Have you seen him in the 1870 census. He appears to be in Portland, with his wife Kate. Living with them are a Nicholas Witman age 46, born Prussia, Alex Witman (born France, age 19) and a very old woman, name appears to be Martalin born France, age 105. In 1880 there is an Alexander Witman, born Ohio, age 29 living in Humboldt County California, with a son Nicholas.
These names seem to fit with the middle names of two of John's sons.