown as "white" but I believe census takers often made a judgment about race based on the skin coloring of persons. Since Grace was John's wife in 1920, and in 1930, the remarried Grace [to Harold Walters] lists Sam and Anna C. as Harold's stepson and stepdaughter, that must mean that it wasn't Grace who was of mixed ancestry and if she's the mother of both Sam and Anna, then John didn't have a previous wife of mixed ancestry. Also in 1930, Grace had a son by her 2nd husband, Harold J. Walters, aged 1 yr. and some months and he's not shown as Indian so it can't be Grace whose of mixed ancestry.
You seemed to indicate you found John Calvin in the 1930 census. Or am I mistaken! I certainly couldn't find him in any census except the 1920 and that wasn't for lack of trying!