Primary Sources: 1970 Census
The 1970 census was taken principally by means of a seperate questionnaire (a 9 1/2"x10 7/8" booklet) for each household, completed by the resident.
All answers were designed for self-identification on the part of the respondent, but the enumerator was allowed to fill in blanks by observation when this was possible. For item 4 (color or race), it was assumed that the respondent's relatives living in the unit were also of the same race unless the census taker learned otherwise. The enumerator's manual included a long list of possible written-in entries and how they were to be classified: For example, "Chicano", "LaRaza", "Mexican American", "Moslem", or "Brown" were to be changed to White, while "Brown (Negro)" would be condidered as Negro or Black for census purposes.
U.S. Census Bureau