I'd search for a marriage in Navarro and/or Uvalde Counties. One possibility, John Champion Mason (6 Feb 1883 - 31 Aug 1957)? There is a death record for Harry Martin Mason (27 Feb 1914 - 21 Nov 1941) in Navarro with Cora Martin listed as mother. John C. Martin's WWI draft registration listed a blood-relative as next-of-kin. His 1920 census (look for surname "Masin") enumerated as widowed.